TrafficControl.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
// Includes
#include "CoreMinimal.h"
#include "Net/Util/SequenceNumber.h"
#include "Net/Core/Misc/ResizableCircularQueue.h"
#include "EngineLogs.h"
 
 
struct FAckSample;
struct FSeqSample;
class FNetworkTrafficAnalyzer;
class FNetworkCongestionControl;
 
struct FSeqSample
{
    double Timestamp;
    int32 Seq;
    int32 PacketSize;
};
 
struct FAckSample
{
    double Timestamp;
    int32 Ack;
};
 
class FNetworkTrafficAnalyzer
{
public:
    ENGINE_API FNetworkTrafficAnalyzer(FNetworkCongestionControl* InTrafficControlModule);
 
    ENGINE_API void OnAck(const FAckSample& AckSample);
    ENGINE_API void OnSend(const FSeqSample& SeqSample);
 
    double GetLatestRTT() const { return LatestRTT; }
    uint32 GetBytesInFlight() const { return BytesInFlight; }
    uint32 GetPacketsInFlight() const { return (uint32)OutPacketRecords.Count(); }
 
private:
    FNetworkCongestionControl* TrafficControlModule;
 
    TResizableCircularQueue<FSeqSample> OutPacketRecords;
 
    using SeqT = TSequenceNumber<8, uint8>;
 
    double LatestUplinkBandwidth;
    double LatestRTT;
    SeqT OutSeq;                    // The seq number of last sent packet.
    SeqT OutAckedSeq;               // The seq number of last acked packet.
    // Number of unacked bytes which is the sum of all packet size
    // in the OutPacketRecords.
    uint32 BytesInFlight;
    bool bInitialized;              // Whether the first packet has been sent.
};
 
class FNetworkCongestionControl
{
public:
    ENGINE_API FNetworkCongestionControl(double ConfiguredNetSpeed, uint32 MaxPackets);
 
    ENGINE_API void OnAck(const FAckSample& AckSample);
    ENGINE_API bool IsReadyToSend(double Timestamp) const;
    ENGINE_API void OnSend(const FSeqSample& SeqSample);
 
private:
    FNetworkTrafficAnalyzer Analyzer;
 
    double MinRTT;                                  // Estimated propagation round-trip time in s.
    double NetSpeed;                                // Configured uplink bandwidth in bytes/sec.
    uint32 MaxPacketsAllowedInFlight;               // Max allowed packets in flight, typically the HistorySize of TSequenceHistory.
 
private:
    void UpdateMinRTT(double Timestamp);
    double GetMinRTT() const;
    double GetCongestionWindow() const;
};