// receiver calls OnRead every time a packet is received
// OnRead returns true, if the roundtrip estimate has changed
func (t *receiverRoundtripEstimator) OnRead(ff *dccp.FeedforwardHeader) bool {
// Read RoundtripReportOption
// Currently RoundtripReportOption is allowed on any packet type
var report *RoundtripReportOption
for _, opt := range ff.Options {
if report = DecodeRoundtripReportOption(opt); report != nil {
break
}
}
if report == nil {
t.amb.E(dccp.EventWarn, "Missing roundtrip report opt", ff)
return false
}
// Sanity checks
rtt := dccp.NanoFromTenMicro(report.Roundtrip)
if rtt <= 0 || rtt > 30e9 {
t.amb.E(dccp.EventWarn, "Invalid roundtrip report opt", ff)
return false
}
// Update RTT estimate
t.rtt, t.rttTime = rtt, ff.Time
t.amb.E(dccp.EventMatch, fmt.Sprintf("Report —> RTT=%s", dccp.Nstoa(t.rtt)), ff,
RoundtripSample(RoundtripReportSample, t.rtt), RoundtripReportCheckpoint)
return true
}
// Sender calls OnRead for every arriving Ack packet.
// OnRead returns true if the RTT estimate has changed.
func (t *senderRoundtripEstimator) OnRead(fb *dccp.FeedbackHeader) bool {
// Read ElapsedTimeOption
if fb.Type != dccp.Ack && fb.Type != dccp.DataAck {
return false
}
var elapsed *dccp.ElapsedTimeOption
for _, opt := range fb.Options {
if elapsed = dccp.DecodeElapsedTimeOption(opt); elapsed != nil {
break
}
}
if elapsed == nil {
t.amb.E(dccp.EventWarn, "Missing elapsed opt", fb)
return false
}
// Update RTT estimate
s := t.find(fb.AckNo)
if s == nil {
return false
}
elapsedNS := dccp.NanoFromTenMicro(elapsed.Elapsed) // Elapsed time at receiver in nanoseconds
if elapsedNS < 0 {
t.amb.E(dccp.EventWarn, "Invalid elapsed opt", fb)
return false
}
est := (fb.Time - s.Time - elapsedNS)
if est <= 0 {
t.amb.E(dccp.EventWarn, "Invalid elapsed opt", fb)
return false
}
est_old := t.estimate
if est_old == 0 {
t.estimate = est
} else {
t.estimate = (est*SenderRoundtripWeightNew + est_old*SenderRoundtripWeightOld) /
(SenderRoundtripWeightNew + SenderRoundtripWeightOld)
}
t.amb.E(dccp.EventMatch, fmt.Sprintf("Elapsed —> RTT=%s", dccp.Nstoa(t.estimate)), fb,
RoundtripSample(RoundtripElapsedSample, t.estimate), RoundtripElapsedCheckpoint)
return true
}