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Byte and Packet Congestion Notification draft-ietf-tsvwg-byte-pkt-congest-00.txt. Bob Briscoe , BT & UCL IETF-73 tsvwg Nov 2008. status. Byte and Packet Congestion Notification new WG draft: draft-ietf-tsvwg-byte-pkt-mark-00.txt as of 8-Aug-08

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byte and packet congestion notification draft ietf tsvwg byte pkt congest 00 txt

Byte and Packet Congestion Notificationdraft-ietf-tsvwg-byte-pkt-congest-00.txt

Bob Briscoe, BT & UCLIETF-73 tsvwg Nov 2008

status
status
  • Byte and Packet Congestion Notification
      • new WG draft: draft-ietf-tsvwg-byte-pkt-mark-00.txtas of 8-Aug-08
      • previously: draft-briscoe-tsvwg-byte-pkt-mark-02
      • intended status: informational (update to RFC2309 advice)
      • RFC publication milestone: Sep '09
      • immediate intent: encourage review
      • w-gs & r-gs affected: TSVWG, DCCP, PCN, ICCRG & PWE3
reminder exec summary
reminder (exec summary)
  • scope
      • in any AQM (e.g. RED drop, RED ECN, PCN) should we allow for packet-size when network writes or when transport reads a loss or ECN mark?
  • what little advice there is in the RFC series (RFC2309 on RED) is unclear
      • gives both options with ‘more research needed’
      • slight bias to favouring small packets, which give perverse incentives to create small packetsand seems to encourage a dangerous DoS vulnerability
  • unequivocal UPDATE to advice in RFC2309
      • AQM SHOULD NOT give smaller packets preferential treatment
      • adjust for byte-size when transport reads NOT when network writes
  • all known network layer implementations follow this advice anyway
      • retrospective tidy-up to RFC series
      • avoids complexity of catering for all possibilities, when no-one uses them
      • includes detailed advice on buffer design etc, gathered from experts & literature
  • Terminology: RED’s ‘byte mode queue measurement’ (often called just ‘byte mode’) is OK, only ‘byte mode packet drop’ deprecated
  • NOTE: don’t turn off RED completely: drop-tail is as bad or worse
why decide now between transport network
why decide now?between transport & network
  • near-impossible to design transports to meet guidelines [RFC5033]
      • if we can’t agree whether transport or network should handle packet size
  • DCCP CCID standardisation
      • hard to assess TFRC small packet variant experiment [RFC4828]
  • PCN marking algorithm standardisation [draft-ietf-pcn-marking-behaviour-01]
      • stds track draft depends on this decision
  • part of answering ICCRG question
      • what’s necessary & sufficient forwarding hardware for future cc?
      • [draft-irtf-iccrg-welzl-congestion-control-open-research-02] incorporates this I-D by ref
  • given no-one seems to have implemented network layer bias
      • advise against it before we’re stuck with an incompatible deployment fork
  • encouraging larger PMTUs by not favouring smaller ones
      • may start to solve other scaling problems
text updates draft briscoe tsvwg byte pkt mark 02 draft ietf tsvwg byte pkt congest 00
text updates[draft-briscoe-tsvwg-byte-pkt-mark-02] [draft-ietf-tsvwg-byte-pkt-congest-00]
  • few changes since previous (individual) draft
      • summarised at head of document
  • added note for RFC Editor
      • "intended to update RFC2309" (RED manifesto)
  • added question to outstanding issues section (for ICCRG)
      • will congestion of packet processing become more common?
  • updated refs (some in various w-gs have become w-g items)
reviews comments
reviews & comments
  • reviews of previous drafts
      • current draft is result of extensive previous reviews
  • current version: few comments on list since Aug
      • off-list with Iljitsch van Bejnum, Rob Hancock, Phil Eardley
        • discussion continuing – I'm trying to bring it to the tsvwg list
      • Iljitsch: wanted positive discrimination for large packets by policing small
        • I resisted: congestion notification should reflect probability of congestionno less, no more – otherwise creates unintended consequences
        • also controversy over advice IETF gives to transports
      • Phil: suggestions to make draft clearer
  • need reviews
      • signed up: Joe Touch, Wes Eddy, Jukka Manner
conclusion
conclusion
  • unequivocal UPDATE to RFC2309 (‘RED manifesto’)
    • adjust for byte-size when transport reads NOT when network writes
    • previously gave both options with ‘more research needed’
  • all known implementations follow this advice anyway
    • retrospective tidy-up to RFC series
  • reviews pending
byte and packet congestion notification draft ietf tsvwg byte pkt congest 00 txt1

Byte and Packet Congestion Notificationdraft-ietf-tsvwg-byte-pkt-congest-00.txt

Q&A