64 lines
2.2 KiB
Go
64 lines
2.2 KiB
Go
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package congestion
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import (
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"time"
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"github.com/lucas-clemente/quic-go/protocol"
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"github.com/lucas-clemente/quic-go/utils"
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)
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// PrrSender implements the Proportional Rate Reduction (PRR) per RFC 6937
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type PrrSender struct {
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bytesSentSinceLoss protocol.ByteCount
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bytesDeliveredSinceLoss protocol.ByteCount
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ackCountSinceLoss protocol.ByteCount
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bytesInFlightBeforeLoss protocol.ByteCount
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}
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// OnPacketSent should be called after a packet was sent
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func (p *PrrSender) OnPacketSent(sentBytes protocol.ByteCount) {
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p.bytesSentSinceLoss += sentBytes
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}
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// OnPacketLost should be called on the first loss that triggers a recovery
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// period and all other methods in this class should only be called when in
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// recovery.
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func (p *PrrSender) OnPacketLost(bytesInFlight protocol.ByteCount) {
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p.bytesSentSinceLoss = 0
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p.bytesInFlightBeforeLoss = bytesInFlight
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p.bytesDeliveredSinceLoss = 0
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p.ackCountSinceLoss = 0
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}
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// OnPacketAcked should be called after a packet was acked
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func (p *PrrSender) OnPacketAcked(ackedBytes protocol.ByteCount) {
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p.bytesDeliveredSinceLoss += ackedBytes
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p.ackCountSinceLoss++
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}
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// TimeUntilSend calculates the time until a packet can be sent
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func (p *PrrSender) TimeUntilSend(congestionWindow, bytesInFlight, slowstartThreshold protocol.ByteCount) time.Duration {
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// Return QuicTime::Zero In order to ensure limited transmit always works.
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if p.bytesSentSinceLoss == 0 || bytesInFlight < protocol.DefaultTCPMSS {
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return 0
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}
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if congestionWindow > bytesInFlight {
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// During PRR-SSRB, limit outgoing packets to 1 extra MSS per ack, instead
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// of sending the entire available window. This prevents burst retransmits
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// when more packets are lost than the CWND reduction.
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// limit = MAX(prr_delivered - prr_out, DeliveredData) + MSS
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if p.bytesDeliveredSinceLoss+p.ackCountSinceLoss*protocol.DefaultTCPMSS <= p.bytesSentSinceLoss {
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return utils.InfDuration
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}
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return 0
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}
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// Implement Proportional Rate Reduction (RFC6937).
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// Checks a simplified version of the PRR formula that doesn't use division:
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// AvailableSendWindow =
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// CEIL(prr_delivered * ssthresh / BytesInFlightAtLoss) - prr_sent
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if p.bytesDeliveredSinceLoss*slowstartThreshold > p.bytesSentSinceLoss*p.bytesInFlightBeforeLoss {
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return 0
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}
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return utils.InfDuration
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}
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