Path: utzoo!attcan!uunet!husc6!cmcl2!nrl-cmf!ames!pasteur!ucbvax!nynexst.COM!sholom
From: sholom@nynexst.COM (Sholom Fried)
Newsgroups: comp.sys.proteon
Subject: Re:  problems with serial lines
Message-ID: <8807221739.AA23355@psl9.nynexst.com>
Date: 22 Jul 88 17:39:57 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 28


>What appears to happen is that the link will go down (in one direction),
>the p4200 will detect a Maintenance Failure, and go into Self Test.  When
>this happens, virtual circuits across the link will die (especially
>if the circuit is using KEEPALIVEs, such as rlogin).  Sometimes the link
>will stay down long enough that routes to that subnet will time out, but
>this is unusual.

Your problem sounds very familiar. We have a testbed of P4200s in our
lab here, and we're also involved with NYSERNet, which is currently based on
P4200s - and in both cases we've experienced the same thing. Reducing these
link failures is very important for NYSERNet, where they may be killing
lots of virtual circuits.
We haven't completely isolated the causes of these "interface flappings"
although we've found some contributing factors.
Cables - in the lab we've found that poor cables (not manufactured to
V.35 spec - balanced lines not twisted together) can cause interface fluttering
particularly if they're long - 20+ feet. Even in shorter cables this frequently
contributes to high crc and framing errors. Some people claim that the full set
of pins, when not used, add to the problem by adding inductance. You may want
to look out for other emi type problems.

If you find anything significant let us know! Good luck.

Sholom Fried
NYNEX S&T
914-287-5159
sholom@nynexst.com