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add some comments to help understand the RTT calculation

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Stephen Birarda 2015-07-28 14:20:51 -07:00
parent b6bdcadd33
commit e3e8219c11
1 changed files with 10 additions and 1 deletions
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11
libraries/networking/src/udt/Connection.cpp
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@ -313,7 +313,16 @@ void Connection::processNAK(std::unique_ptr<ControlPacket> controlPacket) {
}
void Connection::updateRTT(int rtt) {
// this updates the RTT using exponential weighted moving average
// This updates the RTT using exponential weighted moving average
// This is the Jacobson's forumla for RTT estimation
// http://www.mathcs.emory.edu/~cheung/Courses/455/Syllabus/7-transport/Jacobson-88.pdf
// Estimated RTT = (1 - x)(estimatedRTT) + (x)(sampleRTT)
// (where x = 0.125 via Jacobson)
// Deviation = (1 - x)(deviation) + x |sampleRTT - estimatedRTT|
// (where x = 0.25 via Jacobson)
_rttVariance = (_rttVariance * 3 + abs(rtt - _rtt)) >> 2;
_rtt = (_rtt * 7 + rtt) >> 3;
}