Subject: [Tsvwg] threshold retransmission

From: Mark Allman <[email-masked]>
Date: Wed, 03 Jan 2001 08:10:25 -0500

Folks-

Ethan and I have been chatting about the 'threshold retransmission'
scheme that Jamshid suggested we add to our SACK I-D
(draft-allman-tcp-sack-00.txt).  We both think the algorithm is a
good idea, as specified below:

  * For each octet we keep a counter that keeps track of the number
    of times something with a greater sequence number has been
    SACKed. 

  * When querying the scoreboard to figure out what to transmit we
    first look for the lowest sequence number that has been SACKed 3
    times (magic number is from the fast retransmit algorithm).  If
    we find no such segment we send a new segment.  If there is no
    new data to send we go back and retransmit the earliest missing
    segment even if it has not been SACKed 3 times (in an effort to
    keep the ACK clocking ticking).

We'd like to hear opinions on whether this sounds reasonable or not
(either on the list or privately is fine).  As soon as we figure out
if people like this or not we'll push out a new rev of the document
with the many fixes people have suggested to us.

Thanks!

allman

---
Mark Allman -- NASA GRC/BBN -- http://roland.grc.nasa.gov/~mallman/

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From: Matt Mathis <[email-masked]>
Date: Fri, 5 Jan 2001 13:10:01 -0500 (EST)

In light of people tinkering with dup ack thresholds, you should specify that
SACK thresholded retransmission uses the same threshold as fast retransmit, and
not wire in the number 3.

If done this way this way, future DSACK research can more easily permit TCP to
adapt to the the actual reordering.......

Thanks,
--MM--

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From: Ethan Blanton <[email-masked]>
Date: Fri, 5 Jan 2001 14:39:04 -0500

Matt Mathis spake unto us the following wisdom:
> In light of people tinkering with dup ack thresholds, you should specify
> that SACK thresholded retransmission uses the same threshold as fast
> retransmit, and not wire in the number 3.

I completely concur, and I will change the text in my working copy.
Ethan

-- 
I was young and foolish then, I feel old and foolish now.
		-- They Might Be Giants, "Ball & Chain"