Subject: [tcpm] rfc2581bis [1]: setting ssthresh

From: Mark Allman <[email-masked]>
Date: Tue, 13 Feb 2007 10:00:31 -0500

Folks-

We have just submitted a new rev of 2581bis.  We fixed some minor things
that folks flagged.  In addition, we made two substantive changes, which
I am putting into two different emails.  

The draft should pop out of the usual places soon, but until then you
can slurp a copy from:

    http://www.icir.org/mallman/papers/draft-ietf-tcpm-rfc2581bis-02.txt

The first issue we discussed a while back (in Montreal) and I believe
the room had decent consensus on this, but it took a while to roll it
into the draft and therefore verify it here on the list.

The change...  On the first retransmission of a segment with sequence
number X the ssthresh is set to half the FlightSize as it always has
been specified.  However, on subsequent retransmissions the same segment
ssthresh is held constant.  RFC 2581 was ambiguous on this point.
However, the intent was that ssthresh be halved on each retransmit.
However, the WG seems to have consensus that this is not really required
and the upside is that we do not doom connections to linear growth hell
for ephemeral network conditions.

Why I think this is OK is that if it is a problem that we held ssthresh
constant and did not drop it then we will quickly learn of this by
taking more loss and therefore collapsing ssthresh further.

If folks feel that we have taken the wrong approach in the document,
please yell.

Thanks,
allman

Content-From [email-masked] Tue Feb 13 10:07:45 2007
To: [email-masked]
From: Mark Allman <[email-masked]>
Organization: ICSI Center for Internet Research (ICIR)
Song-of-the-Day: Whole Lotta Love
Date: Tue, 13 Feb 2007 10:00:31 -0500
Subject: [tcpm] rfc2581bis [1]: setting ssthresh
Reply-To: [email-masked]
 
Folks-

We have just submitted a new rev of 2581bis.  We fixed some minor things
that folks flagged.  In addition, we made two substantive changes, which
I am putting into two different emails.  

The draft should pop out of the usual places soon, but until then you
can slurp a copy from:

    http://www.icir.org/mallman/papers/draft-ietf-tcpm-rfc2581bis-02.txt

The first issue we discussed a while back (in Montreal) and I believe
the room had decent consensus on this, but it took a while to roll it
into the draft and therefore verify it here on the list.

The change...  On the first retransmission of a segment with sequence
number X the ssthresh is set to half the FlightSize as it always has
been specified.  However, on subsequent retransmissions the same segment
ssthresh is held constant.  RFC 2581 was ambiguous on this point.
However, the intent was that ssthresh be halved on each retransmit.
However, the WG seems to have consensus that this is not really required
and the upside is that we do not doom connections to linear growth hell
for ephemeral network conditions.

Why I think this is OK is that if it is a problem that we held ssthresh
constant and did not drop it then we will quickly learn of this by
taking more loss and therefore collapsing ssthresh further.

If folks feel that we have taken the wrong approach in the document,
please yell.

Thanks,
allman

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