Path: utzoo!attcan!uunet!europa.asd.contel.com!seka.scc.com!enger
From: enger@seka.scc.com (Robert M. Enger)
Newsgroups: comp.dcom.modems
Subject: Re: Line Noise Redux
Keywords: Line Noise
Message-ID: <1991Jan13.183631.27081@europa.asd.contel.com>
Date: 13 Jan 91 23:36:30 GMT
References: <59420@aurs01.UUCP> <1991Jan10.042007.4227@ims.alaska.edu> <59426@aurs01.UUCP> <1991Jan13.113822.13888@chinet.chi.il.us>
Reply-To: enger@seka.scc.com
Organization: CONTEL Federal Systems
Lines: 28
Nntp-Posting-Host: seka.scc.com


SLIC-96 is indeed a "carrier" based, pair-gain system.
If you are using a SLIC-96, then you are NOT copper all the way to the CO.
(slic stands for something like Subscriber Line Interface Concentrator).
The SLIC-96 hubs upto 96 subscriber lines into a central point
(usually a controlled environment vault, CEV).  From there, 4 T1 circuits
convey the info back to the CO.  It is possible that real T1's are not
evn used.  Often, the T1's are themselves further multiplexed together
and placed on a Fiber span.

At any rate, all of this means that you are indeed in "4-wire" mode
between your premesis and the CO.  So, you may have problems wiht
the interface card in the SLIC, etc.


SECOND point.  From what I've read of the problem, the situation
is asymmetric:  Outside callers dialing INTO your modem see the problem.

The following experiment might provide an interesting data point:
find a willing outside caller that REPEATABLY gets the problem when dialing
into your modem.  Then, try initiating an OUTGOING  call from your 
troublesome modem TO the outside caller.  This will reverse the usage
of the low/high frequencies.  If the problem reverses, then maybe it
is a frequency dependent line degredation of some sort.

Best wishes,
Bob Enger
enger@seka.scc.com