Re: [quicwg/base-drafts] Limit ack_delay by max_ack_delay (#2099)

janaiyengar <notifications@github.com> Fri, 07 December 2018 00:55 UTC

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Subject: Re: [quicwg/base-drafts] Limit ack_delay by max_ack_delay (#2099)
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janaiyengar commented on this pull request.



> @@ -267,6 +267,26 @@ all subsequent ACK frames containing them could be lost. In this case, the
 loss recovery algorithm may cause spurious retransmits, but the sender will
 continue making forward progress.
 
+# Computing the RTT estimate
+
+RTT is calculated when an ACK frame arrives by computing the difference between
+the current time and the time the largest acked packet was sent.  If the
+largest acked packet is not newly acknowledged, RTT cannot be calculated.
+
+When RTT is calculated, the ack delay field from the ACK frame SHOULD be limited
+to the max_ack_delay specified by the peer.  Limiting ack_delay to max_ack_delay
+ensures a peer specifying an extremely small max_ack_delay doesn't cause more
+spurious timeouts than a peer that correctly specifies max_ack_delay. It SHOULD
+be subtracted from the RTT as long as the result is larger than the Min RTT.

s/Min RTT/min_rtt

> @@ -267,6 +267,26 @@ all subsequent ACK frames containing them could be lost. In this case, the
 loss recovery algorithm may cause spurious retransmits, but the sender will
 continue making forward progress.
 
+# Computing the RTT estimate
+
+RTT is calculated when an ACK frame arrives by computing the difference between
+the current time and the time the largest acked packet was sent.  If the
+largest acked packet is not newly acknowledged, RTT cannot be calculated.
+
+When RTT is calculated, the ack delay field from the ACK frame SHOULD be limited
+to the max_ack_delay specified by the peer.  Limiting ack_delay to max_ack_delay
+ensures a peer specifying an extremely small max_ack_delay doesn't cause more
+spurious timeouts than a peer that correctly specifies max_ack_delay. It SHOULD
+be subtracted from the RTT as long as the result is larger than the Min RTT.
+If the result is smaller than the min_rtt, the RTT should be used, but the
+ack delay field should be ignored.

I wouldn't add this in before we resolve #2060.

> +RTT is calculated when an ACK frame arrives by computing the difference between
+the current time and the time the largest acked packet was sent.  If the
+largest acked packet is not newly acknowledged, RTT cannot be calculated.
+
+When RTT is calculated, the ack delay field from the ACK frame SHOULD be limited
+to the max_ack_delay specified by the peer.  Limiting ack_delay to max_ack_delay
+ensures a peer specifying an extremely small max_ack_delay doesn't cause more
+spurious timeouts than a peer that correctly specifies max_ack_delay. It SHOULD
+be subtracted from the RTT as long as the result is larger than the Min RTT.
+If the result is smaller than the min_rtt, the RTT should be used, but the
+ack delay field should be ignored.
+
+Like TCP, QUIC calculates both smoothed RTT and RTT variance similar to those
+specified in {{?RFC6298}}.
+
+Min RTT is the minimum RTT measured over the connection, prior to adjusting by

s/Min RTT/min_rtt

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