Here's an email I got from a friend who used to do installs for Metro
Communications:

============
You'll get throughput and crosstalk issues on a 100 pair backbone.  Thats
only good for phone systems, and is being phased out by cat5 anyway....
Here's what you can do....

Cat 5 has 4 pairs, the blue and white sets and the orange and white are used
for T568-B (99.9 percent of ethernet cabeling), full duplex.  So, you can
really get 2 ethernet connections out of every one 4 pair cable.  What I
would do is buy 50 ft of 6 pair bundled Cat 5 (they shrink-wrap 6 cables
into one), and terminate them on a 110 Cat 5 block.  That will give you 12
stations per trunk (or 24 if your half-duplex).  Then, run each cable from
that point to each room from the attic.

Just make sure to split the cable on the 110 block on both ends.

Actually, if you want, you can run 2 cat 3 lines as well, terminate them on
the block, and run data and PHONE on the same wires, and split them into 2
or 3 jacks at each drop.
==================

> -----Original Message-----
> From: Brian [mailto:lxy at cloudnet.com] 
> Sent: Monday, November 12, 2001 3:44 PM
> To: tclug-list at mn-linux.org
> Subject: Re: [TCLUG] Ethernet wall jacks
> 
> 
> On Mon, 12 Nov 2001, Petre Scheie wrote:
> 
> > The problem with a 100-pair cable is you'll get crosstalk between 
> > pairs.
> 
> Cat5 and Cat6 do not exist in multi-pair configurations.  
> Every rule of networking says you do not, under any 
> circumstances, run multi-pair for networking.  I believe the 
> best you can buy is Cat3 certified, which will technically 
> run 10 Mbit.  Just run 50 Cat6 runs.  You'll be better off in 
> the end by far.
> 
> -Brian
> 
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