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Don't update RTT for ack-only packets #984

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Don't update RTT for ack-only packets #984

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28baaa0
Don't update RTT for ack-only packets
martinthomson Dec 5, 2017
81e0bba
Make normative, clearer
martinthomson Dec 5, 2017
2651b66
Use the as-yet-undefined is_ackable()
martinthomson Dec 5, 2017
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14 changes: 11 additions & 3 deletions draft-ietf-quic-recovery.md
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Expand Up @@ -577,15 +577,23 @@ Pseudocode for OnPacketSent follows:

### On Ack Receipt

When an ack is received, it may acknowledge 0 or more packets.
When an acknowledgment is received, it may acknowledge 0 or more packets.

The first acknowledgment received for the largest acknowledged packet is used to
update the estimate of minimum and smoothed RTT. However, if the largest
acknowledged packet would not have caused an acknowledgment to be sent, RTT
estimates MUST NOT be updated, because the acknowledgment could be significantly
delayed.

Pseudocode for OnAckReceived and UpdateRtt follow:

~~~
OnAckReceived(ack):
largest_acked_packet = ack.largest_acked
// If the largest acked is newly acked, update the RTT.
if (sent_packets[ack.largest_acked]):
// If the largest acked is newly acked and is a packet
// that would normally cause an ack, update the RTT.
if (sent_packets[ack.largest_acked] and
is_ackable(sent_packets[ack.largest_acked])):
latest_rtt = now - sent_packets[ack.largest_acked].time
UpdateRtt(latest_rtt, ack.ack_delay)
// Find all newly acked packets.
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