Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!amdcad!rpw3 From: rpw3@amdcad.AMD.COM (Rob Warnock) Newsgroups: comp.dcom.lans Subject: Re: Performance problems with a DESPR Message-ID: <25007@amdcad.AMD.COM> Date: 28 Mar 89 08:42:36 GMT References: <1349@ndmath.UUCP> Reply-To: rpw3@amdcad.UUCP (Rob Warnock) Organization: [Consultant] San Mateo, CA Lines: 35 In article (Eriks Rugelis) writes: +--------------- | >I have the following configuration set up, which seems to be 'legal' | >according to DEC's Network and Communications Buyer's Guide. | ...I would be surprised if DEC allowed you to plug a DESPR into a DELNI | why? well because the DESPR is a repeater and a DEC supplied DELNI operating | in 'local' mode generates heartbeat and repeaters cannot tolerate heartbeat; | a repeater operating in the presence of heartbeat will see excessive | collisions and will have the poor performance behaviour that you describe +--------------- Almost. What a repeater cannot tolerate is a multi-port which does heartbeat *incorrectly*, such as a DELNI. Doing heartbeat "correctly" here means that you only give a heartbeat [little burst of "collision" immediately following a transmitted packet] to the port which transmitted. I believe that DELNI's give back a heartbeat [heartburn?] to *all* ports when *any* port transmits. This is simply carelessness on the part of the designer(s). It takes all of $0.50 worth of logic per port (a non-critical one-shot) to do it right. +--------------- | solution? replace the DELNI with a similar box not made by DEC that allows | you to select/deselect heartbeat (i.e. I use Cabletron's MT-800's)... +--------------- ...or a box which does it correctly [by the above definition]. I'm not sure if the Cabletron does it right, either, but at least they let you disable heartbeat per port (which is enough). Rob Warnock Systems Architecture Consultant UUCP: {amdcad,fortune,sun}!redwood!rpw3 DDD: (415)572-2607 USPS: 627 26th Ave, San Mateo, CA 94403