Re: [quicwg/base-drafts] Add more context and text around ACK frequency (#3706)

Martin Thomson <notifications@github.com> Thu, 28 May 2020 23:53 UTC

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Date: Thu, 28 May 2020 16:53:30 -0700
From: Martin Thomson <notifications@github.com>
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Subject: Re: [quicwg/base-drafts] Add more context and text around ACK frequency (#3706)
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@martinthomson approved this pull request.

Thanks!  This appears to be much better.  And it points in the right direction without being overly prescriptive.

>  
-Packets containing only ACK frames are not congestion controlled, so there are
-limits on how frequently they can be sent.  An endpoint MUST NOT send more than
-one ACK-frame-only packet in response to receiving an ack-eliciting packet.  An
-endpoint MUST NOT send a non-ack-eliciting packet in response to a
-non-ack-eliciting packet, even if there are packet gaps which precede the
-received packet. Limiting ACK frames avoids an infinite feedback loop of
-acknowledgements, which could prevent the connection from ever becoming idle.
-However, the endpoint acknowledges non-ACK-eliciting packets when it sends an
-ACK frame.
+### Acknowledgement Frequency
+
+A receiver determines how frequently to send acknowledgements in response to
+ack-eliciting packets. This determination involves a tradeoff however.

```suggestion
ack-eliciting packets. This determination involves a tradeoff.
```

>  
-Packets containing only ACK frames are not congestion controlled, so there are
-limits on how frequently they can be sent.  An endpoint MUST NOT send more than
-one ACK-frame-only packet in response to receiving an ack-eliciting packet.  An
-endpoint MUST NOT send a non-ack-eliciting packet in response to a
-non-ack-eliciting packet, even if there are packet gaps which precede the
-received packet. Limiting ACK frames avoids an infinite feedback loop of
-acknowledgements, which could prevent the connection from ever becoming idle.
-However, the endpoint acknowledges non-ACK-eliciting packets when it sends an
-ACK frame.
+### Acknowledgement Frequency
+
+A receiver determines how frequently to send acknowledgements in response to
+ack-eliciting packets. This determination involves a tradeoff however.
+
+Endpoints rely on timely acknowledgment to detect loss; see Section X of

We'll need a value for X.

```suggestion
Endpoints rely on timely acknowledgment to detect loss; see Section 5 of
```

> -limits on how frequently they can be sent.  An endpoint MUST NOT send more than
-one ACK-frame-only packet in response to receiving an ack-eliciting packet.  An
-endpoint MUST NOT send a non-ack-eliciting packet in response to a
-non-ack-eliciting packet, even if there are packet gaps which precede the
-received packet. Limiting ACK frames avoids an infinite feedback loop of
-acknowledgements, which could prevent the connection from ever becoming idle.
-However, the endpoint acknowledges non-ACK-eliciting packets when it sends an
-ACK frame.
+### Acknowledgement Frequency
+
+A receiver determines how frequently to send acknowledgements in response to
+ack-eliciting packets. This determination involves a tradeoff however.
+
+Endpoints rely on timely acknowledgment to detect loss; see Section X of
+{{QUIC-RECOVERY}}. Window-based congestion controllers, such as the one in
+Section X of {{QUIC-RECOVERY}}, rely on acknowledgments to manage their sending

```suggestion
Section 6 of {{QUIC-RECOVERY}}, rely on acknowledgments to manage their sending
```

> +packets. Better knowledge of network conditions or further research and
+experimentation might suggest alternative acknowledgment strategies with better
+performance characteristics. This recommendation is general in nature and
+consistent with recommendations for TCP endpoint behavior {{?RFC5681}}.

I think maybe we can swap the last two sentences, so that "this recommendation" is better bound to the first sentence.

> @@ -3555,6 +3563,16 @@ messages are delayed or lost.  Note that the same limitation applies to other
 data sent by the server protected by the 1-RTT keys.
 
 
+### PADDING Frames Consume Congestion Window
+
+Packets containing PADDING frames are considered to be in flight for congestion
+control purposes {{QUIC-RECOVERY}}. Sending only PADDING frames might cause the
+sender to become limited by the congestion controller with no acknowledgments
+forthcoming from the receiver. Therefore, a sender SHOULD ensure that other
+frames are sent periodically in addition to PADDING frames to elicit acknowledgments from

Check line length.

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