[Tmrg] Round table: Buffer sizes

[Lachlan Andrew]

Greetings again,

On 02/10/2007, Lachlan Andrew <lachlan.andrew at gmail.com> wrote:
> On 01/10/2007, Sally Floyd <sallyfloyd at mac.com> wrote:
> > some links that have been measured, a realistic mix means
> > 90% of data packets with 1500 bytes, with a mix for the
> > remaining data packets of 500 bytes, 4000 bytes, 200 bytes,
> > and the like.
>
> Since the TCP algorithms themselves determine the percentages of
> traffic, we should specify the traffic in terms of the number of
> flows   with each MTU, rather than the amount of traffic.  How about
> specifying 90% of flows use 1500-byte, and 10% of flows use 536-byte?

On second thoughts,  TSO and iperf's blocking themselves produce a
significant number of packets below the MTU.  If we have 100% of flows
with an MTU of 1500 and use TSO, we may automatically get 90% 1500
byte packets, and 10% smaller ones.

If we rely on this artifact, we should control for it (specify iperf
parameters?), and specify how to get comparable results in
simulations.

Having one flow with 10% of its packets small is very different from
having 10% of flows with all of their packets small.  Sally, I assume
the study you referred to was pre-TSO, but many of the smaller packets
could still have been runts from connections with larger MTUs.

Thoughts?

Cheers,
Lachlan

-- 
Lachlan Andrew  Dept of Computer Science, Caltech
1200 E California Blvd, Mail Code 256-80, Pasadena CA 91125, USA
Phone: +1 (626) 395-8820    Fax: +1 (626) 568-3603