LAN and WAN Topologies 1

Topology refers to how network equipment is arranged in order to communicate. How this is
done could be limited by the communication protocols the equipment uses, cost, geography, or
other factors, such as the need for redundancy should the main link fail.
You should also note that there is often a difference between physical and logical topology.
Physical topology is how the network appears when you look at it, whereas logical topology is
how the network sees itself. The most common topologies are described in the following
sections.

Point-to-Point

This topology is used mainly for WAN links. A point-to-point link is simply one in which one
device has one connection to another device. You could add a secondary link connecting each
device but if the device itself fails, then you lose all connectivity.

 

 

Bus

This topology was created with the first Ethernet networks, where all devices had to be
connected to a thick cable referred to as the backbone. If the backbone cable fails, then the
network goes down. If a cable linking the device to the backbone cable fails, then only that
device will lose connection.
Figure 

 

Star

This is probably the most common topology you will encounter. Each network device is
connected to a central hub or switch. If one of the cables to the devices fails, then only that
device becomes disconnected. 

 

Figure 1.6 – Star Topology

Ring

A ring topology is used by token ring networks and Fiber Distributed Data Interface (FDDI)
networks, both of which went out of use several years ago. 

 

Figure 1.7 – Token Ring Topology 

A ring topology that is used with FDDI networks employs a dual-ring connection to provide
redundancy should one ring fail.

 

Figure 1.8 – Dual-Ring Topology