Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!uunet!decwrl!nsc!voder!blia!ted
From: ted@blia.BLI.COM (Ted Marshall)
Newsgroups: comp.dcom.lans
Subject: Re: Do DELNI's cause collisions?
Summary: Close but not quite
Message-ID: <11702@blia.BLI.COM>
Date: 29 May 90 20:15:18 GMT
References: <145340@felix.UUCP>
Organization: Britton Lee, Los Gatos, CA
Lines: 28


If a DELNI is in "global" mode and the transceiver connected to the global port
is wired for SQE test (heartbeat), the heartbeat signal is passed down to ALL
of the local ports. In other words, when any of the stations finishes a
packet transmision, all of the stations on the DELNI see the heartbeat "blip"
on collision detect pair.

This condition will cause few, if any, problems because most Ethernet stations
don't care about collision signals when they aren't trying to transmit. Also,
because the blip comes early within the required 9.6us inter-packet gap,
stations waiting to transmit shouldn't be affected either.

That is NOT to say that there isn't Eathernet hardware on the market today
that won't be affected. Devices that don't wait the full inter-packet gap
before transmitting or otherwise are brain-dead in terms of following the
specifications, for example. Also, anything that isn't a simple station,
such as a repeater or bridge, may be affected. Those aren't supposed to be
connected to a transceiver that generates heartbeat anyway (I believe).

Also, any kind of Ethernet analyzer that counts collisions that is connected
to a DELNI will most likely count a collision for each heartbeat it sees. That
is, for each transmition by another station on the DELNI. This is generally
where rumors about extra collisions generated by DELNIs come from.

-- 
Ted Marshall          ...!ucbvax!mtxinu!blia!ted  <or>  ted@blia.bli.com
ShareBase Corp., 14600 Winchester Blvd, Los Gatos, Ca 95030     (408)378-7000
The opinions expressed above are those of the poster and not his employer.