[multipathtcp] Options or Payload: pros and cons
Costin Raiciu <c.raiciu@cs.ucl.ac.uk> Wed, 11 November 2009 02:21 UTC
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From: Costin Raiciu <c.raiciu@cs.ucl.ac.uk>
Date: Wed, 11 Nov 2009 11:21:03 +0900
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Subject: [multipathtcp] Options or Payload: pros and cons
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Hi I tried to assemble a pros and cons list for the two approaches. Please add bullets to both lists until we get something reasonably exhaustive, and then we can make an informed decision. At a high level, we need to use options on every subflow at least in the syn exchange. Otherwise we can't attach the subflow to the existing connection, or can't negotiate mptcp in the first place. Ideally you'd like fate sharing: if the syn/ack exchange passes, the subflow should work. Options + nice with tcp + single subflow mptcp if friendly with IDSes, and traffic normalizers (i.e. data flow is what the app receives). - reliability is more difficult (how often do you retransmit?) drop packets? what's the failure mode when options don't get through? - boxes may crash when parsing unknown stuff. The hope is that on SYN processing is more robust with unknown options. ECN story is frightening :). Murari (Microsoft) says that even changing position of padding bits in options crashes some middleboxes; I've heard a similar story from the Linux kernel experience. However, we can't (cleanly) avoid sending options on SYNs. Payload + option space limits no longer matter; can do funkier stuff later, like negotiate keys, etc. + easier to get reliability; retransmit of control data linked to data retransmit + easier to deal with middleboxes that resegment (it just works!) + new options on syns may be allowed, but not on data (is this true)? - feels like a hack, not the traditional way to evolve tcp - implies encoding of any data sent MUST be ASCII; middleboxes (ids, traffic normalizers) that look at content and see binary stuff will probably drop the data; finally, if we used binary stuff, there is no guarantee for fate sharing. . Text encoding is less space efficient; does it matter? Any more? Costin
- [multipathtcp] Options or Payload? Ford, Alan
- Re: [multipathtcp] Options or Payload? Yoshifumi Nishida
- Re: [multipathtcp] Options or Payload? Ford, Alan
- Re: [multipathtcp] Options or Payload? Joe Touch
- Re: [multipathtcp] Options or Payload? William Herrin
- Re: [multipathtcp] Options or Payload? SCHARF, Michael
- Re: [multipathtcp] Options or Payload? Joe Touch
- [multipathtcp] Options or Payload: pros and cons Costin Raiciu
- Re: [multipathtcp] Options or Payload: pros and c… SCHARF, Michael
- Re: [multipathtcp] Options or Payload: pros and c… Costin Raiciu
- Re: [multipathtcp] Options or Payload: pros and c… Costin Raiciu