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// Copyright (c) 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "net/quic/congestion_control/prr_sender.h"
#include "net/quic/quic_protocol.h"
namespace net {
namespace {
// Constant based on TCP defaults.
const QuicByteCount kMaxSegmentSize = kDefaultTCPMSS;
} // namespace
PrrSender::PrrSender()
: bytes_sent_since_loss_(0),
bytes_delivered_since_loss_(0),
ack_count_since_loss_(0),
bytes_in_flight_before_loss_(0) {}
void PrrSender::OnPacketSent(QuicByteCount sent_bytes) {
bytes_sent_since_loss_ += sent_bytes;
}
void PrrSender::OnPacketLost(QuicByteCount bytes_in_flight) {
bytes_sent_since_loss_ = 0;
bytes_in_flight_before_loss_ = bytes_in_flight;
bytes_delivered_since_loss_ = 0;
ack_count_since_loss_ = 0;
}
void PrrSender::OnPacketAcked(QuicByteCount acked_bytes) {
bytes_delivered_since_loss_ += acked_bytes;
++ack_count_since_loss_;
}
QuicTime::Delta PrrSender::TimeUntilSend(
QuicByteCount congestion_window,
QuicByteCount bytes_in_flight,
QuicByteCount slowstart_threshold) const {
// if (FLAGS_?? && bytes_in_flight < congestion_window) {
// return QuicTime::Delta::Zero();
// }
// Return QuicTime::Zero In order to ensure limited transmit always works.
if (bytes_sent_since_loss_ == 0 || bytes_in_flight < kMaxSegmentSize) {
return QuicTime::Delta::Zero();
}
if (congestion_window > bytes_in_flight) {
// During PRR-SSRB, limit outgoing packets to 1 extra MSS per ack, instead
// of sending the entire available window. This prevents burst retransmits
// when more packets are lost than the CWND reduction.
// limit = MAX(prr_delivered - prr_out, DeliveredData) + MSS
if (bytes_delivered_since_loss_ + ack_count_since_loss_ * kMaxSegmentSize <=
bytes_sent_since_loss_) {
return QuicTime::Delta::Infinite();
}
return QuicTime::Delta::Zero();
}
// Implement Proportional Rate Reduction (RFC6937).
// Checks a simplified version of the PRR formula that doesn't use division:
// AvailableSendWindow =
// CEIL(prr_delivered * ssthresh / BytesInFlightAtLoss) - prr_sent
if (bytes_delivered_since_loss_ * slowstart_threshold >
bytes_sent_since_loss_ * bytes_in_flight_before_loss_) {
return QuicTime::Delta::Zero();
}
return QuicTime::Delta::Infinite();
}
} // namespace net
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