blob: ed969534bc66274a11635902a8e6c6284de5a9d8 [file] [log] [blame]
// 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 "quic/core/congestion_control/prr_sender.h"
#include "quic/core/quic_packets.h"
namespace quic {
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 prior_in_flight) {
bytes_sent_since_loss_ = 0;
bytes_in_flight_before_loss_ = prior_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_;
}
bool PrrSender::CanSend(QuicByteCount congestion_window,
QuicByteCount bytes_in_flight,
QuicByteCount slowstart_threshold) const {
// Return QuicTime::Zero in order to ensure limited transmit always works.
if (bytes_sent_since_loss_ == 0 || bytes_in_flight < kMaxSegmentSize) {
return true;
}
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 false;
}
return true;
}
// 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 true;
}
return false;
}
} // namespace quic