[quicwg/base-drafts] Simplify TLP and RTO into Probe Timeout (#2114)

janaiyengar <notifications@github.com> Tue, 11 December 2018 15:57 UTC

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Date: Tue, 11 Dec 2018 15:57:24 +0000
From: janaiyengar <notifications@github.com>
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Subject: [quicwg/base-drafts] Simplify TLP and RTO into Probe Timeout (#2114)
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This PR simplifies QUIC's timeout-based loss detection mechanisms. Unfortunately, this PR cuts through text is many places, so I'm summarizing the key changes here.  The compiled version of the draft, [here](https://quicwg.org/base-drafts/pto/draft-ietf-quic-recovery.html), might be easier to read than the diffs.

- TLP and RTO are combined into a single "Probe Timeout" (PTO). Consecutive PTOs are exponentially longer, just like RTO used to be.  The rationale for calling this a "Probe" Timeout is that loss detection in QUIC only happens when an ack is received, and this timer and timeout only cause probe packets to be sent out to elicit acks.

- Min TLP, RTO, crypto timeout values are now removed. We had a minTLP of 10ms (which was used as a min for the crypto timeout as well) and a minRTO of 200ms.  The number of 10ms was a bit arbitrary, and based on a long-expired TCP TLP individual draft. We discussed the minRTO in #1017, and there was general agreement that adding a max_ack_delay should allow us to remove the minRTO. max_ack_delay is now present and included in the PTO computation.

- Clock granularity is added for both crypto and PTO timeouts, ensuring that even when the computed network RTT might be too small and represented as 0, timeouts are set for at least 1 clock tick. This is in keeping with use of granularity in TCP (RFC 6298). A min granularity of 1ms is recommended.
You can view, comment on, or merge this pull request online at:


-- Commit Summary --

  * sync
  * first cut of mechanism
  * complete text
  * pseudocode changes

-- File Changes --

    M draft-ietf-quic-recovery.md (251)

-- Patch Links --


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