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From: ncpjmw@brahms.amd.com (Mike Wincn)
Newsgroups: comp.dcom.lans
Subject: Re: 10BaseT Wiring question
Summary: Co-resident 10Base-T should be feasible.
Message-ID: <1990Dec8.011255.29729@amd.com>
Date: 8 Dec 90 01:12:55 GMT
References: <677@nih-csl.nih.gov>
Sender: usenet@amd.com (NNTP Posting)
Organization: Advanced Micro Devices; Sunnyvale, CA
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In article <677@nih-csl.nih.gov> brunetti@dumbo.nih.gov (Jim Brunetti) writes:
>Can anyone tell me if the 10BaseT spec has any mention of having multiple
>data  runs in the same sheath.  We have run 4 pair to locations running Starlan
>and were wondering if we could use the 2 unused pair for another connection.
>Should we use separate cable runs for each connection?  Will there be
>crosstalk?  Also I need to know the model number of the cable that AT&T
>recommends for Starlan.  Thanks.
>                  Jim Brunetti brunetti@dumbo.dcrt.nih.gov

It should be possible to use 10Base-T in bundles up to 25 pairs of 24 AWG 
wire, with any number of combinations of other services used on the
other pairs without significant degradation of performance, either on 
the 10Base-T link or the other services.  The standard does stipulate
noise characteristics that a 10Base-T receiver is supposed to reject in 
favor of valid Manchester packets, and those characteristics are believed to
be representative of a worst-case network noise environment, whether or not
that noise arises from co-resident services, and this includes NEXT, FEXT,
impulse noise, ringer hits, and other sources. 

There is no document that I know of which can perfectly anticipate all 
imaginable network operating conditions, or all realizable noise sources,
and your particular network may or may not exceed conditions outlined in the
standard.  But insofar as various noise sources in your particular network
do not exceed that described in the standard, you should have no trouble 
establishing a viable co-resident 10Base-T link. 

Having said that, I have not yet seen any new data on 10Base-T in 25-pair 
bundles, so I cannot yet comment on the success of the work done in 
drafting 10Base-T, and "existence proof" is the final arbiter. 

Mike Wincn 	ncpjmw@brahms.AMD.COM 
(408) 749-3156  DISCLAIMER:  I speak for myself unless noted otherwise.