Send SACK-IMMEDIATELY before CWND full#739
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SACK-IMMEDIATELY was introduced in RFC-7053 to improve performance in various situations. While usrsctp support the SACK-IMMEDIATELY, it does not implement the case where SACK-IMMEDIATELY should be sent on last packet before hitting the congestion window limit. Setting the SACK-IMMEDIATELY flag on the last packet before the congestion window is full is crucial for the performance on high latency links. Pion has made a similar patch, see reasoning and meassures here: pion/sctp#62. I have came to similiar conclusions in my speed tests. This patch tries to detect last packet in congestion window without too much code refactoring. There is a risk that too many packets gets the SACK-IMMEDIATELY flag (if the packets are much smaller than 1 MTU), but the only drawback of that, as far as I can tell, is potentially some extra SACKs sent by the receiver.
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SACK-IMMEDIATELY was introduced in RFC-7053 to improve performance in various situations. While usrsctp support the SACK-IMMEDIATELY, it does not implement the case where SACK-IMMEDIATELY should be sent on last packet before hitting the congestion window limit.
Setting the SACK-IMMEDIATELY flag on the last packet before the congestion window is full is crucial for the performance on high latency links. Pion has made a similar patch, see reasoning and meassures here: pion/sctp#62. I have came to similiar conclusions in my speed tests.
This patch tries to detect last packet in congestion window without too much code refactoring. There is a risk that too many packets gets the SACK-IMMEDIATELY flag (if the packets are much smaller than 1 MTU), but the only drawback of that, as far as I can tell, is potentially some extra SACKs sent by the receiver.