 cable must meet these values at 100m. It is one thing to say, "Propagation delay skew shall not exceed 45 ns/100m." It is quite another to say, "The cable must not exceed 100m." Semantics aside, keeping your Cat-5e cable lengths within 100m is a good idea. Segments are divided by repeaters or hubs. Figure 2-1 shows a repeater extending the distance between a server and a personal computer. A hub is like a repeater, except that while a repeater may have only two connectors, a hub can have many more; that is, it repeats a signal over many cables as opposed to just one. Figure 2-2 shows a hub connecting several computers to a network. In Ethernet network design, repeaters and hubs are treated the same way. The 5-4-3 rule of Ethernet design states that between any two nodes on an Ethernet network, there can be only five segments, connected via four repeaters, and only three of the segments can be populated. This rule, which seems odd in the context of today's net- works, was the source of much pain for those who didn't understand it. Repeater Figure 2-1. Repeater extending a single 10Base-T link Figure 2-2. Hub connecting multiple hosts to a network Chapter 2: Hubs and Switches As hubs became less expensive, extra hubs were often used as repeaters in more com- plex networks. Figure 2-3 shows an example of how two remote groups of users could be connected using hubs on each end and a repeater in the middle. Hubs are very simple devices. Any signal received on any port is repeated out every other port. Hubs are purely physical and electrical devices, and do not have a presence on the network (except possibly for management purposes). They do not alter frames or make decisions based on them in any way. Figure 2-4 illustrates how hubs operate. As you might imagine, this model can become problematic in larger networks. The traffic can become SO intensive that the network becomes saturated-it someone prints a large file, everyone on the network will suffer while the file is transferred to the printer over the network. If 