Computing and Software Wiki - User contributions [en]

Asymmetric Digital Subscriber Line

2008-04-14T02:15:04Z

Johnstfd:

ADSL (Asymmetric Digital Subscriber Line) is one of the leading technologies for providing high-speed Internet service to subscribers. ADSL is a variant of DSL, and there exists a common misconception that the A stands for Asynchronous. This is incorrect, as ADSL is a synchronous service. It is, however, asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
===History===
Historically, Internet was served to people's homes through the use of voiceband data modems connect to the existing copper telephone line network. This network consists of twisted pair copper wires which run from a subscriber's home back to the telephone company's central office. The voiceband data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in harmony with a voice signal.

Traditionally, when ADSL was run to a home, a whole home splitter was installed at the demarcation point, the point where the phone line enters the home from the street. The splitter would filter all existing phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and install the device. Most ISPs have now adopted a much more passive stance wherein they ship the subscriber a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degradation of service for the consumer if they have more than 5 voiceband devices in their home. The reason for this is that the branching of the various phone lines causes reflections which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

===The Technology===
ADSL differs from standard DSL in that the data flow is asymmetric; data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are placed to Internet servers for websites or files, which are then downloaded to the subscriber's PC. Requests are much smaller than the files and websites they lead to, so there is little need for large upstream transmission capability. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, only recently has its bandwidth been fully used. The advent of technologies such as BitTorrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

 
==Functionality==
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
===Physical Setup===
The physical setup of the ADSL system is fairly symmetrical. The core of the setup is the DSLAM (Digital Subscriber Link Access Multiplexer), a device which is responsible for intermixing the voice and data signals on the downstream side of the connection, and for separating out the voice from the data signal on the upstream side.
On the upstream side, once the voice signal has been removed from the line, it is passed on to the phone company's telephony network. The data signal is passed onto the ISP's Internet backbone.
On the downstream side, the DSLAM combines the voice and data signals coming from the phone network and the Internet, and transmits them down the twister pair copper line to the subscriber's home. There is a physical distance restriction imposed here, of about 5km. This is the maximum distance that a signal from a DSLAM can travel without degradation. Beyond this point, Internet service may be intermittent, or slow, or just not possible. For this reason, ISPs will not provide ADSL to people living outside of the 5km service area of a DSLAM.
After the signal arrives at the subscriber's home, one of two situations is possible. Either a whole home splitter is installed, which filters the ADSL signal from the home's phone lines, and passes it along an unfiltered line to an ADSL modem, or the subscriber has installed microfilters on their voiceband devices, filtering out the ADSL at the wall jacks. Either way, the signal must now pass into an ADSL high speed modem, which will interpret the signal, and communicate with either a computer, or a router, providing Internet access. ADSL modems are power hungry devices and require their own power source; there is no way to incorporate them into a home computer system the way that voiceband modems have been.

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. The frequencies within the copper line are broken down as follows:
* 0kHz - 4kHz: Voiceband Services
* 4kHz - 28.875kHz: Unused buffer area
* 28.875kHz - 138kHz: Used for upstream transmission,
* 138kHz - 1104kHz: Used for downstream transmission.

Note that the upstream frequency range is much smaller than the downstream frequency range. This is the asymmetric nature of ADSL; in true DSL, the upstream and downstream frequency spreads are equal. Also note that ADSL is a full duplex technology, which means that signals can be travelling in opposite directions at the same time, on a single wire. An easy way to conceptualize the use of the frequency ranges is to imagine the ranges as "pipes" through which the various signals travel like water. The larger the pipe, the more water can travel through it.

The two main frequency ranges are further subdivided into smaller units, called channels, each of which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the channels on the line to establish which ones have the best signal-to-noise ration, a measure of how much interference exists in that channel versus how strong the ADSL signal is. Interference on a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antennae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of available bandwidth decreases with each unusable channel.

==The Future of ADSL==

===The Growth of ADSL===
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of Highspeed Internet. Due to the ease of installation, and the fact that it utilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fibber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away, and a new one is installed less than 1km distant).

===New Devices===
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
Up until recently, when someone subscribed for ADSL service, they would receive an ADSL modem from the ISP. This modem would then be attached to the phone line and the subscriber's computer, providing Internet service. If the subscriber wished to use more than one computer with the service, he would be forced to purchase a router. Lately, ISPs have begun to distribute devices where are being termed "Home Gateways". These devices incorporate the ADSL modem, a 4 port home router, and a wireless access point into one compact form factor. With home networking on the rise, these devices are expected to be extremely popular with home users as they will limit the clutter required for a home network, and centralize control of all aspects of the network into one device.

===Competition===
Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the successor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widespread adoption in Japan and South Korea where it is the predominant high speed Internet technology.

==See Also==
[[Wireless Network Security]] 
[[WiMAX]] 
[[Mesh Networking]] 
[[Designing a Small Business Intranet]] 
[[Internet Cookies and Confidentiality]] 

==References==
# ADSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/Adsl http://en.wikipedia.org/wiki/Adsl]
# Tyson, Jeff. ''How VDSL Works''. How Stuff Works.com. Retrieved April 7, 2008 from [http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
# Volf, Zahy. Anita Demayo. Roei Limoni. ''ADSL''. RAD University. Retrieved April 7, 2008 from [http://www2.rad.com/networks/2005/adsl/main.htm http://www2.rad.com/networks/2005/adsl/main.htm]
# Hamill, Hugh et all. ''Asymmetric Digital Subscriber Line''. Retrieved April 7, 2008 from [http://www.esatclear.ie/~aodhoh/adsl/report.html http://www.esatclear.ie/~aodhoh/adsl/report.html]
# VDSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

==External Links==
* [http://http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
* [http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]
* [http://www.speedtest.net/ Internet Speed Test]
 
----

--[[User:Johnstfd|Durandal]] 22:15, 13 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T02:14:50Z

Johnstfd:

Asymmetric Digital Subscriber Line

2008-04-14T02:14:10Z

Johnstfd:

ADSL (Asymmetric Digital Subscriber Line) is one of the leading technologies for providing high-speed Internet service to subscribers. ADSL is a variant of DSL, and there exists a common misconception that the A stands for Asynchronous. This is incorrect, as ADSL is a synchronous service. It is, however, asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
===History===
Historically, Internet was served to people's homes through the use of voiceband data modems connect to the existing copper telephone line network. This network consists of twisted pair copper wires which run from a subscriber's home back to the telephone company's central office. The voiceband data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in harmony with a voice signal.

Traditionally, when ADSL was run to a home, a whole home splitter was installed at the demarcation point, the point where the phone line enters the home from the street. The splitter would filter all existing phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and install the device. Most ISPs have now adopted a much more passive stance wherein they ship the subscriber a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degradation of service for the consumer if they have more than 5 voiceband devices in their home. The reason for this is that the branching of the various phone lines causes reflections which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

===The Technology===
ADSL differs from standard DSL in that the data flow is asymmetric; data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are placed to Internet servers for websites or files, which are then downloaded to the subscriber's PC. Requests are much smaller than the files and websites they lead to, so there is little need for large upstream transmission capability. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, only recently has its bandwidth been fully used. The advent of technologies such as BitTorrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

 
==Functionality==
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
===Physical Setup===
The physical setup of the ADSL system is fairly symmetrical. The core of the setup is the DSLAM (Digital Subscriber Link Access Multiplexer), a device which is responsible for intermixing the voice and data signals on the downstream side of the connection, and for separating out the voice from the data signal on the upstream side.
On the upstream side, once the voice signal has been removed from the line, it is passed on to the phone company's telephony network. The data signal is passed onto the ISP's Internet backbone.
On the downstream side, the DSLAM combines the voice and data signals coming from the phone network and the Internet, and transmits them down the twister pair copper line to the subscriber's home. There is a physical distance restriction imposed here, of about 5km. This is the maximum distance that a signal from a DSLAM can travel without degradation. Beyond this point, Internet service may be intermittent, or slow, or just not possible. For this reason, ISPs will not provide ADSL to people living outside of the 5km service area of a DSLAM.
After the signal arrives at the subscriber's home, one of two situations is possible. Either a whole home splitter is installed, which filters the ADSL signal from the home's phone lines, and passes it along an unfiltered line to an ADSL modem, or the subscriber has installed microfilters on their voiceband devices, filtering out the ADSL at the wall jacks. Either way, the signal must now pass into an ADSL high speed modem, which will interpret the signal, and communicate with either a computer, or a router, providing Internet access. ADSL modems are power hungry devices and require their own power source; there is no way to incorporate them into a home computer system the way that voiceband modems have been.

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. The frequencies within the copper line are broken down as follows:
* 0kHz - 4kHz: Voiceband Services
* 4kHz - 28.875kHz: Unused buffer area
* 28.875kHz - 138kHz: Used for upstream transmission,
* 138kHz - 1104kHz: Used for downstream transmission.

Note that the upstream frequency range is much smaller than the downstream frequency range. This is the asymmetric nature of ADSL; in true DSL, the upstream and downstream frequency spreads are equal. Also note that ADSL is a full duplex technology, which means that signals can be travelling in opposite directions at the same time, on a single wire. An easy way to conceptualize the use of the frequency ranges is to imagine the ranges as "pipes" through which the various signals travel like water. The larger the pipe, the more water can travel through it.

The two main frequency ranges are further subdivided into smaller units, called channels, each of which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the channels on the line to establish which ones have the best signal-to-noise ration, a measure of how much interference exists in that channel versus how strong the ADSL signal is. Interference on a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antennae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of available bandwidth decreases with each unusable channel.

 

==The Future of ADSL==

===The Growth of ADSL===
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of Highspeed Internet. Due to the ease of installation, and the fact that it utilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fibber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away, and a new one is installed less than 1km distant).

===New Devices===
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
Up until recently, when someone subscribed for ADSL service, they would receive an ADSL modem from the ISP. This modem would then be attached to the phone line and the subscriber's computer, providing Internet service. If the subscriber wished to use more than one computer with the service, he would be forced to purchase a router. Lately, ISPs have begun to distribute devices where are being termed "Home Gateways". These devices incorporate the ADSL modem, a 4 port home router, and a wireless access point into one compact form factor. With home networking on the rise, these devices are expected to be extremely popular with home users as they will limit the clutter required for a home network, and centralize control of all aspects of the network into one device.

===Competition===
Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the successor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widespread adoption in Japan and South Korea where it is the predominant high speed Internet technology.

==See Also==
[[Wireless Network Security]] 
[[WiMAX]] 
[[Mesh Networking]] 
[[Designing a Small Business Intranet]] 
[[Internet Cookies and Confidentiality]] 

==References==
# ADSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/Adsl http://en.wikipedia.org/wiki/Adsl]
# Tyson, Jeff. ''How VDSL Works''. How Stuff Works.com. Retrieved April 7, 2008 from [http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
# Volf, Zahy. Anita Demayo. Roei Limoni. ''ADSL''. RAD University. Retrieved April 7, 2008 from [http://www2.rad.com/networks/2005/adsl/main.htm http://www2.rad.com/networks/2005/adsl/main.htm]
# Hamill, Hugh et all. ''Asymmetric Digital Subscriber Line''. Retrieved April 7, 2008 from [http://www.esatclear.ie/~aodhoh/adsl/report.html http://www.esatclear.ie/~aodhoh/adsl/report.html]
# VDSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

==External Links==
* [http://http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
* [http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]
* [http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 22:12, 13 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T02:12:59Z

Johnstfd:

ADSL (Asymmetric Digital Subscriber Line) is one of the leading technologies for providing high-speed Internet service to subscribers. ADSL is a variant of DSL, and there exists a common misconception that the A stands for Asynchronous. This is incorrect, as ADSL is a synchronous service. It is, however, asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
===History===
Historically, Internet was served to people's homes through the use of voiceband data modems connect to the existing copper telephone line network. This network consists of twisted pair copper wires which run from a subscriber's home back to the telephone company's central office. The voiceband data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in harmony with a voice signal.

Traditionally, when ADSL was run to a home, a whole home splitter was installed at the demarcation point, the point where the phone line enters the home from the street. The splitter would filter all existing phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and install the device. Most ISPs have now adopted a much more passive stance wherein they ship the subscriber a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degradation of service for the consumer if they have more than 5 voiceband devices in their home. The reason for this is that the branching of the various phone lines causes reflections which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

===The Technology===
ADSL differs from standard DSL in that the data flow is asymmetric; data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are placed to Internet servers for websites or files, which are then downloaded to the subscriber's PC. Requests are much smaller than the files and websites they lead to, so there is little need for large upstream transmission capability. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, only recently has its bandwidth been fully used. The advent of technologies such as BitTorrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

 
==Functionality==
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
===Physical Setup===
The physical setup of the ADSL system is fairly symmetrical. The core of the setup is the DSLAM (Digital Subscriber Link Access Multiplexer), a device which is responsible for intermixing the voice and data signals on the downstream side of the connection, and for separating out the voice from the data signal on the upstream side.
On the upstream side, once the voice signal has been removed from the line, it is passed on to the phone company's telephony network. The data signal is passed onto the ISP's Internet backbone.
On the downstream side, the DSLAM combines the voice and data signals coming from the phone network and the Internet, and transmits them down the twister pair copper line to the subscriber's home. There is a physical distance restriction imposed here, of about 5km. This is the maximum distance that a signal from a DSLAM can travel without degradation. Beyond this point, Internet service may be intermittent, or slow, or just not possible. For this reason, ISPs will not provide ADSL to people living outside of the 5km service area of a DSLAM.
After the signal arrives at the subscriber's home, one of two situations is possible. Either a whole home splitter is installed, which filters the ADSL signal from the home's phone lines, and passes it along an unfiltered line to an ADSL modem, or the subscriber has installed microfilters on their voiceband devices, filtering out the ADSL at the wall jacks. Either way, the signal must now pass into an ADSL high speed modem, which will interpret the signal, and communicate with either a computer, or a router, providing Internet access. ADSL modems are power hungry devices and require their own power source; there is no way to incorporate them into a home computer system the way that voiceband modems have been.

