Ethernet math (Was Re: MWC's Coherent - A Lemon...)

[Hwa Jin Bae]

In article <2871 at crash.cts.com> jca at pnet01.cts.com (John C. Archambeau) writes:
   When *I* start seeing consistant throughputs of more than 3 or 4 Mbits per
   second on an ethernet then I'll agree with you, but until then I write all of
   this off as the overhead of ethernet.

Kinda like saying: I don't care if there are bunch of people out in the real
world running 4.3 Tahoe TCP/IP on Sun 3/60's and getting ~8Mbits/sec on 
ethernets and I personally tell you that I have a system that can do
~6Mbits/sec on a busy ethernet.

   I don't care what your throughput is or
   what AST gets on his pair of Sun 3/60's, but what I see when I go and add or
   setup a network.

Like: if I can't figure out how to make my network go faster, it's not
my fault, but everyone else's for having done just what I can't seem
to figure out.  I can always just blame the "ethernet overhead" and
keep saying "I don't care."

Note, the max throughput limit on ethernet is a fixed value: 10 Mbits/sec.  
It is not something that changes.  What do you mean by "throughput" here
anyway?  The raw data transfer rate capacity of any task that talks to
your ethernet board will depend heavily on the way you wrote your ethernet
driver and the way your ethernet board itself is designed/constructed.
Sure, if you have some brain-dead ethernet implementation running with a
not-so-smart ethernet driver software, and your application is written
sloppily, your task-to-task data transfer rate will suffer.  This has nothing
to do with the channel capacity of a given segment of ethernet.  It has
everything to do with the quality of local implementation: the ethernet board,
the driver, the application/protocol code.

And, I'm telling you that if you have a nicely designed hardware (like an
onboard LANCE with enough dual-ported memory or fully arbited on-board
bus that lets you share main memory between CPU and LANCE) and an ethernet
driver that utilizes all these hardware design features by "loaning-out"
LANCE ring buffers to elimite extraneous copying, and a good protocol
implmenenation like 4.3 Tahoe BSD TCP/IP with all of Van Jacobsen's
optimizations, and a tightly coded application, ethernet will provide
you with ample bandwidth to guarantee ~6Mbits/sec even on a "real ethernet",
and more.  I have this type of systems running here.  Oh, I forgot: you don't
care.

What you tell me sounds like: well, I've plugged in all these fancy Sun
workstations and things into my ethernet and they're just pretty slow, so
don't tell me otherwise, I don't care, etc.  Hey, whatever makes you happy.
Enuf said.

hwajin
--
hwajin at daahoud.wrs.com