[Tsvwg] new revision of early retransmit available
Mark Allman <mallman@grc.nasa.gov> Fri, 22 August 2003 16:28 UTC
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To: tsvwg@ietf.org
From: Mark Allman <mallman@grc.nasa.gov>
Reply-To: mallman@grc.nasa.gov
Organization: BBN Technologies/NASA GRC
Song-of-the-Day: Ticket to Ride
Date: Fri, 22 Aug 2003 12:27:19 -0400
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Subject: [Tsvwg] new revision of early retransmit available
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Folks- We have just sent a new version of the Early Retransmit internet draft to the secratariet. It should appear in the archives in a couple of days. It is available from: http://roland.grc.nasa.gov/~mallman/papers/draft-allman-tcp-early-rexmt-02.txt now. The largest change in the document is that it now includes a variant that uses SACK information to make ER more robust. The problem that we have found is that the instances where ER will help are windowed quite a bit when it just counts duplicate ACKs. First consider two states the reciever could be in.... * S1: the receiver has ACKed all data received * S2: the receiver has received a packet but is delaying its ACK for another arrival (or the timer) When the receiver is in S1 and an out-of-order segment arrives a dup ACK will be triggered and ER will work nicely (or, as nicely as possible). When the receiver is in S2 and an out-of-order segment arrives the receiver will send an immediate ACK, but it will not be a duplicate -- but, rather it will cover previously unACKed data. In this case, ER is not in a happy place because it expects a duplicate ACK from all but one of the segments outstanding. So, we (meaning Josh, really) figured out that if we leveraged SACK information we could just tell when all but one packet has arrived at the receiver and key on that for ER, rather than try to count duplicate ACKs. (Because even if the ACK for out-of-order data is cumulatively ACKs previously unACKed data (i.e., is not a dup ACK) it will still have SACK information indicating what packet triggered the ACK.) This scheme seems more robust. At the moment both schemes are in the draft. But, we are seriously considering ripping out the version that does not use SACK on the grounds that if you're not using SACK and you are interested in good loss recovery in 2003 then you really can't be all that interested. (Recent measurements: I am seeing > 90% of web clients support SACK at a web server I am watching. I ran tbit against 61,000+ web servers and 65% support SACK.) We'd be interested in getting feedback on any of the above issues (and the text of the draft itself, of course). Thanks! allman _______________________________________________ tsvwg mailing list tsvwg@ietf.org https://www1.ietf.org/mailman/listinfo/tsvwg
- [Tsvwg] new revision of early retransmit available Mark Allman
- Re: [Tsvwg] new revision of early retransmit avai… Mika Liljeberg
- Mark Allman [Re: [Tsvwg] new revision of early re… Mika Liljeberg