Ref: 05270024
Title: Isolating telephone-line problems; Hayes modems can be sensitve
Date: 12/22/86

Copyright 3Com Corporation, 1991.  All rights reserved.

I have been having all kinds of problems with 3+Route hanging up.
I have traced some of the problems to the fact that Hayes modems are
very sensitive to line quality problems.  If you have both modems
answering with the initial and answer back tones but failure to lock
on carrier, the modems will eventually time-out and disconnect.  You
will need to have the phone company come out and do a bit-error check
on the line.  In my case, I had a line with bad "carbons," which means
a poor contact somewhere along the path from my office to the central
office.  We had our line changed to a different trunk, and the problem
went away.

Here are some troubleshooting methods to help determine whether
or not there is a telephone line quality problem:

1. Set up a PC with a Hayes 2400 baud modem inside the same
facility and establish the link over the a local phone line to
another server. The lines should have very little amplitude or
phase distortion. Data will pass easily. (Surely the Hayes 2400
will be able to autoequalize over this low impairment line). If
the connection (answer modem connected to COM1) stays UP, then
the COM1 problem may be a line problem.

2.  Try making the call (originating inside the office) using a
Hayes 1200 modem (or configure the Hayes 2400 baud configured for
1200).  I believe the modem will exhibit better performance at
the slower baud rate. If the connection (answer modem connected
to COM1) stays UP then the COM1 problem may be a line problem.

This problem happened again after we moved.  This time the phone
repairman said we had a marginal line but acceptable for voice
traffic.  He suggested we rent a "data-only"  line, which could
be conditioned for modems.  The problem was the same; our modem
would answer incoming calls, but never transfer any data.  The
calling party would continue to redial, trying to complete the
call.  Our solution was to install a different modem on our end.
We installed a UDS (Motorola) 2400 Hayes-compatible, and the
problem went away again.   The UDS product is much more forgiving
of poor line conditions.

Another problem is an apparent failure on COM1 of a 3+ 1.1
3Server3, where the call is initiated from our office.  Data is
transmitted for a short time (30 secs), and the 3Server3
disconnects in the middle of the transmission.  This problem has
been fixed in 3+1.2.