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. The frequencies within the copper line are broken down as follows:
* 0kHz - 4kHz: Voiceband Services
* 4kHz - 28.875kHz: Unused buffer area
* 28.875kHz - 138kHz: Used for upstream transmission,
* 138kHz - 1104kHz: Used for downstream transmission.

Note that the upstream frequency range is much smaller than the downstream frequency range. This is the asymmetric nature of ADSL; in true DSL, the upstream and downstream frequency spreads are equal. Also note that ADSL is a full duplex technology, which means that signals can be travelling in opposite directions at the same time, on a single wire. An easy way to conceptualize the use of the frequency ranges is to imagine the ranges as "pipes" through which the various signals travel like water. The larger the pipe, the more water can travel through it.

The two main frequency ranges are further subdivided into smaller units, called channels, each of which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the channels on the line to establish which ones have the best signal-to-noise ration, a measure of how much interference exists in that channel versus how strong the ADSL signal is. Interference on a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antennae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of available bandwidth decreases with each unusable channel.

 

==The Future of ADSL==

===The Growth of ADSL===
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of Highspeed Internet. Due to the ease of installation, and the fact that it utilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fibber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away, and a new one is installed less than 1km distant).

===New Devices===
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
Up until recently, when someone subscribed for ADSL service, they would receive an ADSL modem from the ISP. This modem would then be attached to the phone line and the subscriber's computer, providing Internet service. If the subscriber wished to use more than one computer with the service, he would be forced to purchase a router. Lately, ISPs have begun to distribute devices where are being termed "Home Gateways". These devices incorporate the ADSL modem, a 4 port home router, and a wireless access point into one compact form factor. With home networking on the rise, these devices are expected to be extremely popular with home users as they will limit the clutter required for a home network, and centralize control of all aspects of the network into one device.

===Competition===
Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the successor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widespread adoption in Japan and South Korea where it is the predominant high speed Internet technology.

==See Also==
[[Wireless Network Security]] 
[[WiMAX]] 
[[Mesh Networking]] 
[[Designing a Small Business Intranet]] 
[[Internet Cookies and Confidentiality]] 
 

==References==
# ADSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/Adsl http://en.wikipedia.org/wiki/Adsl]
# Tyson, Jeff. ''How VDSL Works''. How Stuff Works.com. Retrieved April 7, 2008 from [http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
# Volf, Zahy. Anita Demayo. Roei Limoni. ''ADSL''. RAD University. Retrieved April 7, 2008 from [http://www2.rad.com/networks/2005/adsl/main.htm http://www2.rad.com/networks/2005/adsl/main.htm]
# Hamill, Hugh et all. ''Asymmetric Digital Subscriber Line''. Retrieved April 7, 2008 from [http://www.esatclear.ie/~aodhoh/adsl/report.html http://www.esatclear.ie/~aodhoh/adsl/report.html]
# VDSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

==External Links==
* [http://http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
* [http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]
* [http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 22:12, 13 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T02:12:23Z

Johnstfd:

ADSL (Asymmetric Digital Subscriber Line) is one of the leading technologies for providing high-speed Internet service to subscribers. ADSL is a variant of DSL, and there exists a common misconception that the A stands for Asynchronous. This is incorrect, as ADSL is a synchronous service. It is, however, asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
===History===
Historically, Internet was served to people's homes through the use of voiceband data modems connect to the existing copper telephone line network. This network consists of twisted pair copper wires which run from a subscriber's home back to the telephone company's central office. The voiceband data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in harmony with a voice signal.

Traditionally, when ADSL was run to a home, a whole home splitter was installed at the demarcation point, the point where the phone line enters the home from the street. The splitter would filter all existing phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and install the device. Most ISPs have now adopted a much more passive stance wherein they ship the subscriber a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degradation of service for the consumer if they have more than 5 voiceband devices in their home. The reason for this is that the branching of the various phone lines causes reflections which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

===The Technology===
ADSL differs from standard DSL in that the data flow is asymmetric; data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are placed to Internet servers for websites or files, which are then downloaded to the subscriber's PC. Requests are much smaller than the files and websites they lead to, so there is little need for large upstream transmission capability. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, only recently has its bandwidth been fully used. The advent of technologies such as BitTorrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

 
==Functionality==
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
===Physical Setup===
The physical setup of the ADSL system is fairly symmetrical. The core of the setup is the DSLAM (Digital Subscriber Link Access Multiplexer), a device which is responsible for intermixing the voice and data signals on the downstream side of the connection, and for separating out the voice from the data signal on the upstream side.
On the upstream side, once the voice signal has been removed from the line, it is passed on to the phone company's telephony network. The data signal is passed onto the ISP's Internet backbone.
On the downstream side, the DSLAM combines the voice and data signals coming from the phone network and the Internet, and transmits them down the twister pair copper line to the subscriber's home. There is a physical distance restriction imposed here, of about 5km. This is the maximum distance that a signal from a DSLAM can travel without degradation. Beyond this point, Internet service may be intermittent, or slow, or just not possible. For this reason, ISPs will not provide ADSL to people living outside of the 5km service area of a DSLAM.
After the signal arrives at the subscriber's home, one of two situations is possible. Either a whole home splitter is installed, which filters the ADSL signal from the home's phone lines, and passes it along an unfiltered line to an ADSL modem, or the subscriber has installed microfilters on their voiceband devices, filtering out the ADSL at the wall jacks. Either way, the signal must now pass into an ADSL high speed modem, which will interpret the signal, and communicate with either a computer, or a router, providing Internet access. ADSL modems are power hungry devices and require their own power source; there is no way to incorporate them into a home computer system the way that voiceband modems have been.

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. The frequencies within the copper line are broken down as follows:
* 0kHz - 4kHz: Voiceband Services
* 4kHz - 28.875kHz: Unused buffer area
* 28.875kHz - 138kHz: Used for upstream transmission,
* 138kHz - 1104kHz: Used for downstream transmission.

Note that the upstream frequency range is much smaller than the downstream frequency range. This is the asymmetric nature of ADSL; in true DSL, the upstream and downstream frequency spreads are equal. Also note that ADSL is a full duplex technology, which means that signals can be travelling in opposite directions at the same time, on a single wire. An easy way to conceptualize the use of the frequency ranges is to imagine the ranges as "pipes" through which the various signals travel like water. The larger the pipe, the more water can travel through it.

The two main frequency ranges are further subdivided into smaller units, called channels, each of which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the channels on the line to establish which ones have the best signal-to-noise ration, a measure of how much interference exists in that channel versus how strong the ADSL signal is. Interference on a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antennae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of available bandwidth decreases with each unusable channel.

 

==The Future of ADSL==

===The Growth of ADSL===
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of Highspeed Internet. Due to the ease of installation, and the fact that it utilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fibber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away, and a new one is installed less than 1km distant).

===New Devices===
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
Up until recently, when someone subscribed for ADSL service, they would receive an ADSL modem from the ISP. This modem would then be attached to the phone line and the subscriber's computer, providing Internet service. If the subscriber wished to use more than one computer with the service, he would be forced to purchase a router. Lately, ISPs have begun to distribute devices where are being termed "Home Gateways". These devices incorporate the ADSL modem, a 4 port home router, and a wireless access point into one compact form factor. With home networking on the rise, these devices are expected to be extremely popular with home users as they will limit the clutter required for a home network, and centralize control of all aspects of the network into one device.

===Competition===
Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the successor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widespread adoption in Japan and South Korea where it is the predominant high speed Internet technology.

==See Also==
[[Wireless Network Security]] 
[[WiMAX]] 
[[Mesh Networking]] 
[[Designing a Small Business Intranet]] 
[[Internet Cookies and Confidentiality]] 
 

==References==
# ADSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/Adsl http://en.wikipedia.org/wiki/Adsl]
# Tyson, Jeff. ''How VDSL Works''. How Stuff Works.com. Retrieved April 7, 2008 from [http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
# Volf, Zahy. Anita Demayo. Roei Limoni. ''ADSL''. RAD University. Retrieved April 7, 2008 from [http://www2.rad.com/networks/2005/adsl/main.htm http://www2.rad.com/networks/2005/adsl/main.htm]
# Hamill, Hugh et all. ''Asymmetric Digital Subscriber Line''. Retrieved April 7, 2008 from [http://www.esatclear.ie/~aodhoh/adsl/report.html http://www.esatclear.ie/~aodhoh/adsl/report.html]
# VDSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

==External Links==
[http://http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
[http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]
[http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 22:12, 13 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T02:11:50Z

Johnstfd: /* References */

ADSL (Asymmetric Digital Subscriber Line) is one of the leading technologies for providing high-speed Internet service to subscribers. ADSL is a variant of DSL, and there exists a common misconception that the A stands for Asynchronous. This is incorrect, as ADSL is a synchronous service. It is, however, asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
===History===
Historically, Internet was served to people's homes through the use of voiceband data modems connect to the existing copper telephone line network. This network consists of twisted pair copper wires which run from a subscriber's home back to the telephone company's central office. The voiceband data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in harmony with a voice signal.

Traditionally, when ADSL was run to a home, a whole home splitter was installed at the demarcation point, the point where the phone line enters the home from the street. The splitter would filter all existing phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and install the device. Most ISPs have now adopted a much more passive stance wherein they ship the subscriber a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degradation of service for the consumer if they have more than 5 voiceband devices in their home. The reason for this is that the branching of the various phone lines causes reflections which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

===The Technology===
ADSL differs from standard DSL in that the data flow is asymmetric; data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are placed to Internet servers for websites or files, which are then downloaded to the subscriber's PC. Requests are much smaller than the files and websites they lead to, so there is little need for large upstream transmission capability. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, only recently has its bandwidth been fully used. The advent of technologies such as BitTorrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

 
==Functionality==
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
===Physical Setup===
The physical setup of the ADSL system is fairly symmetrical. The core of the setup is the DSLAM (Digital Subscriber Link Access Multiplexer), a device which is responsible for intermixing the voice and data signals on the downstream side of the connection, and for separating out the voice from the data signal on the upstream side.
On the upstream side, once the voice signal has been removed from the line, it is passed on to the phone company's telephony network. The data signal is passed onto the ISP's Internet backbone.
On the downstream side, the DSLAM combines the voice and data signals coming from the phone network and the Internet, and transmits them down the twister pair copper line to the subscriber's home. There is a physical distance restriction imposed here, of about 5km. This is the maximum distance that a signal from a DSLAM can travel without degradation. Beyond this point, Internet service may be intermittent, or slow, or just not possible. For this reason, ISPs will not provide ADSL to people living outside of the 5km service area of a DSLAM.
After the signal arrives at the subscriber's home, one of two situations is possible. Either a whole home splitter is installed, which filters the ADSL signal from the home's phone lines, and passes it along an unfiltered line to an ADSL modem, or the subscriber has installed microfilters on their voiceband devices, filtering out the ADSL at the wall jacks. Either way, the signal must now pass into an ADSL high speed modem, which will interpret the signal, and communicate with either a computer, or a router, providing Internet access. ADSL modems are power hungry devices and require their own power source; there is no way to incorporate them into a home computer system the way that voiceband modems have been.

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. The frequencies within the copper line are broken down as follows:
* 0kHz - 4kHz: Voiceband Services
* 4kHz - 28.875kHz: Unused buffer area
* 28.875kHz - 138kHz: Used for upstream transmission,
* 138kHz - 1104kHz: Used for downstream transmission.

Note that the upstream frequency range is much smaller than the downstream frequency range. This is the asymmetric nature of ADSL; in true DSL, the upstream and downstream frequency spreads are equal. Also note that ADSL is a full duplex technology, which means that signals can be travelling in opposite directions at the same time, on a single wire. An easy way to conceptualize the use of the frequency ranges is to imagine the ranges as "pipes" through which the various signals travel like water. The larger the pipe, the more water can travel through it.

The two main frequency ranges are further subdivided into smaller units, called channels, each of which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the channels on the line to establish which ones have the best signal-to-noise ration, a measure of how much interference exists in that channel versus how strong the ADSL signal is. Interference on a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antennae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of available bandwidth decreases with each unusable channel.

 

==The Future of ADSL==

===The Growth of ADSL===
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of Highspeed Internet. Due to the ease of installation, and the fact that it utilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fibber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away, and a new one is installed less than 1km distant).

===New Devices===
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
Up until recently, when someone subscribed for ADSL service, they would receive an ADSL modem from the ISP. This modem would then be attached to the phone line and the subscriber's computer, providing Internet service. If the subscriber wished to use more than one computer with the service, he would be forced to purchase a router. Lately, ISPs have begun to distribute devices where are being termed "Home Gateways". These devices incorporate the ADSL modem, a 4 port home router, and a wireless access point into one compact form factor. With home networking on the rise, these devices are expected to be extremely popular with home users as they will limit the clutter required for a home network, and centralize control of all aspects of the network into one device.

===Competition===
Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the successor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widespread adoption in Japan and South Korea where it is the predominant high speed Internet technology.

