Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!husc6!purdue!gatech!amdcad!phil
From: phil@amdcad.AMD.COM (Phil Ngai)
Newsgroups: comp.dcom.lans
Subject: Re: Can Ethernet TCP/IP lock up?
Keywords: Heartbeat, jabber
Message-ID: <21712@amdcad.AMD.COM>
Date: 21 May 88 18:10:22 GMT
References: <299@fedeva.UUCP> <21674@amdcad.AMD.COM> <21680@amdcad.AMD.COM> <10303@ulysses.homer.nj.att.com> <21695@amdcad.AMD.COM> <3366@saturn.ucsc.edu>
Reply-To: phil@amdcad.UUCP (Phil Ngai)
Organization: Advanced Micro Devices
Lines: 35

In article <3366@saturn.ucsc.edu> eshop@saturn.ucsc.edu (Jim Warner) writes:
>In article <21695@amdcad.AMD.COM> phil@amdcad.UUCP (Phil Ngai) writes:
..This is a very important principle. I call it the "testing your
..spare tire" policy. Redundancy without an alarm to notify you
..when it has been invoked is very dangerous.
..
.Not quite.  If a transceiver's jabber circuit causes it to disconnect
.it will stay disconnected until either (a) the power is cycled or
.(b) is is explicitly reset over control lines that are not implimented

Sorry about that, my brain was going faster than my fingers at that
point. There are two concerns. First, you want a way to test backup
features which are normally rarely put in use. Second, you want to
be notified when a backup feature is put in use.

An example of the first is the heartbeat signal for the transceiver's
collision detect function. There is nothing similar for jabber.

An example of the second would be for the OS to complain if it wasn't
receiving heartbeat. As you have noted, jabber is very noticable when
it trips, so that is not a problem. 

.I have a transceiver cable breakout box.  I used it on several
.systems to disconnect the collision pair between several systems
.and their transceivers.  I expected to see messages start appearing
.on the console.  What I got instead was silence.  The OS was never
.notified.  I did this to a 3com 3C501 and ran the self test that
.came on a diskette with the interface.  It told me that my system
."passed with flying colors."  

I think that says something about 3Com.
-- 

I speak for myself, not the company.
Phil Ngai, {ucbvax,decwrl,allegra}!amdcad!phil or phil@amd.com