Most implementations of Ethernet over CAT5 use two of the four pairs leaving two 'free'. Not quite sure what you're asking - are you looking for a way to have two Ethernet connections running on a single CAT5 cable? You can do this; and you can even buy splitter units to do the job, and it will probably work but it won't comply with the CAT5 standards. I'd be careful about employing such a technique in a commercial network
