Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!think.com!sdd.hp.com!hplabs!nsc!voder!berlioz.nsc.com!mikel From: mikel@berlioz.nsc.com (Michael G. Lohmeyer) Newsgroups: comp.dcom.lans Subject: Re: Ethernet "heartbeat" Message-ID: <1991May20.185642.6704@berlioz.nsc.com> Date: 20 May 91 18:56:42 GMT References: <105002@sgi.sgi.com> <1991May19.133507.1@ptavv.llnl.gov> Sender: news@berlioz.nsc.com Organization: National Semiconductor Corporation Lines: 36 In article <1991May19.133507.1@ptavv.llnl.gov> oberman@ptavv.llnl.gov writes: >The bottom line is that SQE is badly understood. This thread just goes to prove >it. It was not designed to detect loose cables, although it's quite good at it. >It is there to detect the failure of MAUs and especially collision detect >circuitry. And, since MAUs tend to be very reliable, people don't see the >importance of this, so they don't bother with SQE. That's a lazy action. It >violates the standard (8802-3), and that alone is, IMHO, a reason to use it. When I originally said that heartbeat could be used to detect a loose cable, I was saying that if the transmit and receive pairs were touching and the collision pair was not, then the lack of a heartbeat at the end of a transmission will signify that the collision lines were not touching. I should have mentioned, as is said above, that the main purpose of heartbeat is to test the MAU's collision (or SQE) circuitry (which includes the cable). Sorry to have caused any confusion. In any case, in my opinion, you should not disable the SQE. Also, it would be nice if driver software, in general, reported heartbeat errors, but, as has been stated, this is not the case. An interesting point to make about heartbeat and SQE, as many of you probably already know, is that SQE (which was defined in IEEE 802.3) stands for Signal Quality Error. SQE does not specifically stand for heartbeat (which is a term that comes from Ethernet II). As the name implies, SQE signifies an error in the signal transmitted or received. So, collisions and heartbeat are subsets of SQE. I bring this up because most MAUs, etc. always talk about disabling SQE. Taking this literally means that you are disabling the collision detection circuitry, not just heartbeat. Of course, the SQE disable on these MAUs means to disable heartbeat, not the entire collision circuit. That's my trivia for the day. Mike ------------- Mike Lohmeyer mikel@berlioz.nsc.com Local Area Networks National Semiconductor Corporation (408) 721-8075