Ethernet Topology

Ethernet Topology

Ethernet is defined at the data link layer of the OSI model and uses what is commonly referred to as a bus topology. A bus topology consists of devices strung together in series with each device connecting to a long cable or bus. Many devices can tap into the bus and begin communication with all other devices on that cable segment. This means that all the network devices are attached to a single wire and are all peers, sharing the same media.

Bus topology has two very glaring faults. First, if there were a break in the main cable, the entire network would go down. Second, it was hard to troubleshoot. It took time to find out where the cable was cut off. The star topology has been deployed for a long time now and is the standard in the LAN environment. Star topologies link nodes directly to a central point. The central point is either a hub or a LAN switch. Ethernet hubs are multiport repeaters, meaning they repeat the signal out each port except the source port.

The advantages of a physical star topology network are reliability and serviceability. If a point-to-point segment has a break, in the star topology, it will affect only the node on that link. Other nodes on the network continue to operate as if that connection were nonexistent. Ethernet hubs and LAN switches act as the repeaters that centralize the twisted-pair media. Twisted-pair media can also be used to join like devices. Following the OSI model and the concept of interchangeable parts, even Token Ring, which is a logical ring, can use a physical star topology with twisted pair.