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From: vjs@rhyolite.wpd.sgi.com (Vernon Schryver)
Newsgroups: comp.dcom.lans
Subject: Re: Ethernet "heartbeat"
Summary: just another useless hardware or standards committee dodad
Message-ID: <104479@sgi.sgi.com>
Date: 16 May 91 17:26:18 GMT
References: <12164@uwm.edu> <1991May16.004523.21301@berlioz.nsc.com>
Sender: guest@sgi.sgi.com
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 35

In article <1991May16.004523.21301@berlioz.nsc.com>, mikel@berlioz.nsc.com (Michael G. Lohmeyer) writes:
>
>   ...[nice description deleted]...
> 
>      Most equipment supports it.  It is a spec for IEEE 802.3.  Generally,
> you want to make sure that the transceivers and MUXes that you get 
> do support it, and also allow you to turn it off.  Sometimes you need
> to be able to turn it off when connecting a MUX to a repeater for example,
> depending on the equipment you buy.
> 
> Mike Lohmeyer				mikel@berlioz.nsc.com
> National Semiconductor Corporation


From what I've seen, while most hardware more or less supports it, all
software ignores it.  If you write a BSD UNIX style driver, there's no
good place to count or report missing missing heartbeats.  You would not
want to printf on every missing heartbeat.  (I suppose you could do a
printf to the kernel or system once a day.)  If you take systems to major
trade shows, the people running the network always (in my experience)
refuse to listen to network problem reports until they've checked that the
transceivers have SQE turned off.

Perhaps this can be predicted from the fact that SQE is practically
optional, because it is not present in all of V1, V2, and 802.3, and
because all transceivers (that I've seen) allow you to turn it off.  What
is optional or commonly turned off cannot be relied upon.  Any error
reporting mechanism that cannot be relied upon, and is useful only for
detecting a relatively unlikely error is likely to atrophy.  Yes, I've
discovered and fixed loose connectors that heartbeat would have detected.
Has anyone ever had a system diagnose such a problem on its own?



Vernon Schryver,  vjs@sgi.com