Switch Function

So you have to decide whether or not to use switches or hubs in you network? Well first we need to understand what a collision domain is. A collision domain is one or more devices sharing the same bandwidth. To better understand this think about it like this. One car on a freeway will have no trouble, but when you add more and more cars to the freeway the traffic flow continues to slow down. It is the same way with bandwidth. Hubs will not create there own freeway, they will use another already existing one. A switch on the other hand will create there own freeway. They will create there own collision domain. Thus the traffic will flow faster.

Address Learning: When a switch is turned on for the first time its MAC filtering table is empty. When a frame arrives for the first time the table records where the source address is from. Then the switch floods the network with the frame because it doesn’t know the destination address. When it arrives at the destination address it sends back the address to the switch. It is then logged into the table. From this point forward the table has a point-to-point connection. The result is that each frame will only be forwarded between the two devices.

Forward Decisions: When a frame arrives at a switch its addresses is compared in the MAC table. If the destination address is listed then it is only sent out to that address. The switch does not transmit the frame to any other areas of the network. This is called frame/filtering, it saves bandwidth on the network by not sending frames to unnecessary places on the network.

Loop Avoidance: When there are multiple connections between switches loops can occur on the network. Loops are when a frame goes around and around on the network, decreasing your bandwidth. To stop network loops the STP (Spanning Tree Protocol) is used.