Network Topology

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Revision as of 23:31, 12 April 2009

Network topology refers to the configuration of the physical and logical connections between the elements (links, nodes, etc.) of a network. Network topology does not refer to the physical layout of a network, nor does it refer to transmission rates, signal types or other characteristics of computer networks. Networks are normally organized by one (or more) of five basic types of topologies: bus, ring, star, tree, and mesh. In some instances two networks are interconnected forming a sixth type of topology: hybrid.

Types of Network Topology

Bus

The bus topology uses a single transmission medium on which all messages are broadcasted. Each node receives all messages, but only the intended destination accepts it. Only one message can be sent at a time.

Advantages

• Requires a minimal amount of connections.
• Simple to configure.

Disadvantages

• A fault in the main connection can bring down the entire network.
• Very unsafe. Each computer receives all messages on the network. A computer can still accept messages even if its address does not match the destination address.
• Is slow, and prone to collision problems.

Ring

In a ring topology each node is connected to exactly two other nodes forming a closed loop. Messages are passed along the ring in a single direction until they reach their destination.

Advantages

Disadvantages

Star

The star topology consists of a hub, router, etc., connecting each other node of the network. Each message passes through the hub and is redirected to its destination.

Advantages

• Easy to detect errors and faults. Each node is separate from all other nodes through the hub, so it is easy to isolate and fix the problem.
• Any break in a connection between the hub and a node will not cause a failure in the network.
• Minimizes the number of possible collisions.

Disadvantages

• If the hub has a fault, the entire network can fail.

Tree

Combining the characteristics of multiple star networks along a single bus network with a root node forms the tree topology. The hub/central node of each star network is connected to the root node of the tree creating multiple tiers on the network. The root node of the tree connects with the central node of the star network, which connects to more nodes in lower tiers.

Advantages

• Easy to expand.
• Allows for much larger number of nodes than bus or star networks individually, without having the same speed and size limitations.
• If there is a fault in the root node, the connections within each of the second tier networks will not be lost.

Disadvantages

• If there is a fault in the root node, the connection between each of the second tier networks can be lost.
• Is more complex some other topologies, making it more difficult to configure.

Mesh

Mesh topologies present multiple paths that a message can take to reach their destination. Each node is connected to one or more other nodes. If each node is connected to every other nodes then it is called fully connected or a full mesh. Messages are passed along the network by using a routing algorithm or table which determines the next nodes the message will take to reach its destination.

Advantages

• Creates inherent failure protection through the redundancy of connections between nodes. There is generally multiple paths from one node to another, so a network fault will generally not cause a node from being disconnected from the network.
• May be easy to expand. Only a small number of nodes may need to have their routing algorithms/tables updates to expand the network.

Disadvantages

• Can be much more complex than other topologies. As the size of a mesh network grows the number of connections can grow exponentially, with the most extreme growth rate occurring in full meshes.
• If the routing algorithm/table is not properly implemented on any number of nodes a number of errors can occur, such as lost messages or messages continuously passing through a cycle.
• May be very difficult to expand. As highlighted in a full mesh, all nodes will need to have their routing algorithms/tables updates to include the new nodes.

Centralization

Decentralization