Path: utzoo!attcan!uunet!husc6!think!ames!pasteur!agate!saturn!eshop
From: eshop@saturn.ucsc.edu (Jim Warner)
Newsgroups: comp.dcom.lans
Subject: Re: Can Ethernet TCP/IP lock up?
Keywords: Heartbeat, jabber
Message-ID: <3366@saturn.ucsc.edu>
Date: 20 May 88 21:13:32 GMT
References: <299@fedeva.UUCP> <21674@amdcad.AMD.COM> <21680@amdcad.AMD.COM> <10303@ulysses.homer.nj.att.com> <21695@amdcad.AMD.COM>
Reply-To: eshop@saturn.ucsc.edu (Jim Warner)
Organization: University of California, Santa Cruz
Lines: 26

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
in any products I know of.  Nothing more will be transmitted til the
fault is cleared by (a) or (b). I'd say that's pretty good notification
that the fail safe has tripped.

>The designers of Ethernet were concerned about this. That is why
>the version 2 has the "heartbeat" or collision presence test
>at the end of every packet.

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."  

jim warner