==See Also==
[[Wireless Network Security]] 
[[WiMAX]] 
[[Mesh Networking]] 
[[Designing a Small Business Intranet]] 
[[Internet Cookies and Confidentiality]] 
 

==References==
# ADSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/Adsl http://en.wikipedia.org/wiki/Adsl]
# Tyson, Jeff. ''How VDSL Works''. How Stuff Works.com. Retrieved April 7, 2008 from [http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
# Volf, Zahy. Anita Demayo. Roei Limoni. ''ADSL''. RAD University. Retrieved April 7, 2008 from [http://www2.rad.com/networks/2005/adsl/main.htm http://www2.rad.com/networks/2005/adsl/main.htm]
# Hamill, Hugh et all. ''Asymmetric Digital Subscriber Line''. Retrieved April 7, 2008 from [http://www.esatclear.ie/~aodhoh/adsl/report.html http://www.esatclear.ie/~aodhoh/adsl/report.html]
# VDSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

==External Links==
[http://http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
[http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]
[http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 22:09, 13 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T02:11:18Z

Johnstfd:

ADSL (Asymmetric Digital Subscriber Line) is one of the leading technologies for providing high-speed Internet service to subscribers. ADSL is a variant of DSL, and there exists a common misconception that the A stands for Asynchronous. This is incorrect, as ADSL is a synchronous service. It is, however, asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
===History===
Historically, Internet was served to people's homes through the use of voiceband data modems connect to the existing copper telephone line network. This network consists of twisted pair copper wires which run from a subscriber's home back to the telephone company's central office. The voiceband data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in harmony with a voice signal.

Traditionally, when ADSL was run to a home, a whole home splitter was installed at the demarcation point, the point where the phone line enters the home from the street. The splitter would filter all existing phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and install the device. Most ISPs have now adopted a much more passive stance wherein they ship the subscriber a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degradation of service for the consumer if they have more than 5 voiceband devices in their home. The reason for this is that the branching of the various phone lines causes reflections which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

===The Technology===
ADSL differs from standard DSL in that the data flow is asymmetric; data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are placed to Internet servers for websites or files, which are then downloaded to the subscriber's PC. Requests are much smaller than the files and websites they lead to, so there is little need for large upstream transmission capability. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, only recently has its bandwidth been fully used. The advent of technologies such as BitTorrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

 
==Functionality==
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
===Physical Setup===
The physical setup of the ADSL system is fairly symmetrical. The core of the setup is the DSLAM (Digital Subscriber Link Access Multiplexer), a device which is responsible for intermixing the voice and data signals on the downstream side of the connection, and for separating out the voice from the data signal on the upstream side.
On the upstream side, once the voice signal has been removed from the line, it is passed on to the phone company's telephony network. The data signal is passed onto the ISP's Internet backbone.
On the downstream side, the DSLAM combines the voice and data signals coming from the phone network and the Internet, and transmits them down the twister pair copper line to the subscriber's home. There is a physical distance restriction imposed here, of about 5km. This is the maximum distance that a signal from a DSLAM can travel without degradation. Beyond this point, Internet service may be intermittent, or slow, or just not possible. For this reason, ISPs will not provide ADSL to people living outside of the 5km service area of a DSLAM.
After the signal arrives at the subscriber's home, one of two situations is possible. Either a whole home splitter is installed, which filters the ADSL signal from the home's phone lines, and passes it along an unfiltered line to an ADSL modem, or the subscriber has installed microfilters on their voiceband devices, filtering out the ADSL at the wall jacks. Either way, the signal must now pass into an ADSL high speed modem, which will interpret the signal, and communicate with either a computer, or a router, providing Internet access. ADSL modems are power hungry devices and require their own power source; there is no way to incorporate them into a home computer system the way that voiceband modems have been.

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. The frequencies within the copper line are broken down as follows:
* 0kHz - 4kHz: Voiceband Services
* 4kHz - 28.875kHz: Unused buffer area
* 28.875kHz - 138kHz: Used for upstream transmission,
* 138kHz - 1104kHz: Used for downstream transmission.

Note that the upstream frequency range is much smaller than the downstream frequency range. This is the asymmetric nature of ADSL; in true DSL, the upstream and downstream frequency spreads are equal. Also note that ADSL is a full duplex technology, which means that signals can be travelling in opposite directions at the same time, on a single wire. An easy way to conceptualize the use of the frequency ranges is to imagine the ranges as "pipes" through which the various signals travel like water. The larger the pipe, the more water can travel through it.

The two main frequency ranges are further subdivided into smaller units, called channels, each of which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the channels on the line to establish which ones have the best signal-to-noise ration, a measure of how much interference exists in that channel versus how strong the ADSL signal is. Interference on a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antennae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of available bandwidth decreases with each unusable channel.

 

==The Future of ADSL==

===The Growth of ADSL===
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of Highspeed Internet. Due to the ease of installation, and the fact that it utilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fibber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away, and a new one is installed less than 1km distant).

===New Devices===
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
Up until recently, when someone subscribed for ADSL service, they would receive an ADSL modem from the ISP. This modem would then be attached to the phone line and the subscriber's computer, providing Internet service. If the subscriber wished to use more than one computer with the service, he would be forced to purchase a router. Lately, ISPs have begun to distribute devices where are being termed "Home Gateways". These devices incorporate the ADSL modem, a 4 port home router, and a wireless access point into one compact form factor. With home networking on the rise, these devices are expected to be extremely popular with home users as they will limit the clutter required for a home network, and centralize control of all aspects of the network into one device.

===Competition===
Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the successor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widespread adoption in Japan and South Korea where it is the predominant high speed Internet technology.

==See Also==
[[Wireless Network Security]] 
[[WiMAX]] 
[[Mesh Networking]] 
[[Designing a Small Business Intranet]] 
[[Internet Cookies and Confidentiality]] 
 

==References==
# ADSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/Adsl]
# Tyson, Jeff. ''How VDSL Works''. How Stuff Works.com. Retrieved April 7, 2008 from [http://electronics.howstuffworks.com/vdsl1.htm]
# Volf, Zahy. Anita Demayo. Roei Limoni. ''ADSL''. RAD University. Retrieved April 7, 2008 from [http://www2.rad.com/networks/2005/adsl/main.htm]
# Hamill, Hugh et all. ''Asymmetric Digital Subscriber Line''. Retrieved April 7, 2008 from [http://www.esatclear.ie/~aodhoh/adsl/report.html]
# VDSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/VDSL]

==External Links==
[http://http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
[http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]
[http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 22:09, 13 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T02:09:54Z

Johnstfd:

ADSL (Asymmetric Digital Subscriber Line) is one of the leading technologies for providing high-speed Internet service to subscribers. ADSL is a variant of DSL, and there exists a common misconception that the A stands for Asynchronous. This is incorrect, as ADSL is a synchronous service. It is, however, asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
===History===
Historically, Internet was served to people's homes through the use of voiceband data modems connect to the existing copper telephone line network. This network consists of twisted pair copper wires which run from a subscriber's home back to the telephone company's central office. The voiceband data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in harmony with a voice signal.

Traditionally, when ADSL was run to a home, a whole home splitter was installed at the demarcation point, the point where the phone line enters the home from the street. The splitter would filter all existing phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and install the device. Most ISPs have now adopted a much more passive stance wherein they ship the subscriber a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degradation of service for the consumer if they have more than 5 voiceband devices in their home. The reason for this is that the branching of the various phone lines causes reflections which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

===The Technology===
ADSL differs from standard DSL in that the data flow is asymmetric; data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are placed to Internet servers for websites or files, which are then downloaded to the subscriber's PC. Requests are much smaller than the files and websites they lead to, so there is little need for large upstream transmission capability. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, only recently has its bandwidth been fully used. The advent of technologies such as BitTorrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

 
==Functionality==
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
===Physical Setup===
The physical setup of the ADSL system is fairly symmetrical. The core of the setup is the DSLAM (Digital Subscriber Link Access Multiplexer), a device which is responsible for intermixing the voice and data signals on the downstream side of the connection, and for separating out the voice from the data signal on the upstream side.
On the upstream side, once the voice signal has been removed from the line, it is passed on to the phone company's telephony network. The data signal is passed onto the ISP's Internet backbone.
On the downstream side, the DSLAM combines the voice and data signals coming from the phone network and the Internet, and transmits them down the twister pair copper line to the subscriber's home. There is a physical distance restriction imposed here, of about 5km. This is the maximum distance that a signal from a DSLAM can travel without degradation. Beyond this point, Internet service may be intermittent, or slow, or just not possible. For this reason, ISPs will not provide ADSL to people living outside of the 5km service area of a DSLAM.
After the signal arrives at the subscriber's home, one of two situations is possible. Either a whole home splitter is installed, which filters the ADSL signal from the home's phone lines, and passes it along an unfiltered line to an ADSL modem, or the subscriber has installed microfilters on their voiceband devices, filtering out the ADSL at the wall jacks. Either way, the signal must now pass into an ADSL high speed modem, which will interpret the signal, and communicate with either a computer, or a router, providing Internet access. ADSL modems are power hungry devices and require their own power source; there is no way to incorporate them into a home computer system the way that voiceband modems have been.

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. The frequencies within the copper line are broken down as follows:
* 0kHz - 4kHz: Voiceband Services
* 4kHz - 28.875kHz: Unused buffer area
* 28.875kHz - 138kHz: Used for upstream transmission,
* 138kHz - 1104kHz: Used for downstream transmission.

Note that the upstream frequency range is much smaller than the downstream frequency range. This is the asymmetric nature of ADSL; in true DSL, the upstream and downstream frequency spreads are equal. Also note that ADSL is a full duplex technology, which means that signals can be travelling in opposite directions at the same time, on a single wire. An easy way to conceptualize the use of the frequency ranges is to imagine the ranges as "pipes" through which the various signals travel like water. The larger the pipe, the more water can travel through it.

The two main frequency ranges are further subdivided into smaller units, called channels, each of which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the channels on the line to establish which ones have the best signal-to-noise ration, a measure of how much interference exists in that channel versus how strong the ADSL signal is. Interference on a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antennae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of available bandwidth decreases with each unusable channel.

 

==The Future of ADSL==

===The Growth of ADSL===
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of Highspeed Internet. Due to the ease of installation, and the fact that it utilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fibber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away, and a new one is installed less than 1km distant).

===New Devices===
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
Up until recently, when someone subscribed for ADSL service, they would receive an ADSL modem from the ISP. This modem would then be attached to the phone line and the subscriber's computer, providing Internet service. If the subscriber wished to use more than one computer with the service, he would be forced to purchase a router. Lately, ISPs have begun to distribute devices where are being termed "Home Gateways". These devices incorporate the ADSL modem, a 4 port home router, and a wireless access point into one compact form factor. With home networking on the rise, these devices are expected to be extremely popular with home users as they will limit the clutter required for a home network, and centralize control of all aspects of the network into one device.

===Competition===
Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the successor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widespread adoption in Japan and South Korea where it is the predominant high speed Internet technology.

==See Also==
[[Wireless Network Security]] 
[[WiMAX]] 
[[Mesh Networking]] 
[[Designing a Small Business Intranet]] 
[[Internet Cookies and Confidentiality]] 
 

==References==
# ADSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
# Tyson, Jeff. ''How VDSL Works''. How Stuff Works.com. Retrieved April 7, 2008 from [http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
# Volf, Zahy. Anita Demayo. Roei Limoni. ''ADSL''. RAD University. Retrieved April 7, 2008 from [http://www2.rad.com/networks/2005/adsl/main.htm]
# Hamill, Hugh et all. ''Asymmetric Digital Subscriber Line''. Retrieved April 7, 2008 from [http://www.esatclear.ie/~aodhoh/adsl/report.html]
# VDSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

==External Links==
[http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 22:09, 13 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T02:09:31Z

Johnstfd:

ADSL (Asymmetric Digital Subscriber Line) is one of the leading technologies for providing high-speed Internet service to subscribers. ADSL is a variant of DSL, and there exists a common misconception that the A stands for Asynchronous. This is incorrect, as ADSL is a synchronous service. It is, however, asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
===History===
Historically, Internet was served to people's homes through the use of voiceband data modems connect to the existing copper telephone line network. This network consists of twisted pair copper wires which run from a subscriber's home back to the telephone company's central office. The voiceband data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in harmony with a voice signal.

Traditionally, when ADSL was run to a home, a whole home splitter was installed at the demarcation point, the point where the phone line enters the home from the street. The splitter would filter all existing phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and install the device. Most ISPs have now adopted a much more passive stance wherein they ship the subscriber a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degradation of service for the consumer if they have more than 5 voiceband devices in their home. The reason for this is that the branching of the various phone lines causes reflections which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

===The Technology===
ADSL differs from standard DSL in that the data flow is asymmetric; data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are placed to Internet servers for websites or files, which are then downloaded to the subscriber's PC. Requests are much smaller than the files and websites they lead to, so there is little need for large upstream transmission capability. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, only recently has its bandwidth been fully used. The advent of technologies such as BitTorrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

 
==Functionality==
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
===Physical Setup===
The physical setup of the ADSL system is fairly symmetrical. The core of the setup is the DSLAM (Digital Subscriber Link Access Multiplexer), a device which is responsible for intermixing the voice and data signals on the downstream side of the connection, and for separating out the voice from the data signal on the upstream side.
On the upstream side, once the voice signal has been removed from the line, it is passed on to the phone company's telephony network. The data signal is passed onto the ISP's Internet backbone.
On the downstream side, the DSLAM combines the voice and data signals coming from the phone network and the Internet, and transmits them down the twister pair copper line to the subscriber's home. There is a physical distance restriction imposed here, of about 5km. This is the maximum distance that a signal from a DSLAM can travel without degradation. Beyond this point, Internet service may be intermittent, or slow, or just not possible. For this reason, ISPs will not provide ADSL to people living outside of the 5km service area of a DSLAM.
After the signal arrives at the subscriber's home, one of two situations is possible. Either a whole home splitter is installed, which filters the ADSL signal from the home's phone lines, and passes it along an unfiltered line to an ADSL modem, or the subscriber has installed microfilters on their voiceband devices, filtering out the ADSL at the wall jacks. Either way, the signal must now pass into an ADSL high speed modem, which will interpret the signal, and communicate with either a computer, or a router, providing Internet access. ADSL modems are power hungry devices and require their own power source; there is no way to incorporate them into a home computer system the way that voiceband modems have been.

