Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!ut-emx!spurgeon From: spurgeon@ut-emx.UUCP (Bud Spurgeon) Newsgroups: comp.dcom.lans Subject: Re: Ethernet max length problems Keywords: repeaters? ethernet too long Message-ID: <18908@ut-emx.UUCP> Date: 28 Sep 89 14:15:11 GMT References: <634@elan.elan.com> <2829@orion.cf.uci.edu> <16069@umn-cs.CS.UMN.EDU> Reply-To: spurgeon@emx.UUCP (Bud Spurgeon) Organization: UTexas Computation Center, Austin, Texas Lines: 25 In article <16069@umn-cs.CS.UMN.EDU> peiffer@umn-cs.cs.umn.edu (Tim J. Peiffer) writes: >Why did our repeater not partition under a large impedance mismatch? I expect >that the repeater should have seen many collisions... If your wire had been completely unterminated the repeater would have stayed partitioned just fine. But as soon as the repeater can get ONE good packet onto the failing wire, it will stop partitioning. Then after >32 consecutive packet failures it will partition again (but still keep trying to send packets onto the partitioned segment) and if the segment isn't a *complete* lose it will succeed in transmitting a packet onto it and stop partitioning. Depending on how bad your wire mismatch/damage is this can happen quite rapidly and make it appear that the repeater hasn't partiioned the segment at all. As far as the hapless users on the "good" side of the repeater are concerned, it might as well not have tried since the effect is tons of collisions as the repeater jams each failing packet and keeps counting till >32 is reached, then goes back into transmission after one good packet gets through, then starts jamming again, over and over. The moral seems to be that auto-partitioning is good for isolating nice solid wire failures, but if your failure is marginal then the auto-partitioning feature can't really protect you from it.