Collision Domains

[Lillyput]

Hi ,
In the first chapter of internetworkng , you have mentioned that each port of a switch is one collision domain say , if we have a four port switch with four host connected to each port , there will be no collision of data among them .

Agreed but what does a switch exactly do to break these collision domain . It is a layer 2 switch , which reads MAC addresses but then what makes it have collision domains equal to no of ports it have .

Todd m not able a get a clear picture , please explain !!!!!

[Fuzz]

With a hub, all devices are connected to each other inside the hub. Each port you connect up adds another device sharing the bandwidth. A switch does not connect devices together until it needs to send a received frame out an exit port. Only then does the frame get switched to the correct port, and only that port. So you see, the data from all devices connected to the switch never reach a central point, they just get sent to where they need to go (unless it is a broadcast frame of course). If two devices both wanted to reach the same destination, switches can use store-and-forward to hold the frame until the destination is clear and the frame can then be sent.

It's not what the switch does once it receives a frame that provides seperate collision domains, it's the fact that it resides at the data-link layer, as opposed to hubs at the physical layer.

[lildeezul]

A switches hardware, and fabric is very much different than the hubs... Thats was provides the collision domains... its hardware..

Also remeber hubs have no idea of addresses, there dump and just foward/amplify the data off all ports.

with switches, they keep a table called the CAM/MAC-address table, which is built off of source mac address, therefore switches can send data destined to a device off the port on which it resides, except if the table is not populated (dont contain the MAC) or if a broadcast (stated by fuzz)...
Switches are smarter devices.......WAY SMARTER

[Lillyput]

Thanks a tonne 4 the reply.

[Lillyput]

Hey thanks . made things more clear now