[quicwg/base-drafts] Recovery: when PTO expires and no data to send (#3286)

Junho Choi <notifications@github.com> Thu, 05 December 2019 22:00 UTC

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Date: Thu, 05 Dec 2019 14:00:46 -0800
From: Junho Choi <notifications@github.com>
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Subject: [quicwg/base-drafts] Recovery: when PTO expires and no data to send (#3286)
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OnLossDetectionTimeout() pseudo code says:

```
   // PTO. Send new data if available, else retransmit old data.
    // If neither is available, send a single PING frame.
```

And "Sending Probe Packets" says:

> When a PTO timer expires, a sender MUST send at least one ack-eliciting packet in the packet number space as a probe, unless there is no data available to send
...
> 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.

For me it's a little wasteful to keep sending an ack-eliciting frame (including PING) as a Probe packet when there is no data to send. In this case if the client become unresponsive before receiving PING, the server may keep sending PING as a Probe packet until idle timeout expires in this case.

I think it's better to update as follows:

"When there is no data to send and *last Probe packet included an application data*, the sender SHOULD send a PING or other ack-eliciting frame in a single packet, re-arming the PTO timer."

It will make sure that PING as a Probe packet is sent once when the server has no further data to send.


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