Ethernet: The Definitive Guide

Chapter 18. Ethernet Switching Hubs

Ethernet switching hubs allow you to build large Ethernet systems that extend beyond the limits of a single collision domain. They also link Ethernet segments that operate at different speeds and control the flow of traffic through a system. Switching hubs improve the reliability of Ethernet systems, and can vastly increase the amount of Ethernet bandwidth available for use. In recent years, the cost of switching hubs has plummeted while the performance and set of features has increased. As a result, Ethernet switching hubs are widely used today.

The operation of a switching hub is based on Ethernet bridging. Bridges are packet switches that operate at the level of Ethernet frames. The earliest Ethernet bridges were two-port devices that could link two Ethernet segments together. Later, it became possible to design and sell bridges with many ports, which were used in the hub of a cabling system, which is how they came to be known as a switching hub. In this chapter we use the word “bridge” and “switch” interchangeably when describing how these devices function.

This chapter describes how switching hubs function, and how they can be used to extend the reach and capability of an Ethernet system. The use of switching hubs in network designs is a big topic, and one that cannot be fully explained here. Instead, we provide a basic introduction to the technology and a quick look at the many features of switching hubs. This makes it possible for you ...