Newsgroups: comp.dcom.telecom.tech,alt.dcom.telecom,comp.dcom.cabling,comp.dcom.lans.misc
Subject: Re: 10base-T & POTS in same Cat-5 cable?
References: <[email protected]>
DaveC  writes:

> Is it acceptable to use 1 pair in a Cat-5 cable for POTS when 2 pair are 
> being used for 10base-T? Wondering about cross-talk, etc., introducing noise 
> between these two.

The UTP Ethernet "standard" before 10Base-T was called StarLan 
and it was specifically designed to have telephone signals and 
1 Mbit/s Ethernet on the same cable terminated to RJ-45 connectors. 

The 10Base-T system was an officially standardized faster version 
of this. In the design of 10Base-T it was designed so that the 
signal can travel trough the telephone wires, and can travel 
through the same cables that carry also telephone signals. 
10Base-T and PSTN telephone on the same CAT5 cable works. 

This kind of arrangement might not be up to the newest cabling 
recommendations / standards, but it works. 
In modern system it is a pain in the neck to wire two different 
signals to one connector at both ends since all the termination
equipment (typically RJ-45 jacks) is designed generally with one 
jack-one cable paradigm in mind. I think that modern standards say 
that you are not supposed to share horizontal cable between 
applications. But sharing osa same cable will work with 10Base-T. 

The is not much crosstalk between different pairs on CAT5 wiring 
and 10Base-T is very robust system (with sitable filters it is 
possible to even run 10Base-T signals and normal telephone signals 
on the same wire pair, there are products that do this). 
Sharing the cable between telephone and some faster Ethernet standard 
might be more problematic, because those tend to be more sensitive 
to the noise and some implementations use more wire pairs. 
100Base-TX when run with telephone might still work but there 
coudl be reaiabity problems. You can't run 1000Base-T with any 
other signals, because gigabit Ethernet on copper use all 
of the four wire pairs in CAT5 wire.




-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/