Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!tektronix!reed!omen!percival!bucket!martyl
From: martyl@bucket.UUCP (Marty Lee)
Newsgroups: comp.dcom.modems
Subject: Re: Twisted Pair Ethernet
Message-ID: <600@bucket.UUCP>
Date: Thu, 26-Nov-87 12:32:10 EST
Article-I.D.: bucket.600
Posted: Thu Nov 26 12:32:10 1987
Date-Received: Sun, 29-Nov-87 18:09:03 EST
References: <2247@kitty.UUCP> <2250@kitty.UUCP>
Organization: Rick's Home-Grown UNIX; Portland, OR.
Lines: 42
Summary: Use of T1 carrier

In article <2250@kitty.UUCP>, larry@kitty.UUCP (Larry Lippman) writes:
> In article <[STL-HOST1.ARPA]Fri,.20.Nov.87.07:29:01.CST.SNELSON>, SNELSON@STL-HOST1.ARPA writes:
> > LETS NOT MIX UP BITS AND HERTZ. ON IN HOUSE T-1 WE MAKE SURE THAT
> > THE SEND AND RECEIVE ARE IN SEPARATE CABLE BUNDLES. THEY DON'T
> > CROSS TALK TO EACH OTHER THAT WAY.
> 
> 	There is special outside telephone cable available for T1 use
> which divides cable pairs into two major bundles, using a Z-shaped
> shield which makes contact with the outer alpeth shield.  Such an
> arrangement allows separation of transmit and receive directions.
> 	However, much of the existing T1 carrier goes through conventional
> telephone cables comprising only one overall alpeth shield.  Some attempt
> is made to keep transmit and receive pairs in different 25-pair binder
> groups, though.
> 	Crosstalk is not that much of a problem with T1 systems as long as:
> (1) the outside cable is in decent shape and moisture-free; and (2) the
> outside regenerators are installed at recommended locations.
> 

As far as the transmit and receive pairs are concerned there are only three
types of separations, same binder group, adjacent binder groups and non-adjacentbinder groups.
If the transmit and receive binder groups are separated by atleast one
spare binder group then it is the same as T-screened cable or two cables.
The density of carrier systems is not as good as a T-screened cable but cheaper
most of the time and an existing cable may be converted.  The binder(s)
used between the tx and rx may then be used for low speed data and VF, so
all is not lost.

Now if you go to T1C (48 channels) then the whole ball game changes and all
bets are off.  T1C is much more sensitive to crosstalk and induced noise.

Disclaimer: Good T1 designs are a must for any network.  Take your time and
don't rush into it, mistakes can be costly and will shape your network
for the coming years.  I work for a RBOC but they don't have to do all
the work.  (The Dept. of Justice may have something to say about this subject.)





-- 
tektronix!reed!omen!bucket!martyl  (Marty Lee)