TCPVegasCC.h

//
//  TCPVegasCC.h
//  libraries/networking/src/udt
//
//  Created by Stephen Birarda on 2016-09-20.
//  Copyright 2016 High Fidelity, Inc.
//
//  Distributed under the Apache License, Version 2.0.
//  See the accompanying file LICENSE or http://www.apache.org/licenses/LICENSE-2.0.html
//
 
#pragma once
 
#ifndef hifi_TCPVegasCC_h
#define hifi_TCPVegasCC_h
 
#include <map>
 
#include "CongestionControl.h"
#include "Constants.h"
 
namespace udt {
    
 
class TCPVegasCC : public CongestionControl {
public:
    TCPVegasCC();
 
    virtual bool onACK(SequenceNumber ackNum, p_high_resolution_clock::time_point receiveTime) override;
    virtual void onTimeout() override {};
 
    virtual void onPacketSent(int wireSize, SequenceNumber seqNum, p_high_resolution_clock::time_point timePoint) override;
    virtual void onPacketReSent(int wireSize, SequenceNumber seqNum, p_high_resolution_clock::time_point timePoint) override;
 
    virtual int estimatedTimeout() const override;
    
protected:
    virtual void performCongestionAvoidance(SequenceNumber ack);
    virtual void setInitialSendSequenceNumber(SequenceNumber seqNum) override { _lastACK = seqNum - 1; }
private:
    bool calculateRTT(p_high_resolution_clock::time_point sendTime, p_high_resolution_clock::time_point receiveTime);
    bool needsFastRetransmit(SequenceNumber ack, bool wasDuplicateACK);
 
    bool isCongestionWindowLimited();
    void performRenoCongestionAvoidance(SequenceNumber ack);
 
    struct SentPacketData {
        SentPacketData(SequenceNumber seqNum, p_high_resolution_clock::time_point tPoint)
            : sequenceNumber(seqNum), timePoint(tPoint) {};
        
        SequenceNumber sequenceNumber;
        p_high_resolution_clock::time_point timePoint;
        bool wasResent { false };
    };
 
    using PacketTimeList = std::vector<SentPacketData>;
    PacketTimeList _sentPacketDatas; // association of sequence numbers to sent time, for RTT calc
 
    p_high_resolution_clock::time_point _lastAdjustmentTime; // Time of last congestion control adjustment
 
    bool _slowStart { true }; // Marker for slow start phase
 
    SequenceNumber _lastACK; // Sequence number of last packet that was ACKed
 
    int _numACKSinceFastRetransmit { 3 }; // Number of ACKs received since fast re-transmit, default avoids immediate re-transmit
 
    int _currentMinRTT; // Current min RTT during last RTT (since last congestion avoidance check), in microseconds
    int _baseRTT; // Lowest RTT during connection, in microseconds
    int _ewmaRTT { -1 }; // Exponential weighted moving average RTT
    int _rttVariance { 0 }; // Variance in collected RTT values
 
    int _numRTTs { 0 }; // Number of RTTs calculated during the last RTT (since last performed congestion avoidance)
 
    int _ackAICount { 0 }; // Counter for number of ACKs received for Reno additive increase
    int _duplicateACKCount { 0 }; // Counter for duplicate ACKs received
 
    int _slowStartOddAdjust { 0 }; // Marker for every window adjustment every other RTT in slow-start
};
 
}
 
 
 
 
 
#endif // hifi_TCPVegasCC_h