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F-RTO Algorithm for TCP: Detecting Spurious Timeouts

Learn about F-RTO algorithm, detecting spurious RTOs in TCP, sender-only principle, congestion control, handling out-of-order segments.

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F-RTO Algorithm for TCP: Detecting Spurious Timeouts

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  1. F-RTO Update<draft-ietf-tsvwg-tcp-frto-01.txt> Pasi Sarolahti Markku Kojo 59th IETF, Seoul, South Korea

  2. F-RTO Algorithm for Detecting Spurious RTOs • First individual version in June 2002 • Taken to tsvwg in October 2003 • Moves to tcpm • Spurious retransmission timeout • Timeout that would not have occurred if ACK arrived earlier • F-RTO looks for incoming ACK for segment that was not retransmitted • Sender-only algorithm • Follows congestion control principles • Can be used without TCP options • Send up to two previously unsent segments after RTO retransmission • New segments acknowledged => Spurious RTO • Duplicate ACKs due to out-of-order segments => not spurious RTO • SACK-enhanced version allows detection in presence of pkt reordering • Same principle is applicable with SCTP

  3. Changes from Individual-04 to tsvwg-00(draft-sarolahti-tsvwg-tcp-frto-04, June’03 – draft-ietf-tsvwg-tcp-frto-00, Oct ’03) • More compact algorithm description • Made SACK-version simpler • Not usable when loss recovery underway • Discussion on this case in Appendix • Added SCTP considerations section • Issues with multi-homed association • Issues with chunk bundling • Clarified examples

  4. Changes from tsvwg-00 to tsvwg-01(draft-ietf-tsvwg-tcp-frto-00 Oct’03 – draft-ietf-tsvwg-tcp-frto-01, Feb’04) • Editorial changes to improve readability • Modified discussion on responding to spurious timeout

  5. Next Steps • tcpm milestone: submit to IESG for publication as Experimental (Mar/May’04)(?) • Submit as a tcpm draft after IETF-59 • Ready to be wrapped up? • Ready for WG last call? • Comments?

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