Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!fxgrp!mr-frog
From: mr-frog@fxgrp.UUCP (Dave Pare)
Newsgroups: comp.protocols.tcp-ip
Subject: fragmenting broadcasts
Message-ID: <1041@fxgrp.UUCP>
Date: 2 May 89 21:44:07 GMT
References: <8904291828.AA18506@poincare.geom.umn.edu> <66@jove.dec.com> <May.2.11.51.47.1989.1419@ron.rutgers.edu>
Reply-To: mr-frog@fxgrp.UUCP (Dave Pare)
Organization: FX Development Group, Inc., Mountain View, CA
Lines: 45

I was the original poster that started this whole mess, and I suspect
if I'd added some context, I could have made things somewhat clearer.
Asking people to comment in an information vacuum was the wrong approach.

So here is some context:

My task is to distribute fairly large volumes of data to sites on
an ethernet.  One central host takes an external data feed, massages
it a bit, and then sends it out on the main wire.  In this application,
each host on the wire is interested in receiving a major portion of
what is being broadcast.  No hosts are uninterested in receiving
these broadcast messages.

The network is being used as a broadcast data distribution mechanism.
My program will be the only broadcaster, perhaps with the exception
of occasional vendor-supported broadcasters like rarpd.

Given that I know what I'm doing, and that every host really and truly
does want to see almost all the data broadcast, can people understand
why I am perturbed by the limitation on the size of my broadcast
transmissions?

I don't dispute that on a general-purpose computing network, it is
best to have the general rabble restrained by rigid host requirements
which limit the ability to do mischief.  I don't believe that I or the
clients who purchase our product fit the above description, and so
in this case I feel frustrated by the restrictions.

So, with all this in mind, do people still maintain that the most
reasonable way for the network to behave is to force my program to
perform the fragmentation/reassembly task in user code?  That means
I have to switch into kernel mode for each 1k packet, instead of
buffering things up and sending 4k, or 8k packets.

Another thing: I've never seen a datagram get lost on a LAN.  They
do get discarded when the receiving process can't drain the receive
buffer space quickly enough, though.

I really don't want to sound like a whiner.  I like UDP.  I'm just
hoping that Someone Who Matters will read this posting, and decide
that the best way to interpret the Host Requirements document is to
have a default setting be "no fragmentation", but allow a kernel
global variable to remove this restriction.

Dave Pare