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1 // Copyright (c) 2014 The Chromium Authors. All rights reserved. | |
2 // Use of this source code is governed by a BSD-style license that can be | |
3 // found in the LICENSE file. | |
4 | |
5 #include "net/quic/congestion_control/prr_sender.h" | |
6 | |
7 #include "net/quic/quic_protocol.h" | |
8 | |
9 namespace net { | |
10 | |
11 namespace { | |
12 // Constant based on TCP defaults. | |
13 const QuicByteCount kMaxSegmentSize = kDefaultTCPMSS; | |
14 } // namespace | |
15 | |
16 PrrSender::PrrSender() | |
17 : bytes_sent_since_loss_(0), | |
18 bytes_delivered_since_loss_(0), | |
19 ack_count_since_loss_(0), | |
20 bytes_in_flight_before_loss_(0) { | |
21 } | |
22 | |
23 void PrrSender::OnPacketSent(QuicByteCount sent_bytes) { | |
24 bytes_sent_since_loss_ += sent_bytes; | |
25 } | |
26 | |
27 void PrrSender::OnPacketLost(QuicByteCount bytes_in_flight) { | |
28 bytes_sent_since_loss_ = 0; | |
29 bytes_in_flight_before_loss_ = bytes_in_flight; | |
30 bytes_delivered_since_loss_ = 0; | |
31 ack_count_since_loss_ = 0; | |
32 } | |
33 | |
34 void PrrSender::OnPacketAcked(QuicByteCount acked_bytes) { | |
35 bytes_delivered_since_loss_ += acked_bytes; | |
36 ++ack_count_since_loss_; | |
37 } | |
38 | |
39 QuicTime::Delta PrrSender::TimeUntilSend( | |
40 QuicByteCount congestion_window, | |
41 QuicByteCount bytes_in_flight, | |
42 QuicPacketCount slowstart_threshold) const { | |
43 // Return QuicTime::Zero In order to ensure limited transmit always works. | |
44 if (bytes_sent_since_loss_ == 0 || bytes_in_flight < kMaxSegmentSize) { | |
45 return QuicTime::Delta::Zero(); | |
46 } | |
47 if (congestion_window > bytes_in_flight) { | |
48 // During PRR-SSRB, limit outgoing packets to 1 extra MSS per ack, instead | |
49 // of sending the entire available window. This prevents burst retransmits | |
50 // when more packets are lost than the CWND reduction. | |
51 // limit = MAX(prr_delivered - prr_out, DeliveredData) + MSS | |
52 if (bytes_delivered_since_loss_ + ack_count_since_loss_ * kMaxSegmentSize <= | |
53 bytes_sent_since_loss_) { | |
54 return QuicTime::Delta::Infinite(); | |
55 } | |
56 return QuicTime::Delta::Zero(); | |
57 } | |
58 // Implement Proportional Rate Reduction (RFC6937). | |
59 // Checks a simplified version of the PRR formula that doesn't use division: | |
60 // AvailableSendWindow = | |
61 // CEIL(prr_delivered * ssthresh / BytesInFlightAtLoss) - prr_sent | |
62 if (bytes_delivered_since_loss_ * slowstart_threshold * kMaxSegmentSize > | |
63 bytes_sent_since_loss_ * bytes_in_flight_before_loss_) { | |
64 return QuicTime::Delta::Zero(); | |
65 } | |
66 return QuicTime::Delta::Infinite(); | |
67 } | |
68 | |
69 } // namespace net | |
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