Re: [quicwg/base-drafts] use a HANDSHAKE_DONE frame to drive the handshake to confirmation (#3145)

[Kazuho Oku <[e-mail]>]

kazuho commented on this pull request.



> @@ -760,14 +756,9 @@ and ignoring any outstanding Initial packets.
 
 ### Discarding Handshake Keys
 
-An endpoint MUST NOT discard its handshake keys until the TLS handshake is
-confirmed ({{handshake-confirmed}}).  An endpoint SHOULD discard its handshake
-keys as soon as it has confirmed the handshake.  Most application protocols
-will send data after the handshake, resulting in acknowledgements that allow
-both endpoints to discard their handshake keys promptly.  Endpoints that do
-not have reason to send immediately after completing the handshake MAY send
-ack-eliciting frames, such as PING, which will cause the handshake to be
-confirmed when they are acknowledged.
+An endpoint MUST discard its handshake keys when the TLS handshake is confirmed
+({{handshake-confirmed}}).  The server MUST send a HANDSHAKE_DONE frame within
+one round-trip time of handshake completion.

@ianswett 
> If the server is sending HANDSHAKE_DONE, isn't it no longer 0.5RTT data?

Yes. This is 1 RTT, *not* 0.5 RTT.

Regarding when HANDSHAKE_DONE should be sent, my view is that it HANDSHAKE_DONE is essentially an ACK for the Handshake packet. Based on that view, I do not see a reason why it should be sent at a different timing than other acks for Handshake packets (i.e. send immediately, though an endpoint might wait for a short amount of time to bundle ACK with some other data).

In practice, there is no reason to delay the emission of HANDSHAKE_DONE as much as 1 RTT in HTTP/3. The server should be sending HANDSHAKE_DONE at an early moment for letting the client know that the handshake is done before the client retransmits CF, doing so has a higher probability of having CWND increased at an earlier point. 

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