Giuseppe Larosa Thu, 01/29/2009 - 00:58
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Hello Louie,


all devices connected to an hub are in competition for bandwidth usage:

MAC layer needs to listen to wire to see if the bus is free for use to listen to its own frame to detect possible collisions.

In case of collision the frames needs to be retramsmitted (up to 16 times with a random exponential backoff (waiting) timer at each attempt).

Instead with a switch:

if you connect a PC NIC directly to the switch port the NIC doesn't need to wait for the wire to be free and a true full duplex communication is possible.


The switch backplane is capable to move multiple frames at the same time between its ports.

So each switch port is a separated collision domain that provides dedicated bandwidth to the user (10+10, 100+100, or 1000+1000 Mbps) on each port.


In addition the ports can be placed in different groups = L2 broadcast domains to provide other advantages by avoiding to propagate broadcast frames to all ports.


Now, the price per port of switches is so low that is becoming difficult to find hubs.


Advantages are clear


Hope to help

Giuseppe

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