Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!munnari.oz.au!wcc!tom From: tom@wcc.oz (Tom Evans) Newsgroups: comp.protocols.appletalk Subject: Re: Enhanced LocalTalk (was: Mac Booster Modules) Message-ID: <526@wcc.oz> Date: 18 Dec 89 07:21:31 GMT References: <6662@imag.imag.fr> <24772@cup.portal.com> <9241@hoptoad.uucp> Organization: Webster Computer, Melbourne, Australia Lines: 78 In article <9241@hoptoad.uucp>, tim@hoptoad.uucp (Tim Maroney) writes: > bordier@imag.imag.fr (Jerome Bordier) writes: > >>In November BYTE (p.219), Tom Thompson states that "the faster > >>DaynaTALK and FlashBox modules can coexist (with Macs not so > >> equipped) > >> > >> (my local distributor told me that > >>any Mac in one zone must have the booster module). > > Yes, it is true, at least of FlashTalk. FlashTalk Macs can coexist > with LocalTalk Macs. I don't know about DaynaTalk. Your distributor > done you wrong. Listen to your distributor (see below). > In article <24772@cup.portal.com> MacUserLabs@cup.portal.com (Stephan > - Somogyi) writes: > >Non-enhanced nodes usually can't see when enhanced nodes are > >transmitting, and will therefore step all over enhanced traffic. This, > >obviously, messes things up a bit. > > A rather vague and misleading phrase. Yes, LocalTalk Macs will step on > FlashTalk packets, requiring retransmission. However, this does not > cause any serious problems, other than some performance degradation. Some? SOME!!!??? How about 95% degradation being "some"? I've had to cope with a network that was having "some" packets stepped on, and it wasn't pretty. Let's put some real numbers to it. Machine "A" and "B" communicating using ATP - file copy operation at say 20kbytes/sec. This corresponds to 40 packets/second, all maximum length, and taking up 30% of the FlashTalk bandwidth at 700,400 bits/sec. We now talk from a slow Mac to a LaserWriter, neither of which can see the high speed traffic and stands a 30% chance of killing a fast packet per slow packet. We're running at a reasonable PAP rate of 10 packets per second. We are now killing Fast packets every 0.3 seconds or so. This incurs a 2 second timeout-retry from ATP. We're now sending 12 fast packets in 0.3 seconds and getting stomped for 2 seconds instead of sending 40 per second. 12/2.3 : 40/1 is an 87% slowdown. Some? Let's say the packet that gets clobbered is an ATP TREL packet (the ATP XO sequence is TREQ, TRSP, TREL). Between 10% and 30% of our packets are TREL's (but they're shorter than the data packets - about 30 bytes). For CAP, each TREL dropped incurs a 30 second stall - not a nice thing to witness. With AppleShare, you have two listeners on the socket, so you can drop ONE TREL per 30 second period without penalty. Or else you get the difference. With this added, you're probably up to 90% to 95% performance degradation. And that was with ONE FlashTalk session and ONE LocalTalk session. Jerome's distributor knew what he was talking about. > The real issue with these acceleration products is that they simply > don't deliver much extra performance. Even between two accelerated > Macs on the same network, you'll be lucky to get 1.5 speedup, much less > the three times one would expect from a naive application of the > network bandwidth improvement. Maybe the real advantage is that the physical cable can now handle THREE times the volume of traffic. Like three times as many Macs performing simultaneous data transfer before the net clogs up. Think of it as the difference between a one-lane and a three-lane road. Not much difference at 2:00am (when programmers go to work :-), but a lot of difference to us ordinary folk during the rush hour. --------- 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 | approximation" Australia | 61-3-764-1100 FAX ...764-1179 | D. Conway 2109 O'Toole Avenue, Suite J SAN JOSE CA 95131 - 1303 CALIFORNIA 1-408-954-8054 FAX 1-408-954-1832