Re: [quicwg/base-drafts] Add details of marking packets lost on PTO (#2624)

ianswett <notifications@github.com> Tue, 16 April 2019 01:43 UTC

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Subject: Re: [quicwg/base-drafts] Add details of marking packets lost on PTO (#2624)
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ianswett requested changes on this pull request.

Two things.  If we want to change sender to endpoint in this draft, which I'm not a big fan of, I'd prefer to do so consistently in a single CL.  Also, the more I look at this issue, I think we have our SHOULD/MAY backwards and we SHOULD recommend always sending something, even if the only purpose is to establish loss of outstanding packets.

> @@ -592,7 +592,7 @@ TCP's retransmission timeout period {{?RFC6298}}.
 
 ### Computing PTO
 
-When an ack-eliciting packet is transmitted, the sender schedules a timer for

Can you undo the editorializing about sender/endpoint for this PR?  I prefer sender in this context, but I'd prefer to separate that question out.

>  
 ### Sending Probe Packets
 
-When a PTO timer expires, the sender MUST send one ack-eliciting packet as a
-probe, unless there is nothing to send. A sender MAY send up to two
-ack-eliciting packets, to avoid an expensive consecutive PTO expiration due
-to a single packet loss.
+When a PTO timer expires, an endpoint MUST send at least one ack-eliciting
+packet as a probe, unless there are no ack-eliciting frames to send.  An
+endpoint MAY send up to two ack-eliciting packets, to avoid an expensive
+consecutive PTO expiration due to a single packet loss.
+
+It is possible that the endpoint has no new or previously-sent data or other
+ack-eliciting frames to send.  This can happen for example when there is no new

```suggestion
ack-eliciting frames to send.  For example, this can happen when there is no new
```

>      pto_count++
+    if (any ack-eliciting frames available to send):
+      SendOneOrTwoPackets()
+    else:
+      // Mark all packets in flight as lost

This pseudocode makes an excellent argument that we should recommend sending a PING to establish loss.

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