[e2e] Question the other way round:

Vimal j.vimal at gmail.com
Sat Nov 16 08:43:56 PST 2013

I am not sure I entirely followed your previous email, but you seem to
point out that buffers are inevitable.  Yes, I think buffers are necessary
for good utilisation as arrivals are hard to predict.  In an ideal world
the buffer would be sized just about right to fully utilise link (assuming
that is something we care about).

As you pointed out rightly -- so far, again as far as I am aware -- we have
designed congestion control algorithms for a specific objective (which
seems hard enough).  From an optimisation perspective, the moment you have
two objectives, it is not clear, and not meaningful to talk about
"optimising" anything.  It exposes a tradeoff -- I don't think there is
hope of finding a universal scheduling algorithm that works best for all
objectives.  What is the 'right' tradeoff?  I have no idea.

You mentioned buffer sizing for low RTT and high throughput.  I think
achieving a particular objective might also need cooperation from
end-hosts.  Also, instead of one size fits all, you can have a hierarchical
scheduler setup:

- At the top level, divide bandwidth in some fashion between class A and B
(say equally)
- Class A has small buffers.
- Class B has large buffers.
- Flows that need low delay are directed to class A's queues.
- Flows that need high throughput are directed to class B's queues.

This way you can get a "bit" of both objectives while ensuring each class
gets a certain bandwidth guarantee.

On 16 November 2013 04:26, Detlef Bosau <detlef.bosau at web.de> wrote:

> One quick remark: As Vimal said, Len Kleinrock assessed his queueing
> systems with ONE metric.
> It may well be, that different flows have different objectives. One flow
> may prefer a short RTT, another one high throughput. Both is lumped
> together by using "the" one and only metric. Perhaps, a buffer for a
> wireless link will be made larger, when we want a high average
> throughput, and smaller when we want a smal RTT.
> With VJCC we first feed the net. Nearly regardless of the consequences.
> And afterwards, we try to escape the home made disaster.
> --
> ------------------------------------------------------------------
> Detlef Bosau
> Galileistraße 30
> 70565 Stuttgart                            Tel.:   +49 711 5208031
>                                            mobile: +49 172 6819937
>                                            skype:     detlef.bosau
>                                            ICQ:          566129673
> detlef.bosau at web.de                     http://www.detlef-bosau.de


More information about the end2end-interest mailing list