[tcpm] Review: draft-ietf-tcpm-fastopen-07 and sharding
Bob Briscoe <bob.briscoe@bt.com> Thu, 27 February 2014 15:32 UTC
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Date: Thu, 27 Feb 2014 15:31:58 +0000
To: Yuchung Cheng <ycheng@google.com>
From: Bob Briscoe <bob.briscoe@bt.com>
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Cc: tcpm IETF list <tcpm@ietf.org>, draft-ietf-tcpm-fastopen@tools.ietf.org
Subject: [tcpm] Review: draft-ietf-tcpm-fastopen-07 and sharding
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Yuchung & co-authors, Thx for the new draft. * The more specific text in "6.1 Duplicate Data in SYNs" is better, thx. * I'm happy with the text about the initial congestion window too. I don't want to hold up this draft any further. However, I would prefer the IESG to see the following text about cookie-in-FIN in the draft. It raises the concern about sharding, and provides a potential solution if it becomes a problem. I've also added some nits, that could be dealt with at the same time. 4.2.1 OLD: An alternate proposal is to request cookie in FIN instead since FIN- drop by incompatible middle-box does not affect latency. However such paths are likely to drop SYN packet with data later, and many applications close the connections with RST instead, so the actual benefit of this approach is not clear. SUGGESTED: An alternate proposal is to request a TFO cookie in the FIN instead, since FIN-drop by incompatible middle-boxes does not affect latency. However paths that block SYN cookies may be more likely to drop a later SYN packet with data, and many applications close a connection with RST instead anyway. Although cookie-in-FIN may not improve robustness, it would give clients using a single connection a latency advantage over clients opening multiple parallel connections. If experiments with TFO find that it leads to increased connection-sharding, cookie-in-FIN may prove to be a useful alternative. REASONING: * The previous dismissal of cookie in FIN said what these boxes were likely to do, but gave no evidence, so I've made it more circumspect. * When I originally proposed cookie in FIN, I gave two reasons for it, but the main one seemed to get overlooked - the advantage that TFO in SYN gives to sharding clients. * I also improved the English. NITS ==== Section 4.2.2 OLD: 6. Advance to the SYN-RCVD state. If the FastOpened flag is set, the server MUST follow the congestion control [RFC5681] to set the initial congestion window [RFC3390], to send more data packets. SUGGESTED: 6. Advance to the SYN-RCVD state. If the FastOpened flag is set, the server MUST follow RFC 5681 (based on RFC 3390) to set the initial congestion window for sending more data packets. Section 6.3.3 s/idem-potency/idempotency/ Section 7.3 s/Further experimentation regarding the congestion control impact are useful./ /Further experimentation regarding the congestion control impact will be useful./ Section 8.3 s/Therefore applications like Web may not receive the latency benefit as TFO./ /Therefore the latency of applications such as Web may be worse than with TFO./ Bob ________________________________________________________________ Bob Briscoe, BT