Global Systems for Mobile Communications (GSM)
From Computing and Software Wiki
Global System for Mobile Communication (GSM) is the worldwide standard for mobile phones. It is estimated that 80% of the world market uses this standard for mobile communication. GSM has the unique advantage of allowing customers to roam from network to network without switching phones. Furthermore, it gives networks the advantage of choosing from many vendors who implement GSM. Moreover, GSM pioneered two key mobile inventions known as the Subscriber Identity Module (SIM), and the short message service ( SMS). Finally, GSM also created a worldwide standard emergency number 112, to allow travelers to connect to an emergency line without knowing the local number.
Contents |
History
In Europe, in was quickly realized the disadvantage of each European country operating on their exclusive network. This prevented cell phones from being carried over from country to country. Obviously this was seen as a problem with the frequent travel between countries in Europe. Consequently, the Conference of European Posts and Telegraphs (CEPT) assembled a research group called Group Spécial Mobile (GSM). Later on the acronym GSM had been changed to Global Systems Mobile Communications.
Technical Information
GSM Network
GSM is a cellular network. This means that phones connect to it by searching for something called a cell. In the GSM network there are five different types of cells that differ based on size: macrocells, microcell, picocells, femtocells, and umbrella cells. The macrocell is implemented in such a way that the base station antenna is installed above average roof top level. Furthermore, microcells have their antenna installed at a height that is usually lower than then average roof top level. Thirdly, picocells are small cells whose coverage is only a few dozen meters, and are mainly used for indoors. Fourthly, femtocells connect to a service provider network via a broadband internet connection and are typically used for residential or small business environments. Finally, umbrella cells are used to fill in the gaps of coverage between small cells. Cell coverage varies depending on the antenna height, gain, and propagation conditions. Practically, the longest a cell can cover is 35 kilometers. Moreover, excellent indoor coverage can be achieved by using an indoor picocell base station. In addition, an indoor repeater with distributed indoor antennas can be fed through power splitters, and transmit signals from outdoor antennas through to the indoor distributed attenna system.
Network Structure
The network behind the GSM is broken into three basic sections:
- The Base Station Subsystem
- The Network and Switching Subsystem
- The GPRS Core Network which allows packet based internet connections.
Subscriber Identity Module (SIM)
One of the main services that GSM provides is the Subscriber Identity Module (SIM card). The SIM card is essentially a small smart card that is inserted into the user’s handset and contains their subscriber information and phonebook. The beauty of this card is that it allows users to move their mobile subscription and phonebook to another phone by simply inserting the card into a new GSM phone. Some network providers will block this by forcing the user to use a phone and/or SIM card issued by them. This technique is know as SIM locking and is illegal in some countries.
GSM Frequencies
GSM networks operate in two main frequency ranges, namely GSM frequency range for 2G, and UTMS frequency bands for 3G. 2G GSM in most countries operates in at frequency rate of 900 MHZ or 1800 MHz. However, some networks in the United States and Canada operate at the 850MHz or 1900 Mhz bands since the 900Mhz and 1800MHz may already be used. 3G GSM networks in Europe typically operate in the 2100 MHz frequency band, and 1900 MHz in North America.
GSM Security
GSM Security is comprised of subscriber identity authentication, subscriber identity confidentiality, signaling data confidentiality, and user data confidentiality. A subscriber is uniquely identified by their International Mobile Subscriber Identity (IMSI). This information is deemed as sensitive and in the design of GSM authentication scheme, this information is never transmitted over radio. Moreover, a challenge-response scheme is used to perform authentication. Conversations are encrypted using a temporary randomly generated cipher key. The GSM handset identifies itself by means of a Temporary Mobile Subscriber Identity (TMSI). The TMSI is issued by the network and may be changed while the device is not in use.
Three different elements make up the security mechanism of GSM: the SIM card, the GSM handset or Mobile Station (MS), and the actual GSM network. The SIM card contains the IMSI and the subscriber authentication Key (K), an authentication algorithm (A3), a ciphering key generating algorithm (A8) and a Personal Identification Number (PIN). Another algorithm (A5) is located in the actual GSM handset. In addition, the three encryption algorithms (A3, A5, A8) are also located in the GSM network. Inside a part of the GSM network known as the the authentication center (AUC) a database consists of IMSI, the TMSI, and subscriber authentication key for each user.
References
- Margrave, David. "GSM Security and Encryption", George Manson University
- GSM on Wikipedia
- The History of GSM Technology
- GSM World Home
See Also
External Links
--Mankarn 22:26, 12 April 2009 (EDT)
