Re: [quicwg/base-drafts] Send a few immediate ACKs (#2025)

[janaiyengar <[e-mail]>]

janaiyengar commented on this pull request.



>  
 Out-of-order packets SHOULD be acknowledged more quickly, in order to accelerate
 loss recovery.  The receiver SHOULD send an immediate ACK when it receives a new
-packet which is not one greater than the largest received packet number.
+packet which is not one greater than the largest received packet number.  The

Suggestion: "The receiver SHOULD send an immediate ACK when it receives a new packet which is not the next expected one.  That is, its packet number is not one greater than the largest received packet number."

>  
 Out-of-order packets SHOULD be acknowledged more quickly, in order to accelerate
 loss recovery.  The receiver SHOULD send an immediate ACK when it receives a new
-packet which is not one greater than the largest received packet number.
+packet which is not one greater than the largest received packet number.  The
+receiver MAY send an immediate ACK when a missing packet begins exceeding the
+peer's reordering threshold in packets to accelerate fast retransmit.  Time

This is a problem, since the receiver does not know the peer's reordering threshold. Also, this sentence does not make sense "a missing packet begins exceeding ... threshold in packets"

>  
 Out-of-order packets SHOULD be acknowledged more quickly, in order to accelerate
 loss recovery.  The receiver SHOULD send an immediate ACK when it receives a new
-packet which is not one greater than the largest received packet number.
+packet which is not one greater than the largest received packet number.  The
+receiver MAY send an immediate ACK when a missing packet begins exceeding the
+peer's reordering threshold in packets to accelerate fast retransmit.  Time
+threshold loss detection does not require any special ACK generation to
+accelerate fast retransmit, because it uses a timer.

I think this text should be purely prescriptive, and only from the receiver's point of view, since the sender's is basically not known at the receiver. This also does not say when a receiver should stop immediate acking, which is important IMO.

Suggested replacement for text from "The receiver MAY" : "A receiver SHOULD immediately ack at least three subsequent packets after first receiving a packet out of order, after which it SHOULD resume delaying acknowledgements."

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