Re: [multipathtcp] Options or Payload?

Joe Touch <touch@ISI.EDU> Tue, 10 November 2009 01:55 UTC

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Date: Mon, 09 Nov 2009 17:54:33 -0800
From: Joe Touch <touch@ISI.EDU>
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To: Yoshifumi Nishida <nishida@sfc.wide.ad.jp>
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Subject: Re: [multipathtcp] Options or Payload?
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This has been tried in various places in TCP to extend the options
space. It'd be useful to take a look at that work as context.

Joe

Yoshifumi Nishida wrote:
> Hello,
> How about having a simple option which indicates the offset for real tcp payload?
> For example, if mptcp packets conveys 10 bytes control info in the payload, set 
> offset to 10 in the option.
> 
> Thanks,
> --
> Yoshifumi Nishida
> nishida@sfc.wide.ad.jp
> 
> From: "Ford, Alan" <alan.ford@roke.co.uk>
> Subject: [multipathtcp] Options or Payload?
> Date: Tue, 10 Nov 2009 00:58:48 -0000
> Message-ID: <2181C5F19DD0254692452BFF3EAF1D6808D7BB51@rsys005a.comm.ad.roke.co.uk>
> 
>  > Hi all,
>  > 
>  > One of the big issues to be raised during yesterday's MPTCP session was
>  > the question of whether TCP Options are really the right place to be
>  > doing this. This is not the first time this has come up but deserves
>  > further exploration.
>  > 
>  > Specifically, instead of doing this with TCP Options, the same
>  > instructions could be included in the payload. Similar to TLS, the data
>  > could be chunked and each chunk has a data sequence and length header.
>  > These can be interspersed with control blocks to signal addresses,
>  > security of joining subflows to connections, and connection close. A
>  > simple 2-octet TCP option would still be used in the initial SYN to
>  > signal MPTCP capability.
>  > 
>  > This has the benefit that it would allow the signalling to have
>  > reliability, and we wouldn't be hit with option space limits, and thus
>  > be potentially able to do better security algorithms. It would also give
>  > us greater freedom in signals for future extensibility (for example, if
>  > we wanted to signal ports for additional subflows, not just addresses).
>  > 
>  > On the downside, there may be cases where this could confuse
>  > middleboxes, e.g. expecting HTTP on port 80 and finding this kind of
>  > data instead. However, since a TCP option would be used at the start to
>  > identify capability, if this were dropped by a middlebox/proxy then
>  > MPTCP would not be used.
>  > 
>  > What do people think is the best approach?
>  > 
>  > Regards,
>  > Alan
>  > 
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