Re: [quicwg/base-drafts] Merge Crypto timeout and PTO (#2806)

ianswett <> Sat, 13 July 2019 11:23 UTC

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Subject: Re: [quicwg/base-drafts] Merge Crypto timeout and PTO (#2806)
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ianswett commented on this pull request.

Thanks Ryan, I took your editorial suggestion, I can file an issue for the last comment.

>  ## Probe Timeout {#pto}
-A Probe Timeout (PTO) triggers a probe packet when ack-eliciting data is in
-flight but an acknowledgement is not received within the expected period of
-time.  A PTO enables a connection to recover from loss of tail packets or acks.
-The PTO algorithm used in QUIC implements the reliability functions of Tail Loss
-Probe {{?TLP=I-D.dukkipati-tcpm-tcp-loss-probe}} {{?RACK}}, RTO {{?RFC5681}} and
+A Probe Timeout (PTO) triggers sending one or two probe packets when

It's 1 or 2 because some impls only do 1 packet PTO(TLP).  I could recommend two packets during the handshake, in order to speed handshake completion?

It actually should be datagrams, but I'm inclined to change that in a follow-up, rather that burying it in this change?

> +data.  If no data can be sent, then the PTO alarm MUST NOT be armed until
+data has been received from the client.
+Because the server could be blocked until more packets are received, the client
+MUST ensure that the retransmission timer is set if the client does not yet
+have 1-RTT keys.  If the probe timer expires before the client has 1-RTT keys,
+it is possible that the client may not have any crypto data to retransmit.
+However, the client MUST send a new packet, containing only PADDING frames if
+necessary, to allow the server to continue sending data. If Handshake keys
+are available to the client, it MUST send a Handshake packet, and otherwise
+it MUST send an Initial packet in a UDP datagram of at least 1200 bytes.
+Because Initial packets only containing PADDING do not elicit an
+acknowledgement, they may never be acknowledged, but they are removed from
+bytes in flight when the client gets Handshake keys and the Initial keys are

True, we recommend that elsewhere.  I think we should change that in a follow-up though, since it's not directly related to this change?

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