Re: [quicwg/base-drafts] PTO MUST send new data or retransmit data if possible (#3057)

[martinduke <[e-mail]>]

martinduke commented on this pull request.



>  
-When there is no data to send, the sender SHOULD send a PING or other
-ack-eliciting frame in a single packet, re-arming the PTO timer.
+It is possible the sender has no new or previously-sent data to send.
+As an example, consider the following sequence of events: new application data
+is sent in a STREAM frame, deemed lost, then retransmitted in a new packet,
+and then the original transmission is acknowledged.  When there is no data to
+send, the sender SHOULD send a PING or other ack-eliciting frame in a single
+packet, re-arming the PTO timer.

What is the purpose of this statement?

> Data that was previously sent with Initial encryption
> MUST be sent before Handshake data and data previously sent at Handshake
> MUST be sent before any ApplicationData data.

Doesn't this conflict with the "PTO per packet number space" PR? If I'm implementing that PR most literally, I should PTO only the data from the space that expired. For example, I can have the 0RTT/1RTT PTO timer running first with some handshake data also in flight, and I should send just 0RTT/1RTT.

If I'm coalescing, I'm not sure why this would matter.

As for "MUST send new/unacked data", is that necessary? Why is not OK to send a PING instead to reduce bytes in flight? Perhaps I'm expecting new data soon and want to preserve the window space? I'd prefer if this were a SHOULD.

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