Subject: [Tsvwg] [email-masked]: I-D ACTION:draft-allman-tcp-lossrec-00.txt

From: Mark Allman <[email-masked]>
Date: Tue, 06 Jun 2000 12:54:10 -0400

Sally Floyd, Hari Balakrishnan and I have put together an
Internet-Draft that outlines a small set of changes to TCP that
makes loss recovery more robust in the face of small window sizes
(or a ton of ACK loss).  The I-D announcement is attached.  

We'd appreciate hearing any comments you might have, as well as any
references to related work that we may have unintentionally
overlooked.

Thanks,
allman

------- Forwarded Message

A New Internet-Draft is available from the on-line Internet-Drafts directories.

	Title		: Enhancing TCP's Loss Recovery Using Early Duplicate 
                          Acknowledgment Response
	Author(s)	: M. Allman, H. Balakrishnan, S. Floyd
	Filename	: draft-allman-tcp-lossrec-00.txt
	Pages		: 9
	Date		: 05-Jun-00
	
This document proposes two new TCP mechanisms that can be used to
more effectively recover lost segments when a connection's
congestion window is small, or when a large number of segments are
lost in a single transmission window.  The first of these
mechanisms, 'Limited Transmit', calls for sending a new data
segment in response to each of the first two duplicate
acknowledgments that arrive at the sender.  The second mechanism is
to reduce, in certain special circumstances, the number of duplicate
acknowledgments required to trigger a fast retransmission.

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-allman-tcp-lossrec-00.txt

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From: Jamshid Mahdavi <[email-masked]>
Date: 08 Jun 2000 09:45:22 -0700

Some minor clarifications/additions:

In section 2, it might be good to clarify what is the correct behavior
in the case where the retransmission threshold is > 3.  It says you
should send N-1 Limited Transmits, but it also says max 2 in the
example.

If the threshold is N packets, you might send N-1 LTs at an effective
window of cwnd-MSS.  After reaching N dupacks, you then drop to
cwnd/2.  For N=3, this happens quite quickly.  For larger N, there
might be concern about prologing congestion.

Some of the recent work on reordering has hinted at larger values for
this threshold, which is why I suggest adding a small amount of text
to clarify the standard and the possible concerns in this area.

In section 3, it would be nice to see a short "SHOULD" or "MAY" at the
beginning which specifies the algorithm.  Like 

"In the case where duplicate ACKs are detected, and there is no new
data to use for a Limited Transmit, and there are fewer than 4
segments outstanding, the sender MAY reduce the retransmit threshold
to N-1, where N is the number of packets outstanding".  

That is kind of rough, but I think something like that would clarify
exactly what the change to 2581 is in section 3.

--Jamshid