bluegene,
The term "collision domain" is a bit of a holdover from the days when we connected to hubs and all the computers shared the same collision domain, being divided into collision domains by switches and broadcast domains by routers.
With the price of switches no longer a factor - our connection point for most networks is a layer 2 switch instead of the layer 1 hub. Cost would no longer be a factor - you could not even find "new" hubs if you wanted!
That time passed about 7-8 years ago when the price of switches dropped - you would have a hard time finding a hub other then in the used section on eBay.
You still might find some holdovers in some older networks but most hubs have found there way to eBay or the dumpster!
We still see the idea of a "collision domain" in wireless networks as nodes all compete to be on the same channel.
Hope this helps!
E.A. Broda
CCNA, CCDA, CCAI, Network +
