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

Ryan Hamilton <notifications@github.com> Thu, 11 July 2019 16:43 UTC

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

Wow, this looks so much cleaner.

> +data it can send is limited, as specified in Section 8.1 of {{QUIC-TRANSPORT}}.
+Data at Initial encryption MUST be retransmitted before Handshake data and
+data at Handshake encryption MUST be retransmitted before any ApplicationData
+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

nit: "only containing" => "containing only"

> +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
+discarded.

Because of this, I wonder if it might make sense to include a PING along with an otherwise PADDING only packet?

>  ## 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

This is probably obvious but it doesn't seem to explicitly say what causes 1 vs 2 packet to be sent. Perhaps this is clear elsewhere? I wonder if it might make sense to say something like "two packets, if there is sufficient data available, and one otherwise". But maybe that's not really helpful.

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