🚀 go-pugleaf

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.

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