Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!uunet!munnari.oz.au!murtoa.cs.mu.oz.au!ditmela!latcs1!wcc!tom From: tom@wcc.oz (Tom Evans) Newsgroups: comp.protocols.appletalk Subject: Re: Localtalk 30 node limit Message-ID: <449@wcc.oz> Date: 10 Nov 89 08:01:27 GMT References: <2548@aecom.yu.edu> <429@wcc.oz> <1989Nov2.013604.24598@polyslo.CalPoly.EDU> Organization: Webster Computer, Melbourne, Australia Lines: 42 In article <1989Nov2.013604.24598@polyslo.CalPoly.EDU>, dorourke@polyslo.CalPoly.EDU (David M. O'Rourke) writes: > tom@wcc.oz (Tom Evans) writes: > >There are better reasons to use LocalTalk routers before that limit is > >reached. > > I don't understand why you divide the bandwidth. Each node doesn't get > assigned a chunk of the bandwidth. When one node is using the network it > has all of the network bandwidth availible to it for the duration of that > particular packet's transmission time. The problem with lots of nodes > on any contention {sp??} based network is that as you add nodes to the > network the probability of a collision, and hence a re-transmission, goes > way up. When you get collisions you have to backoff and retransmit which > waste more bandwidth and lowers overall throughput. Two points. With a high speed network (Ethernet), it takes a fairly busy host to grab more than a fraction of the bandwidth, and thus a lot of hosts till it's "full". I can grab 54% of a LocalTalk network with ONE MAC SE! I just copied a 1.9Mb stack from a server and it took 127 seconds - that's 14.7kbytes/sec. LocalTalk's theoretical max without ANY OVERHEAD is 28kbytes/sec. If you have two Macs doing file transfers, Application launches or heavy printing, they start stomping each other. You're sharing bandwidth REAL EARLY. The only soltion to this is to add LocalTalk Routers where needed. With Ethernet you do get a loss of effective bandwidth as the traffic and the resulting collision rate go up. With LocalTalk, there are no "detected" collisions. Collisions only occur between the short "RTS" packets which are 3-byte (ok, 8.5 bytes on-the-wire) packets. A data packet is up to 600 bytes, so you don't lose as much to collisions as you'd expect. Yes, I agree totally about the number of connectors in a 30-node network. --------- Tom Evans tom@wcc.oz.au | Webster Computer Corp P/L | "The concept of my 1270 Ferntree Gully Rd | existence is an Scoresby VIC 3179 Australia | approximation" Australia | 61-3-764-1100 FAX ...764-1179 | D. Conway