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. The frequencies within the copper line are broken down as follows:
* 0kHz - 4kHz: Voiceband Services
* 4kHz - 28.875kHz: Unused buffer area
* 28.875kHz - 138kHz: Used for upstream transmission,
* 138kHz - 1104kHz: Used for downstream transmission.

Note that the upstream frequency range is much smaller than the downstream frequency range. This is the asymmetric nature of ADSL; in true DSL, the upstream and downstream frequency spreads are equal. Also note that ADSL is a full duplex technology, which means that signals can be travelling in opposite directions at the same time, on a single wire. An easy way to conceptualize the use of the frequency ranges is to imagine the ranges as "pipes" through which the various signals travel like water. The larger the pipe, the more water can travel through it.

The two main frequency ranges are further subdivided into smaller units, called channels, each of which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the channels on the line to establish which ones have the best signal-to-noise ration, a measure of how much interference exists in that channel versus how strong the ADSL signal is. Interference on a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antennae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of available bandwidth decreases with each unusable channel.

 

==The Future of ADSL==

===The Growth of ADSL===
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of Highspeed Internet. Due to the ease of installation, and the fact that it utilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fibber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away, and a new one is installed less than 1km distant).

===New Devices===
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
Up until recently, when someone subscribed for ADSL service, they would receive an ADSL modem from the ISP. This modem would then be attached to the phone line and the subscriber's computer, providing Internet service. If the subscriber wished to use more than one computer with the service, he would be forced to purchase a router. Lately, ISPs have begun to distribute devices where are being termed "Home Gateways". These devices incorporate the ADSL modem, a 4 port home router, and a wireless access point into one compact form factor. With home networking on the rise, these devices are expected to be extremely popular with home users as they will limit the clutter required for a home network, and centralize control of all aspects of the network into one device.

===Competition===
Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the successor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widespread adoption in Japan and South Korea where it is the predominant high speed Internet technology.

==See Also==
[[Wireless Network Security]] 
[[WiMAX]] 
[[Mesh Networking]] 
[[Designing a Small Business Intranet]] 
[[Internet Cookies and Confidentiality]] 
 

==References==
# ADSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
# Tyson, Jeff. ''How VDSL Works''. How Stuff Works.com. Retrieved April 7, 2008 from [http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
# Volf, Zahy. Anita Demayo. Roei Limoni. ''ADSL''. RAD University. Retrieved April 7, 2008 from [http://www2.rad.com/networks/2005/adsl/main.htm]
# Hamill, Hugh et all. ''Asymmetric Digital Subscriber Line''. Retrieved April 7, 2008 from [http://www.esatclear.ie/~aodhoh/adsl/report.html]
# VDSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

==External Links==
[http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 10:47, 9 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T02:09:11Z

Johnstfd: /* References */

ADSL (Asymmetric Digital Subscriber Line) is one of the leading technologies for providing high-speed Internet service to subscribers. ADSL is a variant of DSL, and there exists a common misconception that the A stands for Asynchronous. This is incorrect, as ADSL is a synchronous service. It is, however, asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

 
==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
===History===
Historically, Internet was served to people's homes through the use of voiceband data modems connect to the existing copper telephone line network. This network consists of twisted pair copper wires which run from a subscriber's home back to the telephone company's central office. The voiceband data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in harmony with a voice signal.

Traditionally, when ADSL was run to a home, a whole home splitter was installed at the demarcation point, the point where the phone line enters the home from the street. The splitter would filter all existing phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and install the device. Most ISPs have now adopted a much more passive stance wherein they ship the subscriber a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degradation of service for the consumer if they have more than 5 voiceband devices in their home. The reason for this is that the branching of the various phone lines causes reflections which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

===The Technology===
ADSL differs from standard DSL in that the data flow is asymmetric; data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are placed to Internet servers for websites or files, which are then downloaded to the subscriber's PC. Requests are much smaller than the files and websites they lead to, so there is little need for large upstream transmission capability. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, only recently has its bandwidth been fully used. The advent of technologies such as BitTorrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

 
==Functionality==
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
===Physical Setup===
The physical setup of the ADSL system is fairly symmetrical. The core of the setup is the DSLAM (Digital Subscriber Link Access Multiplexer), a device which is responsible for intermixing the voice and data signals on the downstream side of the connection, and for separating out the voice from the data signal on the upstream side.
On the upstream side, once the voice signal has been removed from the line, it is passed on to the phone company's telephony network. The data signal is passed onto the ISP's Internet backbone.
On the downstream side, the DSLAM combines the voice and data signals coming from the phone network and the Internet, and transmits them down the twister pair copper line to the subscriber's home. There is a physical distance restriction imposed here, of about 5km. This is the maximum distance that a signal from a DSLAM can travel without degradation. Beyond this point, Internet service may be intermittent, or slow, or just not possible. For this reason, ISPs will not provide ADSL to people living outside of the 5km service area of a DSLAM.
After the signal arrives at the subscriber's home, one of two situations is possible. Either a whole home splitter is installed, which filters the ADSL signal from the home's phone lines, and passes it along an unfiltered line to an ADSL modem, or the subscriber has installed microfilters on their voiceband devices, filtering out the ADSL at the wall jacks. Either way, the signal must now pass into an ADSL high speed modem, which will interpret the signal, and communicate with either a computer, or a router, providing Internet access. ADSL modems are power hungry devices and require their own power source; there is no way to incorporate them into a home computer system the way that voiceband modems have been.

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. The frequencies within the copper line are broken down as follows:
* 0kHz - 4kHz: Voiceband Services
* 4kHz - 28.875kHz: Unused buffer area
* 28.875kHz - 138kHz: Used for upstream transmission,
* 138kHz - 1104kHz: Used for downstream transmission.

Note that the upstream frequency range is much smaller than the downstream frequency range. This is the asymmetric nature of ADSL; in true DSL, the upstream and downstream frequency spreads are equal. Also note that ADSL is a full duplex technology, which means that signals can be travelling in opposite directions at the same time, on a single wire. An easy way to conceptualize the use of the frequency ranges is to imagine the ranges as "pipes" through which the various signals travel like water. The larger the pipe, the more water can travel through it.

The two main frequency ranges are further subdivided into smaller units, called channels, each of which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the channels on the line to establish which ones have the best signal-to-noise ration, a measure of how much interference exists in that channel versus how strong the ADSL signal is. Interference on a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antennae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of available bandwidth decreases with each unusable channel.

 

==The Future of ADSL==

===The Growth of ADSL===
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of Highspeed Internet. Due to the ease of installation, and the fact that it utilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fibber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away, and a new one is installed less than 1km distant).

===New Devices===
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
Up until recently, when someone subscribed for ADSL service, they would receive an ADSL modem from the ISP. This modem would then be attached to the phone line and the subscriber's computer, providing Internet service. If the subscriber wished to use more than one computer with the service, he would be forced to purchase a router. Lately, ISPs have begun to distribute devices where are being termed "Home Gateways". These devices incorporate the ADSL modem, a 4 port home router, and a wireless access point into one compact form factor. With home networking on the rise, these devices are expected to be extremely popular with home users as they will limit the clutter required for a home network, and centralize control of all aspects of the network into one device.

===Competition===
Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the successor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widespread adoption in Japan and South Korea where it is the predominant high speed Internet technology.

 
==See Also==
[[Wireless Network Security]] 
[[WiMAX]] 
[[Mesh Networking]] 
[[Designing a Small Business Intranet]] 
[[Internet Cookies and Confidentiality]] 
 

==References==
# ADSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
# Tyson, Jeff. ''How VDSL Works''. How Stuff Works.com. Retrieved April 7, 2008 from [http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
# Volf, Zahy. Anita Demayo. Roei Limoni. ''ADSL''. RAD University. Retrieved April 7, 2008 from [http://www2.rad.com/networks/2005/adsl/main.htm]
# Hamill, Hugh et all. ''Asymmetric Digital Subscriber Line''. Retrieved April 7, 2008 from [http://www.esatclear.ie/~aodhoh/adsl/report.html]
# VDSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

==External Links==
[http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 10:47, 9 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T02:09:01Z

Johnstfd: /* References */

ADSL (Asymmetric Digital Subscriber Line) is one of the leading technologies for providing high-speed Internet service to subscribers. ADSL is a variant of DSL, and there exists a common misconception that the A stands for Asynchronous. This is incorrect, as ADSL is a synchronous service. It is, however, asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

 
==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
===History===
Historically, Internet was served to people's homes through the use of voiceband data modems connect to the existing copper telephone line network. This network consists of twisted pair copper wires which run from a subscriber's home back to the telephone company's central office. The voiceband data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in harmony with a voice signal.

Traditionally, when ADSL was run to a home, a whole home splitter was installed at the demarcation point, the point where the phone line enters the home from the street. The splitter would filter all existing phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and install the device. Most ISPs have now adopted a much more passive stance wherein they ship the subscriber a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degradation of service for the consumer if they have more than 5 voiceband devices in their home. The reason for this is that the branching of the various phone lines causes reflections which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

===The Technology===
ADSL differs from standard DSL in that the data flow is asymmetric; data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are placed to Internet servers for websites or files, which are then downloaded to the subscriber's PC. Requests are much smaller than the files and websites they lead to, so there is little need for large upstream transmission capability. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, only recently has its bandwidth been fully used. The advent of technologies such as BitTorrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

 
==Functionality==
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
===Physical Setup===
The physical setup of the ADSL system is fairly symmetrical. The core of the setup is the DSLAM (Digital Subscriber Link Access Multiplexer), a device which is responsible for intermixing the voice and data signals on the downstream side of the connection, and for separating out the voice from the data signal on the upstream side.
On the upstream side, once the voice signal has been removed from the line, it is passed on to the phone company's telephony network. The data signal is passed onto the ISP's Internet backbone.
On the downstream side, the DSLAM combines the voice and data signals coming from the phone network and the Internet, and transmits them down the twister pair copper line to the subscriber's home. There is a physical distance restriction imposed here, of about 5km. This is the maximum distance that a signal from a DSLAM can travel without degradation. Beyond this point, Internet service may be intermittent, or slow, or just not possible. For this reason, ISPs will not provide ADSL to people living outside of the 5km service area of a DSLAM.
After the signal arrives at the subscriber's home, one of two situations is possible. Either a whole home splitter is installed, which filters the ADSL signal from the home's phone lines, and passes it along an unfiltered line to an ADSL modem, or the subscriber has installed microfilters on their voiceband devices, filtering out the ADSL at the wall jacks. Either way, the signal must now pass into an ADSL high speed modem, which will interpret the signal, and communicate with either a computer, or a router, providing Internet access. ADSL modems are power hungry devices and require their own power source; there is no way to incorporate them into a home computer system the way that voiceband modems have been.

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. The frequencies within the copper line are broken down as follows:
* 0kHz - 4kHz: Voiceband Services
* 4kHz - 28.875kHz: Unused buffer area
* 28.875kHz - 138kHz: Used for upstream transmission,
* 138kHz - 1104kHz: Used for downstream transmission.

Note that the upstream frequency range is much smaller than the downstream frequency range. This is the asymmetric nature of ADSL; in true DSL, the upstream and downstream frequency spreads are equal. Also note that ADSL is a full duplex technology, which means that signals can be travelling in opposite directions at the same time, on a single wire. An easy way to conceptualize the use of the frequency ranges is to imagine the ranges as "pipes" through which the various signals travel like water. The larger the pipe, the more water can travel through it.

The two main frequency ranges are further subdivided into smaller units, called channels, each of which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the channels on the line to establish which ones have the best signal-to-noise ration, a measure of how much interference exists in that channel versus how strong the ADSL signal is. Interference on a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antennae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of available bandwidth decreases with each unusable channel.

 

==The Future of ADSL==

===The Growth of ADSL===
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of Highspeed Internet. Due to the ease of installation, and the fact that it utilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fibber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away, and a new one is installed less than 1km distant).

===New Devices===
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
Up until recently, when someone subscribed for ADSL service, they would receive an ADSL modem from the ISP. This modem would then be attached to the phone line and the subscriber's computer, providing Internet service. If the subscriber wished to use more than one computer with the service, he would be forced to purchase a router. Lately, ISPs have begun to distribute devices where are being termed "Home Gateways". These devices incorporate the ADSL modem, a 4 port home router, and a wireless access point into one compact form factor. With home networking on the rise, these devices are expected to be extremely popular with home users as they will limit the clutter required for a home network, and centralize control of all aspects of the network into one device.

===Competition===
Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the successor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widespread adoption in Japan and South Korea where it is the predominant high speed Internet technology.

 
==See Also==
[[Wireless Network Security]] 
[[WiMAX]] 
[[Mesh Networking]] 
[[Designing a Small Business Intranet]] 
[[Internet Cookies and Confidentiality]] 
 

==References==
# ADSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
# Tyson, Jeff. ''How VDSL Works''. How Stuff Works.com. Retrieved April 7, 2008 from [http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
# Volf, Zahy. Anita Demayo. Roei Limoni. ''ADSL''. RAD University. Retrieved April 7, 2008 from [http://www2.rad.com/networks/2005/adsl/main.htm]
# Hamill, Hugh et all. ''Asymmetric Digital Subscriber Line''. Retrieved April 7, 2008 from [http://www.esatclear.ie/~aodhoh/adsl/report.html]
# VDSL. (2008). ''Wikipedia'' Retrieved April 6, 2008 from [http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]
Bishop, Matt. Introduction to Computer Security. Boston: Addison-Wesley, 2006.

