Just how big a load are UDP broadcasts?

I run a small network of small sites, including a couple in the
Adirondacks with 56k feeds. When a user of one of these sites uses
one of the UDP audio or video services it drives the 56k to 100%
saturation (load 255/255) and makes the site unusable for everyone
else.

Recently I "solved" this problem by blocking this traffic at the entry
port for my T1 feed. To my surprise, both the average and peak
traffic on the T1 dropped by a factor of 3, although less than 2% of
my users complained.

Traffic on my T1 wasn't the issue, but this has me wondering: how much
of the Internet congestion my users do complain about is due to UDP
audio/video services?

In my very limited view of the world, UDP is a very poor network
citizen among protocols. Am I wrong in that view?

Does nobody else even care that dialup users can request streams of
far more packets than can go down their dialup lines?

If not, I might as well let my own users do this too - join the merry
party, burn bandwith across the net with traffic you can't receive ...

Is this a case of 14.4k users requesting 28.8k audio UDP streams or is the
problem more widespread?

The feedback loop for this branch of the software industry is strange
because the network providers need to be the ones pushing for the software
publishers to minimize bandwidth usage, yet the customers/end-users of
these companies don't give a direct hoot.

It might be time for something like a "Bandwidth Conservation Society"
which serves as a watchdog group that pressures software publishers and
bandwidth users in general, to use the net wisely. A BCS logo could be
given to those that pass certain criteria and customers/end-users could be
taught to look for such a logo.

Chris Caputo
President, Altopia Corporation

It's all their already.

http://www.bcs.org

All you have to do is get them to add wasteful use of UDP to their agenda.

Michael Dillon - ISP & Internet Consulting
Memra Software Inc. - Fax: +1-604-546-3049
http://www.memra.com - E-mail: michael@memra.com

I can't believe I just posted that. Let's try again...

It's all there already.

http://www.infohiway.com/way/faster/

All you have to do is get them to add wasteful use of UDP to their agenda.

Michael Dillon - ISP & Internet Consulting
Memra Software Inc. - Fax: +1-604-546-3049
http://www.memra.com - E-mail: michael@memra.com

> Does nobody else even care that dialup users can request streams of
> far more packets than can go down their dialup lines?

Is this a case of 14.4k users requesting 28.8k audio UDP streams or is the
problem more widespread?

The case where I first ran into this was CU-SeeMe between a univerity
student, apparently on at least a T1, and a 14.4 dialup. I don't have
a precise measure of the traffic, but it was around 30% of capacity of
what was then a 384 incoming feed. Not much of it fit down the
dialup, but it all went through Pennsauken.

It might be time for something like a "Bandwidth Conservation Society"

I think "conservation" is not the right concept. The bandwidth is
there to be used, and people ought not to be discouraged from using
it. I don't think flooding a destination with traffic it can't
receive counts as "use".

Sending no more than will actually arrive is only a minimal
requirement, not a sufficient standard. Having observed streaming UDP
push TCP completely aside on a 56k, I imagine much the same thing
happens on any congested link: TCP will yield bandwidth until UDP has
all it needs to get the entire UDP flow through.

Sending no more that it's "fair" even to try to get through the most
congested portion of a route would be a much more stringent standard,
one that TCP meets according to my admittedly not very deep
understanding of how things actually work.

Of course, if simplistically applied, such a standard would completely
kill any realtime-ish applications on today's Internet, and I don't
want to do that. Maybe an answer could lie in the definition of
"fair" involving a longer time scale - like it's ok to use UDP to
bulldoze your "realtime" flow though a congested link when competing
with lots of TCP flows if you don't expand to use more than your "long
term share" when not competing with many TCP flows (where the
assumption is that what's important for most TCP flows is the total
duration, not intra-flow speed variations).

Now that I've completely wandered off the deep end, I'd really like to
have some people who know what they're talking about say something.
All I really know for sure is that a lot of audio/video traffic
crosses the net only to not be able to go down the last phone line. I
think it's likely to get worse real fast:
        28.8 --> 14.4
        ISDN --> 28.8, 14.4

Somebody in the office pointed out that what's needed in this area is
effectively an Applications Requirements RFC, similar to the Router
and Host Requirements RFCs. In the good (but somewhat boring) old
days, there wasn't really a lot of applications outside the normal
UNIX and TCP-based environment, with multicasting being the exception
(and this one carefully tunneled and monitored), so Router and
Host Requirements were all that was needed.

To what extent such an RFC actually would be useful, I don't know. You
mention CU-SeeMe, which we got hit by very badly, starting almost a
couple of years ago. That was with the earlier version, where a user
could request up to 640kbps of UDP data to be sent to him,
irrespective of his own bandwidth and whatever else might want to run
over the same lines. It only takes 2-3 users of an application like
that to hog a T1 or an E1. We had a longish discussion/battle on the
mbone list about this a year or something ago (hi Jon), and found it
very difficult (at least to start with) to get even the Internet R&D
community to understand the problems. In the end I think I can say
we won the day, and the CU-SeeMe developers have since then put in
congestion control, which actually works pretty OK; the application
still eats a lot of continuous bandwidth, but it's limited roughly to
the thinnest pipe along the path, and since most Kool Cyber Dudes are
on dial-up, no real/immediate damage is being done.

But getting the attention of developers of Kool Cyber Applications
won't necessarily be easy, not least because many of them really
don't have too much idea about background, engineering, whatever.
Was it Vocaltec that circulated this ad "Talk for FREE over the
Internet"? I think so, but it doesn't matter anyway; I have seen
other people dabble in "TCP accelerators", which is a "more powerful"
TCP implementation in a proxy setting, adding "thrust" to "weaker"
TCP implementations on hosts behind it, getting more throughput on
congested lines.

In the end all of this is just an arms race and there is a risk that
it will gradually lower network service quality if shared capacities
aren't kept up to meet demand (polite and considerate applications
and protocols are much better at coexistence; aggressive dittos will
end up wasting large amounts of resources). This in turn costs more
money, which the users of the applications don't particularly want to
part with (after all, they're supposed to be able to do whatever for
free, that's what the vendor said).

There is clearly scope for enlightened members of the press to try to
prevent Internet application developers from repeating the success of
50s and 60s car makers. That would actually be a valuable contribution
to a healthier Internet industry.