Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!unisoft!mtxinu!taniwha!paul
From: paul@taniwha.UUCP (Paul Campbell)
Newsgroups: comp.protocols.appletalk
Subject: Re: does Mac barge into flashtalk?
Keywords: flashtalk
Message-ID: <325@taniwha.UUCP>
Date: 25 Feb 89 20:51:55 GMT
References: <20838@agate.BERKELEY.EDU>
Reply-To: paul@taniwha.UUCP (Paul Campbell)
Distribution: usa
Organization: Taniwha Systems Design, Oakland
Lines: 44

In article <20838@agate.BERKELEY.EDU> jim@insect.berkeley.edu () writes:
>A short piece on page 12 of InfoWorld, Feb. 20, 1989, by Mark Stephens
>entitled: "Tutorial. Appletalk Standard Present in All Macintosh Computers;
>But Access Has Its Price: Network Software is Slow" states that
>
>     "The major reason Appletalk is slow is that the Zilog serial
>     chip can be overwhelmed by clock pulses that arrive at rates
>     faster than 230.8 kbps.  When data is sent any faster than
>     that over the network,  Macs are prone to not detecting the
>     clock pulse, deciding there is no traffic, and barging into
>     conversations."
>
>Is there any truth to this?  If so, what implications does this have for
>protocols like TOPS Flashtalk on the same network as Macs?

What it really means is that the clock recovery ciruitry on the SCC
(phase locked loop) doesn't work at much over 230k .... I think that
both FlashTalk and DaynaTalk are both just external faster PLLs and clocks
(probably 2 chips and a crystal) plus extra software.

Most when an appletalk packet is received with CRC errs or timeouts
(ie a 'faster' packet on a slower interface or viceversa) it is discarded,
when you go to send something on the net you send a pulse on the net
just before starting the first packet which is intended to force a collision
on anyone else who is also trying to start to send a packet. (This is
because localtalk hardware can't really do Collision Sense like ethernet can).

One thing you should be aware of if you are going to run a net a 3 times
the speed is that collision detection (esp of the type mentioned above)
is only going to work on a net with a MAXIMUM size that is 1/3 that
of the maximum size of a 230k net. Also problems from terminations
and reflections are potentially worse (look over your net for loose 
connections, if you have a phonenet style cabling make sure all the termination
resistors are in the correct place, make sure you don't have long cable runs
near mains wiring or fluorescent lights etc etc


	Paul

-- 
Paul Campbell			..!{unisoft|mtxinu}!taniwha!paul (415)420-8179
Taniwha Systems Design, Oakland CA

    "Read my lips .... no GNU taxes" - as if they could tax free software