BROCADE IP PRIMER

Chapter 1: Networking BasicsHalf-duplex vs. Full-duplexEthernet uses two ways to communicate from one machine to the next. Let'slook at them both.Half-duplexRemember when we talked about the early days of Ethernet? It used a bustopology (several computers connected to one cable)? This worked okay, but itonly provided half-duplex communication. Half-duplex is the polite way to communicate.You don't speak while the other person is talking (in this case, youcan't). One device speaks at a time.Think of half-duplex as a train on a railroad track. The train can obviously onlymove in one direction, and there can't be any other trains on the track. If thereare, that could cause a collision.Half-duplexSendor Receiveor Collision!As we described earlier, when a collision occurs, both talkers stop talking, andwait for a random period of time before they try again. This is certainly a politeway to communicate, but it's not very efficient. But because the cable couldonly carry one signal, that's all the original Ethernet could do. One electricalsignal. One train. One track.Hubs run into a similar problem. These are incapable of anything other thanhalf-duplex communication as well. They simply repeat the signal, much likethe main cable of the bus topology (even though a hub would make it a startopology).A group of computers connected to a hub (or even several hubs) would be considereda collision domain. This defines an area in the network wherecollisions may occur. Just like two people trying to have a conversation in acrowded room, the more people in the room, the greater the possibility thattwo people will be trying to talk at the same time (collision). As you can imag-30 Brocade IP Primer