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/*
* Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
// A convenience class to store RTT samples and calculate smoothed RTT.
// From the Quic BBR implementation in Chromium.
#ifndef MODULES_CONGESTION_CONTROLLER_BBR_RTT_STATS_H_
#define MODULES_CONGESTION_CONTROLLER_BBR_RTT_STATS_H_
#include "api/units/time_delta.h"
#include "api/units/timestamp.h"
#include "rtc_base/checks.h"
#include "rtc_base/constructormagic.h"
#include "rtc_base/logging.h"
namespace webrtc {
namespace bbr {
class RttStats {
public:
RttStats();
// Updates the RTT from an incoming ack which is received |send_delta| after
// the packet is sent and the peer reports the ack being delayed |ack_delay|.
void UpdateRtt(TimeDelta send_delta, TimeDelta ack_delay, Timestamp now);
// Causes the smoothed_rtt to be increased to the latest_rtt if the latest_rtt
// is larger. The mean deviation is increased to the most recent deviation if
// it's larger.
void ExpireSmoothedMetrics();
// Called when connection migrates and RTT measurement needs to be reset.
void OnConnectionMigration();
// Returns the EWMA smoothed RTT for the connection.
// May return Zero if no valid updates have occurred.
TimeDelta smoothed_rtt() const { return smoothed_rtt_; }
// Returns the EWMA smoothed RTT prior to the most recent RTT sample.
TimeDelta previous_srtt() const { return previous_srtt_; }
int64_t initial_rtt_us() const { return initial_rtt_us_; }
// Sets an initial RTT to be used for SmoothedRtt before any RTT updates.
void set_initial_rtt_us(int64_t initial_rtt_us) {
RTC_DCHECK_GE(initial_rtt_us, 0);
if (initial_rtt_us <= 0) {
RTC_LOG(LS_ERROR) << "Attempt to set initial rtt to <= 0.";
return;
}
initial_rtt_us_ = initial_rtt_us;
}
// The most recent RTT measurement.
// May return Zero if no valid updates have occurred.
TimeDelta latest_rtt() const { return latest_rtt_; }
// Returns the min_rtt for the entire connection.
// May return Zero if no valid updates have occurred.
TimeDelta min_rtt() const { return min_rtt_; }
TimeDelta mean_deviation() const { return mean_deviation_; }
private:
TimeDelta latest_rtt_;
TimeDelta min_rtt_;
TimeDelta smoothed_rtt_;
TimeDelta previous_srtt_;
// Mean RTT deviation during this session.
// Approximation of standard deviation, the error is roughly 1.25 times
// larger than the standard deviation, for a normally distributed signal.
TimeDelta mean_deviation_;
int64_t initial_rtt_us_;
RTC_DISALLOW_COPY_AND_ASSIGN(RttStats);
};
} // namespace bbr
} // namespace webrtc
#endif // MODULES_CONGESTION_CONTROLLER_BBR_RTT_STATS_H_