[e2e] Question about propagation and queuing delays

Ian McDonald iam4 at cs.waikato.ac.nz
Mon Aug 22 16:40:08 PDT 2005

Detlef Bosau wrote:
> David Hagel wrote:
>> This may sound like a naive question. But if queuing delays are so
>> insignificant in comparison to other fixed delay components then what
>> does it say about the usefulness of all the extensive techniques for
>> queue management and congestion control (including TCP congestion
>> control, RED and so forth) in the context of today's backbone
>> networks? Any thoughts? Are the congestion control researchers out of
>> touch with reality?
>> - Dave
> It depends.
> One answer is: Yes, they are.
> A more cynical answer is: If a lucky guy joins a PhD program, he must
> find a topic to write about.

As a lucky guy doing a PhD on congestion control I couldn't resist the bait :-)

I may be missing something but we need congestion control as long as we have networks. In the USA
and in Europe you may all have unlimited bandwidth available at virtually no cost to you but in the
rest of the "real world" it doesn't quite work like that. So as long as you are bandwidth
constrained you will need congestion control. I think others are out of touch of reality....

</flame bait off>

Seriously traffic can be constrained for many different reasons apart from backbones:
- link at other end (e.g. web server) is on a "slow" link
- mobile networks
- link between ISP and upstream ISP (a particular problem in NZ at the moment)
- slow speed link at consumer premises

Most backbones are over provisioned in the developed world but less so in more remote corners and
even less so in developing countries. I have seen presentations showing >50% packet loss in parts of
Asia and Africa on this list in the last few months - surely you need congestion control for that!

Remember congestion control is also about fairness on your own equipment as well - you want
competing flows to share nicely (unless you specify otherwise).



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