Ref: 13390007
Title: Troubleshooting a Multiconnect Environment
Date: 1/29/90

Copyright 3Com Corporation, 1991.  All rights reserved.

In a Multiconnect environment, most problems are caused by illegal
and incorrectly configured networks.  Some problems may be caused by
older versions of Multiconnect hardware, although only in very
large network configurations.  To identify the problem and a solution
as quickly as possible, follow these steps.

1. Verify that the network configuration meets IEEE 802.3
requirements.

2. Identify the problem clearly.  Can users log on to the server?
Is the network response very slow?  Does the network function
sporadically?

If you experience any of the above symptoms on your network, use
a LAN monitor on the network to determine what sort of errors are
exhibited.

3. Check to see if any of the following solutions will help.

   Problem                     Possible Cause and Solution
   -------       ---------------------------
   Cannot log on to server     Cabling may be faulty or netserver
               may be crashing.  Test cabling and
               server to identify the problem.

   Slow network response       Double termination of the BNC module.
          The BNC module is shipped internally
                               terminated (jumper at position JP2).
       Therefore, if the BNC module needs to
       be externally terminated, move the
       jumper from JP2 to JP1 and make sure a
       terminator is installed at the Multi-
       Connect end of the segment and at the
                               far end of the segment.

   Sporadic network operation  Illegal cable lengths (exceeding
               IEEE 802.3 specs) or more than four
       repeaters in a row.  File transfers
             that halt with a timeout are good
       indicators that the segment length
       is too long.

   Modules behave abnormally   Improper grounding.  Each segment
   or inconsistently       should be grounded to building
       ground at one point only, anywhere
       along the segment.  For convenience,
       a grounding screw is provided on the
       module to ground the segment at the
       repeater.

4. Check to see if your MultiConnect modules are current:

                       Previous             Current
   Controller           3787-02 Rev A        3787-02 Rev E
   BNC                  3796-01 Rev D        3796-04 Rev F
   DIX                  3793-01 Rev C        3793-05 Rev E

The fatherboard, regardless of the revision level, should not
exhibit any problems.  Only small changes were made to the original
product, such as a resistor change to correct theoretical values.
The controller board was changed to correct jitter problems that
caused slow network response.

All phases of the Multiconnect modules are compatible with each
other; old controllers can be used with new modules and vice
versa.

All Multiconnect modules can be used as per the user guides with
the following exception:  Phase 2 Transceiver Interface Modules
(Assy number 3793-03) cannot be connected to transceivers that
have the SQE function enabled, including the 3Com 5.0 transceiver
(the long gray one).  The 3C108 has a jumper to select SQE; make
certain it is not selected.  Although the IEEE prohibits use of SQE
with repeaters, we have provided that option (with Phase 1 and 3
TIMs) as a feature.

5.  Contact your network supplier to request current versions
of the Multiconnect module.  The upgrades should resolve any
problems you may have after the network has been verified to be
configured correctly.

