Subject: RE: Last Call for TCP Congestion Control I-D (IW>1)

From: Peter Ford <[email-masked]>
Date: Tue, 17 Nov 1998 11:45:19 -0800

Mark, Vern and William,

Given the following text in RFC 2414:

   This upper bound for the initial window size represents a change from
   RFC 2001 [S97], which specifies that the congestion window be
   initialized to one segment.  If implementation experience proves
   successful, then the intent is for this change to be incorporated
   into a revision to RFC 2001.

isn't the language in the -01 draft a little out of sync?

    IW, the initial value of cwnd, MUST be less than or equal to MSS
bytes.

    We note that a non-standard, experimental TCP extension allows that
    a TCP MAY use a larger initial window (IW), as defined in equation 1
    [AFP98]:

               IW = min (4*MSS, max (2*MSS, 4380 bytes))             (1)

    With this extension, a TCP sender MAY use a 2 segment initial
    window, regardless of the segment size, and 3 and 4 segment initial
    windows MAY be used, provided the combined size of the segments does
    not exceed 4380 bytes.  We do NOT allow this change as part of the
    standard defined by this document.  However, we include discussion
    of (1) in the remainder of this document as a guideline for those
    experimenting with the change, rather than conforming to the present
    standards for TCP congestion control. 

I believe the language in the draft should be modified to reflect the intent
and direction the Internet community is taking.  This is clearly documented
in RFC 2414.  May I propose that the paragraph from RFC 2414 be lifted and
used to replace the sentences in the last paragraph  starting with: "We do
NOT allow this change as part of the standard defined by this document.
However, ..."

The draft on TCP Congestion Control  should reflect the knowledge we have
gained since 1988, and indicate direction and rationale to those who read
the spec.

cheers, peter

---

From: Mark Allman <[email-masked]>
Date: Tue, 17 Nov 1998 15:19:23 -0500

>    This upper bound for the initial window size represents a
>    change from RFC 2001 [S97], which specifies that the congestion
>    window be initialized to one segment.  If implementation
>    experience proves successful, then the intent is for this
>    change to be incorporated into a revision to RFC 2001.

Peter-

RFC 2414 was published as an experimental RFC.  It shows promise as
a Good Thing, but being that it has been out only a couple of months
I don't think we have all that much implementation experience with
it right now (at least not much more than when it was published as
an experimental RFC).  I think that the larger initial window will
be appropriate to standardize in **A** version of 2001.  And, I hope
that implementation experience proves me right.  But, I don't think
the experience has shown larger initial windows to be a Good Thing
or a Bad Thing at this point.  And, therefore, I think that the
wording in the current version of the document is correct.

allman