Subject: Re: [Tsvwg] Re: Diffserv codepoint seems strange for Re-ECN <draft-briscoe-tsvwg-re-ecn-tcp-00>

From: Sally Floyd <[email-masked]>
Date: Thu, 15 Dec 2005 16:14:31 -0800

Armando -

>Overall, I agree with most of your comments, but...
>
>Sally Floyd wrote:
>> The ECN nonce would be useful for more than just "certain large
>> senders".  For example, our measurement study of 80.000 web servers
>> ("Measuring the Evolution of Transport Protocols in the Internet",
>> April 2005 CCR, "http://www.icir.org/tbit/") found only almost all
>> of the web servers use appropriate congestion contron in TCP
>> connections, halving the congestion window in response to packet
>> drops.  I would imagine that most of these 80.000 web servers would
>> also find the ECN Nonce useful to verify compliance from receivers.
>
>I'm not sure I agree. Content providers mainly care about user
>experience, which means the state of the network is only important when
>it affects them and their receivers. If a sender has reason to believe
>that competing flows at the bottleneck point will most likely be from
>other sources, the sender may take its chances by not using ECN nonce.
>On the other hand, if the competing flows are likely to come from the
>same sender, then it definitely makes sense to try to enforce ECN
>compliance from receivers.

Yep, I agree.  But I would assume that the second of the two cases
above is not infrequent, e.g, congestion from competing flows
from the same web server.

In particular, the web server might be paying for the bandwidth of
its access link, so it might have an incentive that the bandwidth
of that access link be used effectively.  In particular, if there
is congestion on the web server's access link, then the web server
might have a stake in the use of effective congestion control, as
appropriate, by the users.

- Sally
http://www.icir.org/floyd/

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