==External Links==
[http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 10:47, 9 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T01:57:06Z

Johnstfd: /* See Also */

ADSL (Asymmetric Digital Subscriber Line) is one of the leading technologies for providing high-speed Internet service to subscribers. ADSL is a variant of DSL, and there exists a common misconception that the A stands for Asynchronous. This is incorrect, as ADSL is a synchronous service. It is, however, asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

 
==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
===History===
Historically, Internet was served to people's homes through the use of voiceband data modems connect to the existing copper telephone line network. This network consists of twisted pair copper wires which run from a subscriber's home back to the telephone company's central office. The voiceband data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in harmony with a voice signal.

Traditionally, when ADSL was run to a home, a whole home splitter was installed at the demarcation point, the point where the phone line enters the home from the street. The splitter would filter all existing phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and install the device. Most ISPs have now adopted a much more passive stance wherein they ship the subscriber a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degradation of service for the consumer if they have more than 5 voiceband devices in their home. The reason for this is that the branching of the various phone lines causes reflections which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

===The Technology===
ADSL differs from standard DSL in that the data flow is asymmetric; data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are placed to Internet servers for websites or files, which are then downloaded to the subscriber's PC. Requests are much smaller than the files and websites they lead to, so there is little need for large upstream transmission capability. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, only recently has its bandwidth been fully used. The advent of technologies such as BitTorrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

 
==Functionality==
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
===Physical Setup===
The physical setup of the ADSL system is fairly symmetrical. The core of the setup is the DSLAM (Digital Subscriber Link Access Multiplexer), a device which is responsible for intermixing the voice and data signals on the downstream side of the connection, and for separating out the voice from the data signal on the upstream side.
On the upstream side, once the voice signal has been removed from the line, it is passed on to the phone company's telephony network. The data signal is passed onto the ISP's Internet backbone.
On the downstream side, the DSLAM combines the voice and data signals coming from the phone network and the Internet, and transmits them down the twister pair copper line to the subscriber's home. There is a physical distance restriction imposed here, of about 5km. This is the maximum distance that a signal from a DSLAM can travel without degradation. Beyond this point, Internet service may be intermittent, or slow, or just not possible. For this reason, ISPs will not provide ADSL to people living outside of the 5km service area of a DSLAM.
After the signal arrives at the subscriber's home, one of two situations is possible. Either a whole home splitter is installed, which filters the ADSL signal from the home's phone lines, and passes it along an unfiltered line to an ADSL modem, or the subscriber has installed microfilters on their voiceband devices, filtering out the ADSL at the wall jacks. Either way, the signal must now pass into an ADSL high speed modem, which will interpret the signal, and communicate with either a computer, or a router, providing Internet access. ADSL modems are power hungry devices and require their own power source; there is no way to incorporate them into a home computer system the way that voiceband modems have been.

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. The frequencies within the copper line are broken down as follows:
* 0kHz - 4kHz: Voiceband Services
* 4kHz - 28.875kHz: Unused buffer area
* 28.875kHz - 138kHz: Used for upstream transmission,
* 138kHz - 1104kHz: Used for downstream transmission.

Note that the upstream frequency range is much smaller than the downstream frequency range. This is the asymmetric nature of ADSL; in true DSL, the upstream and downstream frequency spreads are equal. Also note that ADSL is a full duplex technology, which means that signals can be travelling in opposite directions at the same time, on a single wire. An easy way to conceptualize the use of the frequency ranges is to imagine the ranges as "pipes" through which the various signals travel like water. The larger the pipe, the more water can travel through it.

The two main frequency ranges are further subdivided into smaller units, called channels, each of which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the channels on the line to establish which ones have the best signal-to-noise ration, a measure of how much interference exists in that channel versus how strong the ADSL signal is. Interference on a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antennae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of available bandwidth decreases with each unusable channel.

 

==The Future of ADSL==

===The Growth of ADSL===
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of Highspeed Internet. Due to the ease of installation, and the fact that it utilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fibber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away, and a new one is installed less than 1km distant).

===New Devices===
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
Up until recently, when someone subscribed for ADSL service, they would receive an ADSL modem from the ISP. This modem would then be attached to the phone line and the subscriber's computer, providing Internet service. If the subscriber wished to use more than one computer with the service, he would be forced to purchase a router. Lately, ISPs have begun to distribute devices where are being termed "Home Gateways". These devices incorporate the ADSL modem, a 4 port home router, and a wireless access point into one compact form factor. With home networking on the rise, these devices are expected to be extremely popular with home users as they will limit the clutter required for a home network, and centralize control of all aspects of the network into one device.

===Competition===
Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the successor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widespread adoption in Japan and South Korea where it is the predominant high speed Internet technology.

 
==See Also==
[[Wireless Network Security]] 
[[WiMAX]] 
[[Mesh Networking]] 
[[Designing a Small Business Intranet]] 
[[Internet Cookies and Confidentiality]] 
 

==References==
#[http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
#[http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
#[http://electronics.howstuffworks.com/vdsl3.htm http://electronics.howstuffworks.com/vdsl3.htm]
#[http://www2.rad.com/networks/2005/adsl/main.htm http://www2.rad.com/networks/2005/adsl/main.htm]
#[http://www.esatclear.ie/~aodhoh/adsl/report.html http://www.esatclear.ie/~aodhoh/adsl/report.html]
#[http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

 

==External Links==
[http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 10:47, 9 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T01:55:42Z

Johnstfd: /* See Also */

ADSL (Asymmetric Digital Subscriber Line) is one of the leading technologies for providing high-speed Internet service to subscribers. ADSL is a variant of DSL, and there exists a common misconception that the A stands for Asynchronous. This is incorrect, as ADSL is a synchronous service. It is, however, asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

 
==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
===History===
Historically, Internet was served to people's homes through the use of voiceband data modems connect to the existing copper telephone line network. This network consists of twisted pair copper wires which run from a subscriber's home back to the telephone company's central office. The voiceband data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in harmony with a voice signal.

Traditionally, when ADSL was run to a home, a whole home splitter was installed at the demarcation point, the point where the phone line enters the home from the street. The splitter would filter all existing phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and install the device. Most ISPs have now adopted a much more passive stance wherein they ship the subscriber a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degradation of service for the consumer if they have more than 5 voiceband devices in their home. The reason for this is that the branching of the various phone lines causes reflections which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

===The Technology===
ADSL differs from standard DSL in that the data flow is asymmetric; data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are placed to Internet servers for websites or files, which are then downloaded to the subscriber's PC. Requests are much smaller than the files and websites they lead to, so there is little need for large upstream transmission capability. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, only recently has its bandwidth been fully used. The advent of technologies such as BitTorrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

 
==Functionality==
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
===Physical Setup===
The physical setup of the ADSL system is fairly symmetrical. The core of the setup is the DSLAM (Digital Subscriber Link Access Multiplexer), a device which is responsible for intermixing the voice and data signals on the downstream side of the connection, and for separating out the voice from the data signal on the upstream side.
On the upstream side, once the voice signal has been removed from the line, it is passed on to the phone company's telephony network. The data signal is passed onto the ISP's Internet backbone.
On the downstream side, the DSLAM combines the voice and data signals coming from the phone network and the Internet, and transmits them down the twister pair copper line to the subscriber's home. There is a physical distance restriction imposed here, of about 5km. This is the maximum distance that a signal from a DSLAM can travel without degradation. Beyond this point, Internet service may be intermittent, or slow, or just not possible. For this reason, ISPs will not provide ADSL to people living outside of the 5km service area of a DSLAM.
After the signal arrives at the subscriber's home, one of two situations is possible. Either a whole home splitter is installed, which filters the ADSL signal from the home's phone lines, and passes it along an unfiltered line to an ADSL modem, or the subscriber has installed microfilters on their voiceband devices, filtering out the ADSL at the wall jacks. Either way, the signal must now pass into an ADSL high speed modem, which will interpret the signal, and communicate with either a computer, or a router, providing Internet access. ADSL modems are power hungry devices and require their own power source; there is no way to incorporate them into a home computer system the way that voiceband modems have been.

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. The frequencies within the copper line are broken down as follows:
* 0kHz - 4kHz: Voiceband Services
* 4kHz - 28.875kHz: Unused buffer area
* 28.875kHz - 138kHz: Used for upstream transmission,
* 138kHz - 1104kHz: Used for downstream transmission.

Note that the upstream frequency range is much smaller than the downstream frequency range. This is the asymmetric nature of ADSL; in true DSL, the upstream and downstream frequency spreads are equal. Also note that ADSL is a full duplex technology, which means that signals can be travelling in opposite directions at the same time, on a single wire. An easy way to conceptualize the use of the frequency ranges is to imagine the ranges as "pipes" through which the various signals travel like water. The larger the pipe, the more water can travel through it.

The two main frequency ranges are further subdivided into smaller units, called channels, each of which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the channels on the line to establish which ones have the best signal-to-noise ration, a measure of how much interference exists in that channel versus how strong the ADSL signal is. Interference on a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antennae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of available bandwidth decreases with each unusable channel.

 

==The Future of ADSL==

===The Growth of ADSL===
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of Highspeed Internet. Due to the ease of installation, and the fact that it utilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fibber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away, and a new one is installed less than 1km distant).

===New Devices===
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
Up until recently, when someone subscribed for ADSL service, they would receive an ADSL modem from the ISP. This modem would then be attached to the phone line and the subscriber's computer, providing Internet service. If the subscriber wished to use more than one computer with the service, he would be forced to purchase a router. Lately, ISPs have begun to distribute devices where are being termed "Home Gateways". These devices incorporate the ADSL modem, a 4 port home router, and a wireless access point into one compact form factor. With home networking on the rise, these devices are expected to be extremely popular with home users as they will limit the clutter required for a home network, and centralize control of all aspects of the network into one device.

===Competition===
Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the successor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widespread adoption in Japan and South Korea where it is the predominant high speed Internet technology.

 
==See Also==
[http://www.cas.mcmaster.ca/wiki/index.php/Wireless_Network_Security Wireless Network Security]
[http://www.cas.mcmaster.ca/wiki/index.php/WiMAX WiMAX]
[http://www.cas.mcmaster.ca/wiki/index.php/Mesh_Networking Mesh Networking]
[http://www.cas.mcmaster.ca/wiki/index.php/Designing_a_Small_Business_Intranet Designing a Small Business Intranet]
 

==References==
#[http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
#[http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
#[http://electronics.howstuffworks.com/vdsl3.htm http://electronics.howstuffworks.com/vdsl3.htm]
#[http://www2.rad.com/networks/2005/adsl/main.htm http://www2.rad.com/networks/2005/adsl/main.htm]
#[http://www.esatclear.ie/~aodhoh/adsl/report.html http://www.esatclear.ie/~aodhoh/adsl/report.html]
#[http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

 

==External Links==
[http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 10:47, 9 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T01:27:40Z

Johnstfd:

ADSL (Asymmetric Digital Subscriber Line) is one of the leading technologies for providing high-speed Internet service to subscribers. ADSL is a variant of DSL, and there exists a common misconception that the A stands for Asynchronous. This is incorrect, as ADSL is a synchronous service. It is, however, asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

 
==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
===History===
Historically, Internet was served to people's homes through the use of voiceband data modems connect to the existing copper telephone line network. This network consists of twisted pair copper wires which run from a subscriber's home back to the telephone company's central office. The voiceband data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in harmony with a voice signal.

Traditionally, when ADSL was run to a home, a whole home splitter was installed at the demarcation point, the point where the phone line enters the home from the street. The splitter would filter all existing phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and install the device. Most ISPs have now adopted a much more passive stance wherein they ship the subscriber a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degradation of service for the consumer if they have more than 5 voiceband devices in their home. The reason for this is that the branching of the various phone lines causes reflections which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

===The Technology===
ADSL differs from standard DSL in that the data flow is asymmetric; data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are placed to Internet servers for websites or files, which are then downloaded to the subscriber's PC. Requests are much smaller than the files and websites they lead to, so there is little need for large upstream transmission capability. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, only recently has its bandwidth been fully used. The advent of technologies such as BitTorrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

 
==Functionality==
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
===Physical Setup===
The physical setup of the ADSL system is fairly symmetrical. The core of the setup is the DSLAM (Digital Subscriber Link Access Multiplexer), a device which is responsible for intermixing the voice and data signals on the downstream side of the connection, and for separating out the voice from the data signal on the upstream side.
On the upstream side, once the voice signal has been removed from the line, it is passed on to the phone company's telephony network. The data signal is passed onto the ISP's Internet backbone.
On the downstream side, the DSLAM combines the voice and data signals coming from the phone network and the Internet, and transmits them down the twister pair copper line to the subscriber's home. There is a physical distance restriction imposed here, of about 5km. This is the maximum distance that a signal from a DSLAM can travel without degradation. Beyond this point, Internet service may be intermittent, or slow, or just not possible. For this reason, ISPs will not provide ADSL to people living outside of the 5km service area of a DSLAM.
After the signal arrives at the subscriber's home, one of two situations is possible. Either a whole home splitter is installed, which filters the ADSL signal from the home's phone lines, and passes it along an unfiltered line to an ADSL modem, or the subscriber has installed microfilters on their voiceband devices, filtering out the ADSL at the wall jacks. Either way, the signal must now pass into an ADSL high speed modem, which will interpret the signal, and communicate with either a computer, or a router, providing Internet access. ADSL modems are power hungry devices and require their own power source; there is no way to incorporate them into a home computer system the way that voiceband modems have been.

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. The frequencies within the copper line are broken down as follows:
* 0kHz - 4kHz: Voiceband Services
* 4kHz - 28.875kHz: Unused buffer area
* 28.875kHz - 138kHz: Used for upstream transmission,
* 138kHz - 1104kHz: Used for downstream transmission.

Note that the upstream frequency range is much smaller than the downstream frequency range. This is the asymmetric nature of ADSL; in true DSL, the upstream and downstream frequency spreads are equal. Also note that ADSL is a full duplex technology, which means that signals can be travelling in opposite directions at the same time, on a single wire. An easy way to conceptualize the use of the frequency ranges is to imagine the ranges as "pipes" through which the various signals travel like water. The larger the pipe, the more water can travel through it.

