Ref: 04450003
Title: Some ELMC-TP Adapter Tranceivers May Have Problems in Max-Length Runs
date:  8/20/91

Copyright 3Com Corporation, 1991.  All rights reserved.


Some EtherLink Microchannel Twisted Pair (ELMC-TP) adapters may experience
poor performance on Receive when installed on wire segments that are near
the maximum specified length.  This problem does not occur on EtherLink
II-TP.  ELMC-TP at rev B resolves the problem.

The problem was first noticed on a Synoptics Lattisnet network (prior to
10Base-T Specs) using ELMC-TP adapters Revs E to G.  Problems have not been
seen on recent Rev A-level adapters but it is thought that any MC-TP adapter
prior to Rev B potentially could experience Receive problems on some
maximum-length wiring runs.

Note:  Many adapters never will experience the problem due to random tolerance
spreads on chip timings, so it is important to ensure that adapters have the
problem before replacing them.  Wholesale swapping of adapters is not
indicated.

Symptoms of the problem are random errors (that is, network retries) in
normal operation, or failure of the Echo Test of the MC diagnostics.  The
following methods may help to verify that network problems are not from
some other cause:

1.  If possible, try an external TP tranceiver on the card.  It should work.

2.  Try an ELII-TP or ELMC-TP rev B in the same location.  It should work.

3.  Try moving the adapter to a shorter length wiring run of the network.
Shorter runs should not experience the problem.

Consult the ELMC-TP Adapter Guide for the maximum lengths allowed for
twisted pair wiring.  For reference, absolute limits are listed below.

     100 m     10Base-T or Lattisnet.  24 AWG wire.
     150 m     10Base-t w/3Com Hub.  22 AWG wire.
     175 m     3Com Hub extended distances. 22 AWG shielded wire.

