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Advancing RFC 4138 < draft-ietf-tcpm-rfc4138bis-01 > < draft-kojo-tcpm-frto-eval-01 >

Advancing RFC 4138 < draft-ietf-tcpm-rfc4138bis-01 > < draft-kojo-tcpm-frto-eval-01 >. Pasi Sarolahti Markku Kojo Kazunori Yamamoto Max Hata IETF-70 / TCPM / Vancouver, BC, Canada / December 4 th 2007. Problems with regular TCP. On Spurious Timeouts

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Advancing RFC 4138 < draft-ietf-tcpm-rfc4138bis-01 > < draft-kojo-tcpm-frto-eval-01 >

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  1. 1 Advancing RFC 4138<draft-ietf-tcpm-rfc4138bis-01><draft-kojo-tcpm-frto-eval-01> Pasi Sarolahti Markku Kojo Kazunori Yamamoto Max Hata IETF-70 / TCPM / Vancouver, BC, Canada / December 4th 2007

  2. 2 Problems with regular TCP • On Spurious Timeouts • Regular TCP sender retransmits whole window unnecessarily in slow start • Network resources are wasted • In many cases severe performance penalty to the TCP flow • Dishonors packet conservation principle

  3. 3 F-RTO: Detecting Spurious RTOs • F-RTO slightly modifies TCP sender behavior • After RTO retransmission try to send a couple of new segments • If new acknowledgements for non-retransmitted segments flow in, assume RTO was spurious • Otherwise new segments trigger DupACKs, and sender should assume genuine RTO • No TCP options required • Compatible with existing TCP implementations • Does not cause network congestion • Might not detect spurious timeout in some cases • If F-RTO does not detect spurious RTO, it reverts back to traditional RTO recovery

  4. 4 Current Progress • Revised RFC 4138 targeting at PS <draft-ietf-tcpm-rfc4138bis-01> • Changes from -00: • Added back the original SACK-algorithm from RFC 4138 after the common feedback to have the SACK-algorithm in the document • Clarified behavior on multiple timeouts • Clarified that ACKs that do not acknowledge new data but are not duplicate acknowledgements are ignored • Other small clarifications on both algorithms and general editing • Added one paragraph describing the basic idea of the SACK algorithm

  5. 5 Current Progress (cont’d) • Wrote I-D"Evaluation of RFC 4138" <draft-kojo-tcpm-frto-eval-01.txt> • Points out the problems with regular RTO recovery and usefulness of F-RTO • Evaluates F-RTO to show it is not harmful to the network, corner cases included • Summarizes experimentation results • Changes from -eval-00: • Added a summary on experimentation with malicious receiver • receiver does not benefit from cheating when conservative response is used • receiver may benefit when aggressive response is used • General editing

  6. 6 Ready to advance? • A number of known F-RTO implementations are out there • Proposals and support to advance to PS have been expressed several times by implementors • Experimentations have been carried with several implementations showing positive results • All feedback has been positive • Implementors: straightforward to implement no issues with the spec • Many implementations enable F-RTO by default • Windows Vista • Microsoft report at IETF-68 about their positive experiences • Linux • SACK-enhanced F-RTO enabled by default from up-coming release of 2.6.24 and onward, and falls back to basic variant if SACK not negotiated

  7. 7 Next Steps • Basically ready for WGLC • First need green light from WG for advancing to PS

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