Logical Topologies

Logical topologies have the same names as physical topologies. But a physical topology describe the network, whereas the logical topology describes the network from the viewpoint of the data traveling on the network. Networks can have different physical and logical topologies.

The following two logical topologies are discussed in the following sections:

• Ring Logical topology
• Bus logical topology

1. Ring Logical Topology

Ring topology functions by passing data transmission from one node to the next. This operation is clearest when the physical topology is also a ring. Any time data are passed from node-to-node, the network has a ring logical topology.

Another way to identify a ring is to determine whether each node has separate receive and transmit circuits. If that is the case, the node is functioning as a repeater and is probably connected in a logical ring network.

2. Bus Logical Topology

In a bus topology, each data transmission passes by each node on the network. Essentially, each transmission is broadcast throughout the network and the nodes use addresses to determine whether they should pay attention. Any time all transmissions are available to all nodes on the network, the network has a bus logical topology.

If the nodes on a network use the same circuits to transmit and receive, the logical network is a bus.

Considerations when choosing a topology:

1. Money: A linear bus network may be the least expensive way to install a network; Need not to purchase concentrators.
2. Length of cable needed: The linear bus network uses shorter lengths of cable.
3. Future growth: With a star topology, expanding a network is easily done by adding another concentrators.
4. Cable type: The most common cable in schools is unshielded twisted pair, which is most often used with star topologies.