The two main frequency ranges are further subdivided into smaller units, called channels, each of which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the channels on the line to establish which ones have the best signal-to-noise ration, a measure of how much interference exists in that channel versus how strong the ADSL signal is. Interference on a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antennae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of available bandwidth decreases with each unusable channel.

 

==The Future of ADSL==

===The Growth of ADSL===
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of Highspeed Internet. Due to the ease of installation, and the fact that it utilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fibber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away, and a new one is installed less than 1km distant).

===New Devices===
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
Up until recently, when someone subscribed for ADSL service, they would receive an ADSL modem from the ISP. This modem would then be attached to the phone line and the subscriber's computer, providing Internet service. If the subscriber wished to use more than one computer with the service, he would be forced to purchase a router. Lately, ISPs have begun to distribute devices where are being termed "Home Gateways". These devices incorporate the ADSL modem, a 4 port home router, and a wireless access point into one compact form factor. With home networking on the rise, these devices are expected to be extremely popular with home users as they will limit the clutter required for a home network, and centralize control of all aspects of the network into one device.

===Competition===
Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the successor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widespread adoption in Japan and South Korea where it is the predominant high speed Internet technology.

 
==See Also==

 
==References==
#[http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
#[http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
#[http://electronics.howstuffworks.com/vdsl3.htm http://electronics.howstuffworks.com/vdsl3.htm]
#[http://www2.rad.com/networks/2005/adsl/main.htm http://www2.rad.com/networks/2005/adsl/main.htm]
#[http://www.esatclear.ie/~aodhoh/adsl/report.html http://www.esatclear.ie/~aodhoh/adsl/report.html]
#[http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

 

==External Links==
[http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 10:47, 9 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T01:20:19Z

Johnstfd:

ADSL (Asymmetric Digital Subscriber Line) is one of the leading technologies for providing high-speed Internet service to subscribers. ADSL is a variant of DSL, and there exists a common misconception that the A stands for Asynchronous. This is incorrect, as ADSL is a synchronous service. It is, however, asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

 
==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
===History===
Historically Internet was served to people's homes through the use of voiceband data modems connect to the existing copper telephone line network. This network consists of twisted pair copper wires which run from a subscriber's home back to the telephone company's central office. The voiceband data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in harmony with a voice signal.

Traditionally, when ADSL was run to a home, a whole home splitter was installed at the demarcation point, the point where the phone line enters the home from the street. The splitter would filter all existing phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and install the device. Most ISPs have now adopted a much more passive stance wherein they ship the subscriber a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degradation of service for the consumer if they have more than 5 voiceband devices in their home. The reason for this is that the branching of the various phone lines causes reflections which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

===The Technology===
ADSL differs from standard DSL in that the data flow is asymmetric; data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are placed to Internet servers for websites or files, which are then downloaded to the subscriber's PC. Requests are much smaller than the files and websites they lead to, so there is little need for large upstream transmission capability. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, only recently has its bandwidth been fully used. The advent of technologies such as Bit Torrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

 
==Functionality==
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
===The Physical Setup===
The physical setup of the ADSL system is fairly symmetrical. The core of the setup is the DSLAM (Digital Subscriber Link Access Multiplexer), a device which is responsible for intermixing the voice and data signals on the downstream side of the connection, and for separating out the voice from the data signal on the upstream side.
On the upstream side, once the voice signal has been removed from the line, it is passed on to the phone company's telephony network. The data signal is passed onto the ISP's Internet backbone.
On the downstream side, the DSLAM combines the voice and data signals coming from the phone network and the Internet, and transmits them down the twister pair copper line to the subscriber's home. There is a physical distance restriction imposed here, of about 5km. This is the maximum distance that a signal from a DSLAM can travel without degradation. Beyond this point, Internet service may be intermittent, or slow, or just not possible. For this reason, ISPs will not provide ADSL to people living outside of the 5km service area of a DSLAM.
After the signal arrives at the subscriber's home, one of two situations is possible. Either a whole home splitter is installed, which filters the ADSL signal from the home's phone lines, and passes it along an unfiltered line to an ADSL modem, or the subscriber has installed microfilters on their voiceband devices, filtering out the ADSL at the wall jacks. Either way, the signal must now pass into an ADSL high speed modem, which will interpret the signal, and communicate with either a computer, or a router, providing Internet access. ADSL modems are power hungry devices and require their own power source; there is no way to incorporate them into a home computer system the way that voiceband modems have been.

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. The frequencies within the copper line are broken down as follows:
* 0kHz - 4kHz: Voiceband Services
* 4kHz - 28.875kHz: Unused buffer area
* 28.875kHz - 138kHz: Used for upstream transmission,
* 138kHz - 1104kHz: Used for downstream transmission.

Note that the upstream frequency range is much smaller than the downstream frequency range. This is the asymmetric nature of ADSL; in true DSL, the upstream and downstream frequency spreads are equal. Also note that ADSL is a full duplex technology, which means that signals can be travelling in opposite directions at the same time, on a single wire. An easy way to conceptualize the use of the frequency ranges is to imagine the ranges as "pipes" through which the various signals travel like water. The larger the pipe, the more water can travel through it.

The two main frequency ranges are further subdivided into smaller units, called channels, each of which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the channels on the line to establish which ones have the best signal-to-noise ration, a measure of how much interference exists in that channel versus how strong the ADSL signal is. Interference on a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antennae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of available bandwidth decreases with each unusable channel.

 

==The Future of ADSL==

===The Growth of ADSL===
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of Highspeed Internet. Due to the ease of installation, and the fact that it utilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fibber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away, and a new one is installed less than 1km distant).

===New Devices===
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
Up until recently, when someone subscribed for ADSL service, they would receive an ADSL modem from the ISP. This modem would then be attached to the phone line and the subscriber's computer, providing Internet service. If the subscriber wished to use more than one computer with the service, he would be forced to purchase a router. Lately, ISPs have begun to distribute devices where are being termed "Home Gateways". These devices incorporate the ADSL modem, a 4 port home router, and a wireless access point into one compact form factor. With home networking on the rise, these devices are expected to be extremely popular with home users as they will limit the clutter required for a home network, and centralize control of all aspects of the network into one device.

===Competition===
Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the successor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widespread adoption in Japan and South Korea where it is the predominant high speed Internet technology.

 
==See Also==

 
==References==
#[http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
#[http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
#[http://electronics.howstuffworks.com/vdsl3.htm http://electronics.howstuffworks.com/vdsl3.htm]
#[http://www2.rad.com/networks/2005/adsl/main.htm http://www2.rad.com/networks/2005/adsl/main.htm]
#[http://www.esatclear.ie/~aodhoh/adsl/report.html http://www.esatclear.ie/~aodhoh/adsl/report.html]
#[http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

 

==External Links==
[http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 10:47, 9 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T01:14:23Z

Johnstfd:

ADSL (Asymmetric Digital Subscriber Line) is one of the leading technologies for providing high-speed Internet service to subscribers. ADSL is a variant of DSL, and there exists a common misconception that the A stands for Asynchronous. This is incorrect, as ADSL is a synchronous service. It is, however, asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

 
==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
===History===
Historically Internet was served to people's homes through the use of voiceband data modems connect to the existing copper telephone line network. This network consists of twisted pair copper wires which run from a subscriber's home back to the telephone company's central office. The voiceband data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in harmony with a voice signal.

Traditionally, when ADSL was run to a home, a whole home splitter was installed at the demarcation point, the point where the phone line enters the home from the street. The splitter would filter all existing phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and install the device. Most ISPs have now adopted a much more passive stance wherein they ship the subscriber a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degradation of service for the consumer if they have more than 5 voiceband devices in their home. The reason for this is that the branching of the various phone lines causes reflections which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

===The Technology===
ADSL differs from standard DSL in that the data flow is asymmetric; data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are placed to Internet servers for websites or files, which are then downloaded to the subscriber's PC. Requests are much smaller than the files and websites they lead to, so there is little need for large upstream transmission capability. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, only recently has its bandwidth been fully used. The advent of technologies such as Bit Torrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

 
==Functionality==
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
===The Physical Setup===
The physical setup of the ADSL system is fairly symmetrical. The core of the setup is the DSLAM (Digital Subscriber Link Access Multiplexer), a device which is responsible for intermixing the voice and data signals on the downstream side of the connection, and for separating out the voice from the data signal on the upstream side.
On the upstream side, once the voice signal has been removed from the line, it is passed on to the phone company's telephony network. The data signal is passed onto the ISP's Internet backbone.
On the downstream side, the DSLAM combines the voice and data signals coming from the phone network and the Internet, and transmits them down the twister pair copper line to the subscriber's home. There is a physical distance restriction imposed here, of about 5km. This is the maximum distance that a signal from a DSLAM can travel without degradation. Beyond this point, Internet service may be intermittent, or slow, or just not possible. For this reason, ISPs will not provide ADSL to people living outside of the 5km service area of a DSLAM.
After the signal arrives at the subscriber's home, one of two situations is possible. Either a whole home splitter is installed, which filters the ADSL signal from the home's phone lines, and passes it along an unfiltered line to an ADSL modem, or the subscriber has installed microfilters on their voiceband devices, filtering out the ADSL at the wall jacks. Either way, the signal must now pass into an ADSL high speed modem, which will interpret the signal, and communicate with either a computer, or a router, providing Internet access. ADSL modems are power hungry devices and require their own power source; there is no way to incorporate them into a home computer system the way that voiceband modems have been.

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. The frequencies within the copper line are broken down as follows:
* 0kHz - 4kHz: Voiceband Services
* 4kHz - 28.875kHz: Unused buffer area
* 28.875kHz - 138kHz: Used for upstream transmission,
* 138kHz - 1104kHz: Used for downstream transmission.

Note that the upstream frequency range is much smaller than the downstream frequency range. This is the asymmetric nature of ADSL; in true DSL, the upstream and downstream frequency spreads are equal. Also note that ADSL is a full duplex technology, which means that signals can be travelling in opposite directions at the same time, on a single wire. An easy way to conceptualize the use of the frequency ranges is to imagine the ranges as "pipes" through which the various signals travel like water. The larger the pipe, the more water can travel through it.

The two main frequency ranges are further subdivided into smaller units, called channels, each of which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the channels on the line to establish which ones have the best signal-to-noise ration, a measure of how much interference exists in that channel versus how strong the ADSL signal is. Interference on a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antennae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of available bandwidth decreases with each unusable channel.

 

==The Future of ADSL==
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of Highspeed Internet. Due to the ease of installation, and the fact that it utilizes technology already present in every home with a telephone, ADSL has become extremely popular.
*****MENTION GATEWAYS VS MODEMS*****
In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fibber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away, and a new one is installed less than 1km distant).

Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the successor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widespread adoption in Japan and South Korea where it is the predominant high speed Internet technology.
 
==See Also==

 
==References==
#[http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
#[http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
#[http://electronics.howstuffworks.com/vdsl3.htm http://electronics.howstuffworks.com/vdsl3.htm]
#[http://www2.rad.com/networks/2005/adsl/main.htm http://www2.rad.com/networks/2005/adsl/main.htm]
#[http://www.esatclear.ie/~aodhoh/adsl/report.html http://www.esatclear.ie/~aodhoh/adsl/report.html]
#[http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

 

==External Links==
[http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 10:47, 9 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T01:07:32Z

Johnstfd:

ADSL (Asymmetric Digital Subscriber Line) is one of the leading technologies for providing high-speed Internet service to subscribers. ADSL is a variant of DSL, and there exists a common misconception that the A stands for Asynchronous. This is incorrect, as ADSL is a syncronous servies. It is, however, asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

 
==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
===History===
Historically Internet was served to people's homes through the use of voiceband data modems connect to the existing copper telephone line network. This network consists of twisted pair copper wires which run from a subscriber's home back to the telephone company's central office. The voiceband data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in harmony with a voice signal.

Traditionally, when ADSL was run to a home, a whole home splitter was installed at the demarcation point, the point where the phone line enters the home from the street. The splitter would filter all existing phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and install the device. Most ISPs have now adopted a much more passive stance wherein they ship the subscriber a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degradation of service for the consumer if they have more than 5 voiceband devices in their home. The reason for this is that the branching of the various phone lines causes reflections which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

===The Technology===
ADSL differs from standard DSL in that the data flow is asymmetric; data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are placed to Internet servers for websites or files, which are then downloaded to the subscriber's PC. Requests are much smaller than the files and websites they lead to, so there is little need for large upstream transmission capability. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, only recently has its bandwidth been fully used. The advent of technologies such as Bit Torrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

 
==Functionality==
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
===The Physical Setup===
The physical setup of the ADSL system is fairly symetrical. The core of the setup is the DSLAM (Digital Subscriber Link Access Multiplexer), a device which is responsible for intermixing the voice and data signals on the downstream side of the connection, and for seperating out the voice from the data signal on the upstream side.
On the upstream side, once the voice signal has been removed from the line, it is passed on to the phone company's telephony network. The data signal is passed onto the ISP's Internet backbone.
On the downstream side, the DSLAM combines the voice and data signals coming from the phone network and the Internet, and transmits them down the twister pair copper line to the subscriber's home. There is a physical distance restriction impossed here, of about 5km. This is the maximum distance that a signal from a DSLAM can travel without degredation. Beyond this point, internet service may be intermittent, or slow, or just not possible. For this reason, ISPs will not provide ADSL to people living outside of the 5km service area of a DSLAM.
After the signal arrives at the subscriber's home, one of two situations is possible. Either a whole home splitter is installed, which filters the ADSL signal from the home's phone lines, and passes it along an unfiltered line to an ADSL modem, or the subscriber has installed microfilters on their voiceband devices, filtering out the ADSL at the wall jacks. Either way, the signal must now pass into an ADSL Highspeed modem, which will interpret the signal, and communicate with either a computer, or a router, providing Internet access. ADSL modems are power hungry devices and require their own power source; there is no way to incorporate them into a home computer system the way that voiceband modems have been.

