Merge pull request #2646 from marten-seemann/max-ack-delay-initialisa…

…tion

use max_ack_delay = 0 before receving the TPs

draft-ietf-quic-recovery.md

@@ -309,7 +309,7 @@ parameter, see Section 18.1 of {{QUIC-TRANSPORT}}.  max_ack_delay implies an
 explicit contract: an endpoint promises to never delay acknowledgments of an
 ack-eliciting packet by more than the indicated value. If it does, any excess
 accrues to the RTT estimate and could result in spurious retransmissions from
-the peer.
+the peer. For Initial and Handshake packets, a max_ack_delay of 0 is used.
 
 
 # Estimating the Round-Trip Time {#compute-rtt}
@@ -1026,9 +1026,9 @@ min_rtt:
 
 max_ack_delay:
 : The maximum amount of time by which the receiver intends to delay
-  acknowledgments, in milliseconds.  The actual ack_delay in a
-  received ACK frame may be larger due to late timers, reordering,
-  or lost ACKs.
+  acknowledgments for packets in the ApplicationData packet number space. The
+  actual ack_delay in a received ACK frame may be larger due to late timers,
+  reordering, or lost ACKs.
 
 loss_time\[kPacketNumberSpace]:
 : The time at which the next packet in that packet number space will be
@@ -1052,6 +1052,7 @@ follows:
    smoothed_rtt = 0
    rttvar = 0
    min_rtt = 0
+   max_ack_delay = 0
    time_of_last_sent_ack_eliciting_packet = 0
    time_of_last_sent_crypto_packet = 0
    for pn_space in [ Initial, Handshake, ApplicationData ]:
@@ -1112,7 +1113,10 @@ OnAckReceived(ack, pn_space):
       IncludesAckEliciting(newly_acked_packets))
     latest_rtt =
       now - sent_packets[pn_space][ack.largest_acked].time_sent
-    UpdateRtt(ack.ack_delay)
+    ack_delay = 0
+    if pn_space == ApplicationData:
+      ack_delay = ack.ack_delay
+    UpdateRtt(ack_delay)
 
   // Process ECN information if present.
   if (ACK frame contains ECN information):

draft-ietf-quic-transport.md

@@ -4171,9 +4171,8 @@ ack_delay_exponent (0x000a):
 
 : The ACK delay exponent is an integer value indicating an
   exponent used to decode the ACK Delay field in the ACK frame ({{frame-ack}}).
-  If this value is absent, a default value of 3 is assumed
-  (indicating a multiplier of 8).  The default value is also used for ACK frames
-  that are sent in Initial and Handshake packets.  Values above 20 are invalid.
+  If this value is absent, a default value of 3 is assumed (indicating a
+  multiplier of 8). Values above 20 are invalid.
 
 max_ack_delay (0x000b):
 
@@ -4334,10 +4333,10 @@ ACK Delay:
   in the Largest Acknowledged field, was received by this peer.  The value of
   the ACK Delay field is scaled by multiplying the encoded value by 2 to the
   power of the value of the `ack_delay_exponent` transport parameter set by the
-  sender of the ACK frame.  The `ack_delay_exponent` defaults to 3, or a
-  multiplier of 8 (see {{transport-parameter-definitions}}).  Scaling in this
-  fashion allows for a larger range of values with a shorter encoding at the
-  cost of lower resolution.
+  sender of the ACK frame (see {{transport-parameter-definitions}}).  Scaling in
+  this fashion allows for a larger range of values with a shorter encoding at
+  the cost of lower resolution.  Because the receiver doesn't use the ACK Delay
+  for Initial and Handshake packets, a sender SHOULD send a value of 0.
 
 ACK Range Count: