Date: Sat, 12 Dec 92 16:45:00 -0600
From: bill.garfield@yob.sccsi.com (Bill Garfield)
Newsgroups: comp.dcom.telecom
Subject: Re: Wanted: Help With Multi-Tech/Courier Modem Problem
Reply-To: bill.garfield@yob.sccsi.com (Bill Garfield)
Organization: Ye Olde Bailey BBS - Houston, TX - 713-520-1569
X-Submissions-To: telecom@eecs.nwu.edu
X-Administrivia-To: telecom-request@eecs.nwu.edu
X-Telecom-Digest: Volume 12, Issue 901, Message 5 of 5

description of modem dialback problem deleted ...

> Is it possible that the local telephone lines are affecting the
> signal, whereas the long-distance has *some* difference that would
> account for the weird behavior?

Yes -- but good luck in attempting to prove it to the phone company.

I just SUCCESSFULLY solved a long-standing similar problem with a
local customer here in Houston (but two telco central offices away)
who, often as not, could *NOT* get a facsimile transmission to go
through from their office to mine. The failure rate was an alarming
60% on the average. We fought it for almost a year, different fax
machines, different extensions, same deal, only this ONE customer
could not fax to us, and the problem was only one direction.
Practically drove us cuckoo.

The problem turned out to be inter-machine trunk (IMT) trouble between
two of Bell's larger Houston central offices. (We suspected this was
the problem some months ago, but were in a quandry as to how to
convincingly pose our dilemma to the teledroids answering the phones
at Repair Service) ;)

My solution involved having the fellow at the other end "route" or
"call forward always" an extension on his PBX to an extension on my
pbx via the public-switched telephone network.  I then dialed the
"remote" telephone number which caused the phone on the other side of
my desk to ring. When I answered the call, it naturally passed VOICE
flawlessly.  I called it several more times, flawless voice every
call.  Finally, for grins, on one of the calls, I held down the 9 and
# buttons on 1 phone (1477hz) and LISTENED to the tone coming through
the other phone.  One direction the tone came through fine.  Going the
other way, the tone had suddenly acquired a pulsating
"bling-bling-bling-bling-bling" about 10db down from the tone and at
approx 2 ips.  I tried holding down the 1 and 2 buttons (697hz), and
the pulsations were still there, but now you had to really listen to
hear them.

Over on my mdf, I connected a Halcyon Transmission Test Set (tone
generator) to the outgoing line (set for -13dbm) and put my Sage 930A
D & I test set on the inbound T-1 span coming from Bell. With the
Halcyon generating standard 1004hz test tone, the pulsations were
barely noticeable.  These became very pronounced as the frequency was
raised above 1300hz. By the time I got up to 2000hz the
"bling-bling-bling" was _very_ distinct ... you couldn't miss it.

I called the PBX tech at the other end and had him listen in on his
incoming and outgoing trunks.  As expected, the tone passing through
his office was clear.  I next removed my tone generator and had the
pbx tech at the other end put his generator on the circuit toward me.
I was still getting the "bling-bling-bling" pulsations.  I had him
decrease his level by 20db, still "bling-bling-bling-bling".

I got Southwestern Bell's special services folks in on it and asked
them to trace the call through the various central offices, making
note of the fact that the "bling-bling-bling" wasn't there at the
originating end, and emphasizing that the whole purpose of the trace
was to try and determine at what point in the call's routing were the
pulsations being introduced.  I emphasized to them, "It is not an
errant call, please do not knock it down, just trace it cable and
pair, span and channel."

After some 4-1/2 hours and a visit to my office by a SWB Special
Services tech (after I escalated the problem up to a third level
supervisor), the problem suddenly cleared, just like magic.  "Came
clear while checking" was the response.  Horsefeathers!  Something
that has haunted us for the past 11 months doesn't magically go away.

Back on the phone to the third level supervisor, I was adamant that I
had to have a logical and plausible resolution report, and that "Came
clear while testing" wouldn't sit well upstairs with my people.

The following day I received a call from a first line supervisor
informing me that a Bell interoffice tech found and pulled down a
loopback off of an unused but "mated" T-1c (48 channel) system.  They
(Bell) had been taking "density errors" on an inter-office T-3 span
for a long time but had ignored the alarm condition as seemingly no
one had complained, and of course ordinary voice passed through just
fine.  (Mated systems cannot be placed in loopback because of clocking
problems, or so I'm told).

Well now, all of a sudden everyone's fax machine works just fine.
14.4k bps modems which had trouble staying linked at 2400 began
working at full speed and two local bbs' report remarkable
improvements in callers' ability to link with them.

FYI:  I coincidently happen to be a Multi-Tech field beta test site
      and the MT1432BA/A is, IMHO, one of the finest products they have
      ever built.  1.02A firmware is the current release & is stable.
      It uses an AT&T data pump.  I am unfamiliar with the Courier
      2400E.

Something else you might try.  On the Multi-Tech, disable v.42 error
checking in favor of plain vanilla MNP-4.  The Multi-Tech string to do
this is; AT&E1&E14#L1 and be sure to "store" it with AT&W0. This has
_frequently_ worked with some unfriendly USR's.


bill.garfield@yob.sccsi.com (Bill Garfield) | Standard disclaimer applies.
PBX/Datacom Specialist                      | Opinions are my own and not
Panhandle Eastern Corp                      | those of my employer. I speak
Voice: 713.627.5228                         | for no one.  I am not an
Data:  713.520.1569                         | employee nor representative
FAX:   713.627.5285                         | of Multi-Tech Systems, Inc.

Ye Olde Bailey BBS   Houston,Texas   Node 1: 1 713 520 1569  yob.sccsi.com