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. The frequencies within the copper line are broken down as follows:
* 0kHz - 4kHz: Voiceband Services
* 4kHz - 28.875kHz: Unused buffer area
* 28.875kHz - 138kHz: Used for upstream transmission,
* 138kHz - 1104kHz: Used for downstream transmission.

ADSL is a full duplex technology, which means that signals can be traveling in opposite directions at the same time, on a single wire.

Each of the two frequency ranges is further subdivided into smaller units, called channels, which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the various channels on the line to establish which channels have the best signal-to-noise ration, a measure of how much interference exists in that channel versus how strong the ADSL signals are. Interference in a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antennae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of available bandwidth decreases with each unusable channel.

 

==The Future of ADSL==
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of Highspeed Internet. Due to the ease of installation, and the fact that it utilizes technology already present in every home with a telephone, ADSL has become extremely popular.
*****MENTION GATEWAYS VS MODEMS*****
In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fibber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away, and a new one is installed less than 1km distant).

Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the successor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widespread adoption in Japan and South Korea where it is the predominant Highspeed Internet technology.
 
==See Also==

 
==References==
#[http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
#[http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
#[http://electronics.howstuffworks.com/vdsl3.htm http://electronics.howstuffworks.com/vdsl3.htm]
#[http://www2.rad.com/networks/2005/adsl/main.htm http://www2.rad.com/networks/2005/adsl/main.htm]
#[http://www.esatclear.ie/~aodhoh/adsl/report.html http://www.esatclear.ie/~aodhoh/adsl/report.html]
#[http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

 

==External Links==
[http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 10:47, 9 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T01:01:03Z

Johnstfd:

ADSL (Asymmetric Digital Subscriber Line) is one of the leading technologies for providing high-speed Internet service to subscribers. ADSL is a variant of DSL, and there exists a common misconception that the A stands for Asynchronous. This is incorrect, as ADSL is a syncronous servies. It is, however, asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

 
==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
===History===
Historically Internet was served to people's homes through the use of voiceband data modems connect to the existing copper telephone line network. This network consists of twisted pair copper wires which run from a subscriber's home back to the telephone company's central office. The voiceband data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in harmony with a voice signal.

Traditionally, when ADSL was run to a home, a whole home splitter was installed at the demarcation point, the point where the phone line enters the home from the street. The splitter would filter all existing phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and install the device. Most ISPs have now adopted a much more passive stance wherein they ship the subscriber a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degradation of service for the consumer if they have more than 5 voiceband devices in their home. The reason for this is that the branching of the various phone lines causes reflections which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

===The Technology===
ADSL differs from standard DSL in that the data flow is asymmetric; data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are placed to Internet servers for websites or files, which are then downloaded to the subscriber's PC. Requests are much smaller than the files and websites they lead to, so there is little need for large upstream transmission capability. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, only recently has its bandwidth been fully used. The advent of technologies such as Bit Torrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

 
==Functionality==
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
===The Physical Setup===
The physical setup of the ADSL system is fairly symetrical. The core of the setup is the DSLAM (Digital Subscriber Link Access Multiplexer), a device which is responsible for intermixing the voice and data signals on the downstream side of the connection, and for seperating out the voice from the data signal on the upstream side.
On the upstream side, once the voice signal has been removed from the line, it is passed on to the phone company's telephony network. The data signal is passed onto the ISP's Internet backbone.
On the downstream side, the DSLAM combines the voice and data signals coming from the phone network and the Internet, and transmits them down the twister pair copper line to the subscriber's home. There is a physical distance restriction impossed here, of about 5km. This is the maximum distance that a signal from a DSLAM can travel without degredation. Beyond this point, internet service may be intermittent, or slow, or just not possible. For this reason, ISPs will not provide ADSL to people living outside of the 5km service area of a DSLAM.

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. There is an unused buffer area between 4kHz and 28.875kHz. The range from 28.875kHz to 138kHz is used for upstream transmission, while the region from 138kHz to 1104kHz is used for downstream. ADSL is a full duplex technology, which means that signals can be traveling in opposite directions at the same time, on a single wire.

Each of the two frequency ranges is further subdivided into smaller units, called channels, which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the various channels on the line to establish which channels have the best signal-to-noise ration, a measure of how much interference exists in that channel versus how strong the ADSL signals are. Interference in a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antennae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of available bandwidth decreases with each unusable channel.

 

==The Future of ADSL==
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of Highspeed Internet. Due to the ease of installation, and the fact that it utilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fibber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away, and a new one is installed less than 1km distant).

Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the successor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widespread adoption in Japan and South Korea where it is the predominant Highspeed Internet technology.
 
==See Also==

 
==References==
#[http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
#[http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
#[http://electronics.howstuffworks.com/vdsl3.htm http://electronics.howstuffworks.com/vdsl3.htm]
#[http://www2.rad.com/networks/2005/adsl/main.htm http://www2.rad.com/networks/2005/adsl/main.htm]
#[http://www.esatclear.ie/~aodhoh/adsl/report.html http://www.esatclear.ie/~aodhoh/adsl/report.html]
#[http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

 

==External Links==
[http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 10:47, 9 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T01:00:02Z

Johnstfd:

ADSL (Asymmetric Digital Subscriber Line) is one of the leading technologies for providing high-speed Internet service to subscribers. ADSL is a variant of DSL, and there exists a common misconception that the A stands for Asynchronous. This is incorrect, as ADSL is a syncronous servies. It is, however, asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

 
==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
===History===
Historically Internet was served to people's homes through the use of voiceband data modems connect to the existing copper telephone line network. This network consists of twisted pair copper wires which run from a subscriber's home back to the telephone company's central office. The voiceband data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in harmony with a voice signal.

Traditionally, when ADSL was run to a home, a whole home splitter was installed at the demarcation point, the point where the phone line enters the home from the street. The splitter would filter all existing phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and install the device. Most ISPs have now adopted a much more passive stance wherein they ship the subscriber a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degradation of service for the consumer if they have more than 5 voiceband devices in their home. The reason for this is that the branching of the various phone lines causes reflections which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

===The Technology===
ADSL differs from standard DSL in that the data flow is asymmetric; data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are placed to Internet servers for websites or files, which are then downloaded to the subscriber's PC. Requests are much smaller than the files and websites they lead to, so there is little need for large upstream transmission capability. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, only recently has its bandwidth been fully used. The advent of technologies such as Bit Torrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

 
==Functionality==
===The Physical Setup===
The physical setup of the ADSL system is fairly symetrical. The core of the setup is the DSLAM (Digital Subscriber Link Access Multiplexer), a device which is responsible for intermixing the voice and data signals on the downstream side of the connection, and for seperating out the voice from the data signal on the upstream side.
On the upstream side, once the voice signal has been removed from the line, it is passed on to the phone company's telephony network. The data signal is passed onto the ISP's Internet backbone.
On the downstream side, the DSLAM combines the voice and data signals coming from the phone network and the Internet, and transmits them down the twister pair copper line to the subscriber's home. There is a physical distance restriction impossed here, of about 5km. This is the maximum distance that a signal from a DSLAM can travel without degredation. Beyond this point, internet service may be intermittent, or slow, or just not possible. For this reason, ISPs will not provide ADSL to people living outside of the 5km service area of a DSLAM.
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. There is an unused buffer area between 4kHz and 28.875kHz. The range from 28.875kHz to 138kHz is used for upstream transmission, while the region from 138kHz to 1104kHz is used for downstream. ADSL is a full duplex technology, which means that signals can be traveling in opposite directions at the same time, on a single wire.

Each of the two frequency ranges is further subdivided into smaller units, called channels, which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the various channels on the line to establish which channels have the best signal-to-noise ration, a measure of how much interference exists in that channel versus how strong the ADSL signals are. Interference in a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antennae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of available bandwidth decreases with each unusable channel.

 

==The Future of ADSL==
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of Highspeed Internet. Due to the ease of installation, and the fact that it utilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fibber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away, and a new one is installed less than 1km distant).

Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the successor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widespread adoption in Japan and South Korea where it is the predominant Highspeed Internet technology.
 
==See Also==

 
==References==
#[http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
#[http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
#[http://electronics.howstuffworks.com/vdsl3.htm http://electronics.howstuffworks.com/vdsl3.htm]
#[http://www2.rad.com/networks/2005/adsl/main.htm http://www2.rad.com/networks/2005/adsl/main.htm]
#[http://www.esatclear.ie/~aodhoh/adsl/report.html http://www.esatclear.ie/~aodhoh/adsl/report.html]
#[http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

 

==External Links==
[http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 10:47, 9 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T00:27:03Z

Johnstfd:

ADSL (Asymmetric Digital Subscriber Line) is one of the leading methods of providing high-speed Internet service to subscribers. ADSL is a variant of DSL, with the A standing for Asymmetric, not Asynchronous as many people incorrectly believe it to be. The service is said to be asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

 
==Introduction to ADSL==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
Historically internet was served to people's homes through the use of voice frequency data modems connect to the existing copper telephone line network. This network consists of twister pair copper wires which run back to the telephone company's central office. The voice frequency data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in addition to a voice signal.
Traditionally when ADSL was run to a home, a whole home splitter was installed at the demarkation point (???), where the phone line comes in from the street to the home. The splitter would filter all exisiting phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and do the installation. Most ISPs have now adopted a much more passive stance where they ship the ADSL modem with a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degredation of service of the consumer if they have more than X telephonic devices in their home. The reason for this is that the branching of the various phone lines causes reflections, which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

 
==Functionality==
===The Physical Setup===
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
ADSL differs from standard DSL in that the data flow is asymmetric; the data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are made for websites or files, which are then downloaded from the Internet. The size of the site/file requests is small relative to the files and websites they are downloading. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, it has only recently begun to be used to its full bandwidth. The advent of technologies such as Bit Torrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

===Transmission===
Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. There is an unused buffer area between 4kHz and 28.875kHz. The range from 28.875kHz to 138kHz is used for upstream transmission, while the region from 138kHz to 1104kHz is used for downstream. ADSL is a full duplex technology, which means that signals can be traveling in opposite directions at the same time, on a single wire.

Each of the two frequency ranges is further sub-divded into smaller units, called channels, which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the various channels on the line to establish which channels have the best signal-to-noise ration, a messure of how much interference exists in that channel versus how strong the ADSL signals are. Interference in a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antenae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of avaialable bandwidth drecreases with each unusable channel.

 

==The Future of ADSL==
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of highspeed internet. Due to the ease of installation, and the fact that it unilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fiber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away,and a new one is installed less than 1km distant).

Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the sucessor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widesread adoption in Japan and South Korea where it is the predominant highspeed internet technology.
 
== '''See Also''' ==

 
==References==
#[http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
#[http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
#[http://electronics.howstuffworks.com/vdsl3.htm http://electronics.howstuffworks.com/vdsl3.htm]
#[http://www2.rad.com/networks/2005/adsl/main.htm http://www2.rad.com/networks/2005/adsl/main.htm]
#[http://www.esatclear.ie/~aodhoh/adsl/report.html http://www.esatclear.ie/~aodhoh/adsl/report.html]
#[http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

 

==External Links==
[http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 10:47, 9 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-14T00:24:13Z

Johnstfd: /* '''Functionality''' */

ADSL (Asymmetric Digital Subscriber Line) is one of the leading methods of providing high-speed Internet service to subscribers. ADSL is a variant of DSL, with the A standing for Asymmetric, not Asynchronous as many people incorrectly believe it to be. The service is said to be asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

 
== '''History''' ==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
Historically internet was served to people's homes through the use of voice frequency data modems connect to the existing copper telephone line network. This network consists of twister pair copper wires which run back to the telephone company's central office. The voice frequency data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in addition to a voice signal.
Traditionally when ADSL was run to a home, a whole home splitter was installed at the demarkation point (???), where the phone line comes in from the street to the home. The splitter would filter all exisiting phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and do the installation. Most ISPs have now adopted a much more passive stance where they ship the ADSL modem with a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degredation of service of the consumer if they have more than X telephonic devices in their home. The reason for this is that the branching of the various phone lines causes reflections, which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

 
== '''Functionality''' ==
{|align="right"
|-
| [[Image:ADSL_Physical.jpg|Frequency Usage in ADSL]]
|}
ADSL differs from standard DSL in that the data flow is asymmetric; the data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are made for websites or files, which are then downloaded from the Internet. The size of the site/file requests is small relative to the files and websites they are downloading. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, it has only recently begun to be used to its full bandwidth. The advent of technologies such as Bit Torrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. There is an unused buffer area between 4kHz and 28.875kHz. The range from 28.875kHz to 138kHz is used for upstream transmission, while the region from 138kHz to 1104kHz is used for downstream. ADSL is a full duplex technology, which means that signals can be traveling in opposite directions at the same time, on a single wire.

Each of the two frequency ranges is further sub-divded into smaller units, called channels, which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the various channels on the line to establish which channels have the best signal-to-noise ration, a messure of how much interference exists in that channel versus how strong the ADSL signals are. Interference in a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antenae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of avaialable bandwidth drecreases with each unusable channel.

 

== '''The Future of ADSL''' ==
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of highspeed internet. Due to the ease of installation, and the fact that it unilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fiber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away,and a new one is installed less than 1km distant).

Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the sucessor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widesread adoption in Japan and South Korea where it is the predominant highspeed internet technology.
 
