Network segment

A network segment is a portion of a computer network. The nature and extent of a segment depends on the nature of the network and the device or devices used to interconnect end stations.

Ethernet

Electrically connected segment

According to the defining IEEE standards for Ethernet, a network segment is an electrical connection between networked devices using a shared medium.

In the original 10BASE5 and 10BASE2 Ethernet varieties, a segment would therefore correspond to a single coax cable and any devices tapped into it. At this point in the evolution of Ethernet, multiple network segments could be connected with repeaters (in accordance with the 5-4-3 rule for 10 Mbit Ethernet) to form a larger collision domain.

Layer 1 segment

With twisted-pair Ethernet, electrical segments can be joined together using repeaters or repeating hubs. This corresponds to the extent of a OSI Layer 1 network and is equivalent to the collision domain.

Layer 2 segment

Using switches or bridges, multiple layer 1 segments can be combined to a common layer 2 segment, i.e. all nodes can communicate with each other through MAC addressing or broadcasts. A layer 2 segment is equivalent to the broadcast domain.