Subject: Re: Fair Queueing as panacea

From: Curtis Villamizar <[email-masked]>
Date: Tue, 09 Apr 1996 14:33:53 -0400

In message <[email-masked]>, "Srinivasan Keshav" writes
:
> Juha, Curtis, and others have proposed that fair queueing (or some
> variant) is sufficient to provide a 'good-enough' quality
> of service (re: Zheng's complaint about the US-UK link). 
> While I would be the last to disparage fair queueing ;-)
> I think that fair queueing attempts _one_ possible resource
> allocation, that is, max-min fair. I believe that other 
> allocations, depending on pricing, are necessary.  Unfortunately, 
> this means we need WFQ, and I view the weights in WFQ 
> as a sort of reservation (one needs to somehow restrict the
> sum of the weights in order to provide bandwidth bounds, making them
> a 'resource'). So, fair queueing is not the whole solution, and it
> certainly does not do away with the need for some form of resource
> reservation. 
> 
> keshav

Keshav,

Since you have chosen to state what you think is my opinion (I don't
object to you doing so btw), there are a few things I'd like to point
out.  Before that some background on this particular US-UK circuit.

The US-UK link that Zheng was referring to may be an anomoly that is
hopefully going away.  The dynamics of traffic on this link was
discussed in detail on the end2end-interest list because this may
represent the most severely congested fairly large delay-bandwidth
path on the Internet.  At 4 mb/s and reports of on the order of 500
concurrent flows, each flow averages about 1KB/sec or just under 2
data packets per second with a 552 byte MTU.  TCP does not operate
very well at that level of congestion and may operate extremely poorly
when the router at each end supports relatively little buffering (one
of the primary areas of discussion).  Whatever the reason (those
interested in speculation can consult the archives at ISI), the result
is high packet loss.

Connectivity between Europe and the US still remains poor but there
are more than a half dozen IP providers with circuits across the
ocean, some more congested than others.

The artificially high prices of bandwidth are most pronounced in most
of Europe.  By comparison the US has a very competative market.  The
connection between continent is even worse since, while there has been
demand, few have been willing to fund bandwidth to meet the demand.
IMO This will change and US and European commercial providers may
partner and some large providers in the US have established a presence
in Europe and see a need for capacity to serve their direct customers.

If demand is far greater than capacity as is currently the case in
cross Atlantic traffic, then charging people who really care whether
their bits get through makes sense.  If capacity exceeds demand, as
was the case in the NSFNET backbone in 1993-1994 and much of 1995, and
may become the case in the US again later in 1996 or in 1997, then
charging for small reservations makes less sense.

I think you have misinterpreted some of what I've said on this and
other mailing lists.  I am not avdocating an entirely reservation free
Internet.  I'd like to see backbone capacities exceed the demand posed
by elastic and voice traffic such that charging for reservation was
only needed for large reservations, such as required for video
conferencing.  If that doesn't happen then charging for small
reservations will be needed for cost recovery.  This will be a more
substantial change from todays Internet charging model.

I've stated this clearly as "what I'd like to see happen" not "what
will happen".  I do happen to think it is a likely outcome, but I've
also pointed out how things change if this is not the outcome.  Lets
please all refrain from claiming to be able to predict the future.

I favor a simple approach toward providing reservations.  I personally
do not see the need for controlled delay.  It is fine to queue delay
sensitive reservations ahead of elastic or less delay sensitive
traffic.  A prioritized WFQ (small number of priority levels) seems
perfectly adequate with priorities chosen on the basis of delay
sensitivity and queue weights adjusted according to reservations and
best effort traffic hashed into its own set of queues (SFQ).

Regards,

Curtis

---

From: Masataka Ohta <[email-masked]>
Date: Wed, 10 Apr 96 11:10:07 JST

Curtis;

> If capacity exceeds demand, as

It's reservations which make less sense.

Charging for reservations still makes sense.

							Masataka Ohta