== '''See Also''' ==

 
== '''References''' ==
#[http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
#[http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
#[http://electronics.howstuffworks.com/vdsl3.htm http://electronics.howstuffworks.com/vdsl3.htm]
#[http://www2.rad.com/networks/2005/adsl/main.htm http://www2.rad.com/networks/2005/adsl/main.htm]
#[http://www.esatclear.ie/~aodhoh/adsl/report.html http://www.esatclear.ie/~aodhoh/adsl/report.html]
#[http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

 

== '''External Links''' ==
[http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 10:47, 9 April 2008 (EDT)

File:ADSL Physical.jpg

2008-04-14T00:21:11Z

Johnstfd: The physical layout of a standard ADSL setup

The physical layout of a standard ADSL setup

Asymmetric Digital Subscriber Line

2008-04-13T22:24:10Z

Johnstfd:

ADSL (Asymmetric Digital Subscriber Line) is one of the leading methods of providing high-speed Internet service to subscribers. ADSL is a variant of DSL, with the A standing for Asymmetric, not Asynchronous as many people incorrectly believe it to be. The service is said to be asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

 
== '''History''' ==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
Historically internet was served to people's homes through the use of voice frequency data modems connect to the existing copper telephone line network. This network consists of twister pair copper wires which run back to the telephone company's central office. The voice frequency data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in addition to a voice signal.
Traditionally when ADSL was run to a home, a whole home splitter was installed at the demarkation point (???), where the phone line comes in from the street to the home. The splitter would filter all exisiting phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and do the installation. Most ISPs have now adopted a much more passive stance where they ship the ADSL modem with a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degredation of service of the consumer if they have more than X telephonic devices in their home. The reason for this is that the branching of the various phone lines causes reflections, which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

 
== '''Functionality''' ==
{|align="right"
|-
| [[Image:ADSL_Frequencies.jpg|thumb|Frequency Usage in ADSL]]
|}
ADSL differs from standard DSL in that the data flow is asymmetric; the data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are made for websites or files, which are then downloaded from the Internet. The size of the site/file requests is small relative to the files and websites they are downloading. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, it has only recently begun to be used to its full bandwidth. The advent of technologies such as Bit Torrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. There is an unused buffer area between 4kHz and 28.875kHz. The range from 28.875kHz to 138kHz is used for upstream transmission, while the region from 138kHz to 1104kHz is used for downstream. ADSL is a full duplex technology, which means that signals can be traveling in opposite directions at the same time, on a single wire.

Each of the two frequency ranges is further sub-divded into smaller units, called channels, which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the various channels on the line to establish which channels have the best signal-to-noise ration, a messure of how much interference exists in that channel versus how strong the ADSL signals are. Interference in a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antenae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of avaialable bandwidth drecreases with each unusable channel.

 
== '''The Future of ADSL''' ==
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}
In recent years ADSL has enjoyed a huge surge in popularity. As the Internet grows and the demand for streaming video and other such high bandwidth applications increases, voiceband technology has been all but abandoned in favour of highspeed internet. Due to the ease of installation, and the fact that it unilizes technology already present in every home with a telephone, ADSL has become extremely popular.

In the coming years, ADSL service providers will continue to expand their coverage. As things stand at the moment, ADSL is only available in densely populated areas, and even then there are gaps in the service. This stems from the fact that the ADSL signal degrades rapidly and becomes unstable at distances great than 5km. Service providers are solving this problem by running fiber optic lines from the central office to remote DSLAMs in locations where service was previously unavailable. The practice can also increase the speeds available to people who already fall within an ADSL service area by connecting them to a DSLAM which is closer to their home (for instance if they were previously being served from a DSLAM 4.5km away,and a new one is installed less than 1km distant).

Despite its recently surge, however, when one looks to the future of ADSL over the next ten years, the outlook does not look good. New technologies are emerging that could eclipse and even replace ADSL altogether. Some ISPs have already begun to roll out the sucessor to ADSL, ADSL2, which features greater bandwidth and speeds through the use of greater frequency ranges. However, even the new ADSL2 is eclipsed by the emerging VDSL (also known as VHDSL). VDSL, Very High Speed Digital Subscriber Line, provides speeds up to 100Mbits/s in both directions through the utilization of frequencies up to 30MHz. Though it is still an emerging technology in the Western world, VDSL has seen widesread adoption in Japan and South Korea where it is the predominant highspeed internet technology.
 
== '''See Also''' ==

 
== '''References''' ==
#[http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
#[http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
#[http://electronics.howstuffworks.com/vdsl3.htm http://electronics.howstuffworks.com/vdsl3.htm]
#[http://www2.rad.com/networks/2005/adsl/main.htm http://www2.rad.com/networks/2005/adsl/main.htm]
#[http://www.esatclear.ie/~aodhoh/adsl/report.html http://www.esatclear.ie/~aodhoh/adsl/report.html]
#[http://en.wikipedia.org/wiki/VDSL http://en.wikipedia.org/wiki/VDSL]

 

== '''External Links''' ==
[http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 10:47, 9 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-13T21:59:57Z

Johnstfd:

ADSL (Asymmetric Digital Subscriber Line) is one of the leading methods of providing high-speed Internet service to subscribers. ADSL is a variant of DSL, with the A standing for Asymmetric, not Asynchronous as many people incorrectly believe it to be. The service is said to be asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competitive force in the Internet service market.

ADSL provides much greater bandwidth than traditional voiceband modems, but does so while utilizing the same copper phone lines.

__TOC__

 
== '''History''' ==
{|align="right"
|-
| [[Image:Microfilter.jpg|thumb|A standard ADSL Microfilter]]
|-
| [[Image:ADSL_Modem.jpg|thumb|A standard ADSL Highspeed Modem]]
|}
Historically internet was served to people's homes through the use of voice frequency data modems connect to the existing copper telephone line network. This network consists of twister pair copper wires which run back to the telephone company's central office. The voice frequency data modem made use of the same frequencies as human speech, up to about 3.4kHz, and as such was only able to achieve speeds of up to 56Kbps. This also had the disadvantage of tying up the phone line whenever the modem was in use. ADSL makes use of other frequencies which are not needed by traditional telephony services, allowing an ADSL signal to exist on a copper line in addition to a voice signal.
Traditionally when ADSL was run to a home, a whole home splitter was installed at the demarkation point (???), where the phone line comes in from the street to the home. The splitter would filter all exisiting phone lines in the home, and provide an unfiltered line for use by the ADSL modem. This approached proved to be rather expensive for the ISP as they would have to cover the cost of the splitter, as well as the technician who would go out and do the installation. Most ISPs have now adopted a much more passive stance where they ship the ADSL modem with a number of microfilters which users will have to place on each of their telephones. While cheaper for this ISP, this can lead to degredation of service of the consumer if they have more than X telephonic devices in their home. The reason for this is that the branching of the various phone lines causes reflections, which interfere with the ADSL signal. A whole home splitter solves this problem in that there are no reflections; the ADSL modem is connected directly to the splitter, and is alone on an unfiltered line.

 
== '''Functionality''' ==
{|align="right"
|-
| [[Image:ADSL_Frequencies.jpg|thumb|Frequency Usage in ADSL]]
|}
ADSL differs from standard DSL in that the data flow is asymmetric; the data flow is greater in one direction. This is due to the observation that most people use the Internet in a fairly passive fashion. Requests are made for websites or files, which are then downloaded from the Internet. The size of the site/file requests is small relative to the files and websites they are downloading. As the Internet grows, so too does the size of the files people are downloading, and the size of the websites they are visiting. It makes sense that users should have a greater ability to download and view these files. In fact, even though the upload pipeline is very small, it has only recently begun to be used to its full bandwidth. The advent of technologies such as Bit Torrent, which focuses on equal uploading and downloading, has finally begun to use the full upload bandwidth.

Traditional voice telephony only utilizes a very small portion of the possible bandwidth in a copper wire. In fact, all voiceband communications fall within the range between 0 and 4kHz. ADSL makes use of the higher frequencies supported by the copper wire. There is an unused buffer area between 4kHz and 28.875kHz. The range from 28.875kHz to 138kHz is used for upstream transmission, while the region from 138kHz to 1104kHz is used for downstream. ADSL is a full duplex technology, which means that signals can be traveling in opposite directions at the same time, on a single wire.

Each of the two frequency ranges is further sub-divded into smaller units, called channels, which span approximately 4kHz. When an ADSL link is first established the modem on the user end and the DSLAM on the provider end test the various channels on the line to establish which channels have the best signal-to-noise ration, a messure of how much interference exists in that channel versus how strong the ADSL signals are. Interference in a channel can come from poor wire quality, noise on the line, or even AM radio signals (a copper phone line can be thought of as a large antenae). Once the best channels are determined, these channels are used for communication. If the signal ever becomes degraded to the point that communication is no longer possible, the channels are re-evaluated. It should be noted, however, that the amount of avaialable bandwidth drecreases with each unusable channel.

 
== '''The Future of ADSL''' ==
{|align="right"
|-
| [[Image:ADSL_Gateway.jpg|thumb|A modern ADSL Gateway]]
|}

 
== '''See Also''' ==

 
== '''References''' ==
#[http://http://en.wikipedia.org/wiki/Adsl http://http://en.wikipedia.org/wiki/Adsl]
#[http://electronics.howstuffworks.com/vdsl1.htm http://electronics.howstuffworks.com/vdsl1.htm]
#[http://electronics.howstuffworks.com/vdsl3.htm http://electronics.howstuffworks.com/vdsl3.htm]
#[http://www2.rad.com/networks/2005/adsl/main.htm http://www2.rad.com/networks/2005/adsl/main.htm]
#[http://www.esatclear.ie/~aodhoh/adsl/report.html http://www.esatclear.ie/~aodhoh/adsl/report.html]

 

== '''External Links''' ==
[http://http://www.speedtest.net/ Internet Speed Test]

----

--[[User:Johnstfd|Durandal]] 10:47, 9 April 2008 (EDT)

Asymmetric Digital Subscriber Line

2008-04-13T18:31:39Z

Johnstfd: /* '''References''' */

Asymmetric Digital Subscriber Line

2008-04-13T18:21:14Z

Johnstfd:

Asymmetric Digital Subscriber Line

2008-04-13T18:20:21Z

Johnstfd:

Asymmetric Digital Subscriber Line

2008-04-13T18:19:30Z

Johnstfd:

Asymmetric Digital Subscriber Line

2008-04-13T17:17:27Z

Johnstfd:

File:ADSL Frequencies.jpg

2008-04-13T17:17:17Z

Johnstfd: A breakdown of the frequencies used in ADSL

A breakdown of the frequencies used in ADSL

Asymmetric Digital Subscriber Line

2008-04-13T16:45:37Z

Johnstfd:

Asymmetric Digital Subscriber Line

2008-04-13T16:44:49Z

Johnstfd:

Asymmetric Digital Subscriber Line

2008-04-13T16:44:01Z

Johnstfd: /* '''The Future of ADSL''' */

Asymmetric Digital Subscriber Line

2008-04-13T16:43:18Z

Johnstfd: /* '''History''' */

File:ADSL Modem.jpg

2008-04-13T16:41:31Z

Johnstfd: A standard ADSL modem.

A standard ADSL modem.

File:ADSL Gateway.jpg

2008-04-13T16:41:10Z

Johnstfd: A modern ADSL gateway, combining ADSL Modem, 4 port router, and wireless router.

A modern ADSL gateway, combining ADSL Modem, 4 port router, and wireless router.

File:Microfilter.jpg

2008-04-13T16:40:32Z

Johnstfd: A standard ADSL Microfilter.

A standard ADSL Microfilter.

Asymmetric Digital Subscriber Line

2008-04-13T03:48:00Z

Johnstfd:

Asymmetric Digital Subscriber Line

2008-04-13T03:36:04Z

Johnstfd: /* '''History''' */

Asymmetric Digital Subscriber Line

2008-04-13T03:22:43Z

Johnstfd:

Asymmetric Digital Subscriber Line

2008-04-13T03:12:17Z

Johnstfd:

Asymmetric Digital Subscriber Line

2008-04-13T03:10:44Z

Johnstfd:

ADSL

2008-04-13T03:09:23Z

Johnstfd: Redirecting to Asymmetric Digital Subscriber Line

#REDIRECT [[Asymmetric_Digital_Subscriber_Line]]

ADSL

2008-04-13T03:09:11Z

Johnstfd: Redirecting to Asymmetric Digital Subscriber Line?redirect=yes

#REDIRECT [[Asymmetric_Digital_Subscriber_Line?redirect=yes]]

ADSL

2008-04-13T03:07:10Z

Johnstfd: Redirecting to Asymmetric Digital Subscriber Line

#REDIRECT [[Asymmetric_Digital_Subscriber_Line]]

Asymmetric Digital Subscriber Line

2008-04-09T14:59:14Z

Johnstfd:

Asymmetric Digital Subscriber Line

2008-04-09T14:48:42Z

Johnstfd: /* Asymmetric Digital Subscriber Line */

Asymmetric Digital Subscriber Line

2008-04-09T14:47:37Z

Johnstfd: New page: == Asymmetric Digital Subscriber Line == ADSL (Asymmetric Digital Subscriber Line) is one of the leading methods of providing high-speed Internet service to subscribers. ADSL is a varia...

== Asymmetric Digital Subscriber Line ==

ADSL (Asymmetric Digital Subscriber Line) is one of the leading methods of providing high-speed Internet service to subscribers. ADSL is a variant of DSL, with the A standing for Asymmetric, not Asynchronous as many people incorrectly believe it to be. The service is said to be asymmetric because the available upstream bandwidth is much less than the downstream bandwidth. Though there are some limitations imposed on the technology such as maximum bandwidth, and maximum distance from the Central Office, ADSL continues to be a competative force in the Internet service market.

----

--[[User:Johnstfd|Durandal]] 10:47, 9 April 2008 (EDT)

ADSL

2008-03-26T02:39:10Z

Johnstfd: New page: Temporary Page.

Temporary Page.