TELECOM Digest OnLine - Sorted: Phone Line on cat 5 10-Base-T Ethernet?

Phone Line on cat 5 10-Base-T Ethernet?
9 May 2005 08:55:21 -0700

I'm a little bit new to the actual specifications of hardware
operations so this is something I wanted to ask because it seems to be
the case according to what I've read. (I've been primarily a software
person myself.)

I understand that standard 4-pair wire (cat 5) running data at 10mbps
does not use the blue/white and blue pair (wires 4 and 5), which is
typically the standard color for running a phone line along an
ethernet wire.

If this is correct, is it possible to run a standard analog phone line
over cat 5 ethernet sold in hardware or computer stores, simply by
connecting to the blue & blue/white pair and using that? Since the
wire is typically twisted pairs, I had the impression this was
possible without crosstalk between either the ethernet and the phone

Also, if the network cards being used are of the typical 10/100 type
that sell these days for $20 or less, or are included on the
motherboard of the user's PC, does that mean you can't do this because
100mbps will use all 4 pairs, or is it that you can run 100mbps
service over the other pairs and it won't really use the inner
blue-blue/white pair?

The things I have read indicate there are two types of 100mbps
service, 100Base-T, 100Base-T4 and 100Base-T8, where 100base-T8 uses
all of the wires in a 4-pair ethernet cable, and 100-Base-T4 uses only
two of the pairs. How would I know which is being used in ordinary

This also seems to imply that the other pair (wires 7 & 8) is also
available for use as phone service, conceivably implying you can run
100mbps ethernet and two analog phone lines on the same 4-pair cable
without problems or interference. I'd like to know if this is the

Paul Robinson

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