[Iccrg] proposed Compound TCP review

[Eddy, Wesley M. (GRC-RCN0)[VZ]]

Attached is a proposed RG review of the Compound TCP draft that we were
asked to consider the safety of for experimental deployment on the
Internet,
on behalf of TCPM.

We had several mails on-list about this in recent months, and now that
discussion has slowed down, I believe we may be ready to close on this
and submit an official RG review to TCPM.  Please review the attached
text
for accuracy, and comment on it.  I drafted it with help from the list
archives, and believe it captures a consensus that the RG has at a
high-level.

Replies via email that either support this, or suggest clarifications,
improvements, or fixes are welcomed at this time.  I also set aside
time during the Philadelphia meeting that we can use to discuss or
revise this in real-time face-to-face.  Also, let us know if it is
wildly inaccurate or doesn't capture your individual concerns at a
high-level.  Thanks for your help.
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In July 2007, the ICCRG began reviewing the Compound TCP
congestion control technique described in
draft-sridharan-tcpm-ctcp-00 in terms of its safety for
widespread experimental deployment on the public Internet.
This review was conducted as an input to the IETF TCPM
working group, where the draft was being considered for
possible Experimental publication.

Based on initial RG comments, an update to the original
internet-draft was published.  Based on further RG comments,
another update is expected that contains several clarifications
(itemized at the end of this document).  This review assumes
that those changes are made.

After reviewing the draft and a number of other documents
with results from testing and simulation, three public
evaluations were submitted to the ICCRG by RG participants.
Several follow-on messages and comments were submitted by
these and other RG participants.  The RG seems to have
consensus that (given the expected draft clarifications)
the Compound TCP mechanism is safe for experimental deployment
on the public Internet.

Its novelty from the current Standards Track congestion control
techniques is that Compound TCP also contains a delay-based
component.  Compound TCP's design only utilizes the delay-based
component when the loss-rate is low and the congestion window
has been able to grow large already based on the current
Standards Track mechanisms.  This was noted by some reviewers
as a major inspiration of confidence.  The simulation results
and analysis made available were also helpful, but were not found
to be overwhelmingly convincing.

Expected changes from the 01 draft version:

1. Clarify how RTT samples are captured (1323 or some other filter).

2. Clarify definition of baseRTT. (noted by 2 reviewers)

3. Clarify definition of "round" in dwnd update (is it in terms of
   RTT or cwnd worth of packets).

4. What happens to dwnd during slow-start, and when is slow-start
   exited?

5. Clarify dwnd update parameters and specific values or ranges
   that are safe for use (alpha, beta, eta, k)
   (noted by 3 reviewers)

6. Be precise about clipping dwnd so that it cannot become negative

Public reviews from:
Wesley Eddy (Nov 1, 2007)
Mark Allman (Nov 29, 2007)
Doug Leith (Jan 16, 2008)

additionally, several thread comments from:
Lachlan Andrew
Michael Welzl
Dino-Martin Lopez-Pacheco