tcp-socket-state.h

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/*
 * Copyright (c) 2018 Natale Patriciello <natale.patriciello@gmail.com>
 *
 * SPDX-License-Identifier: GPL-2.0-only
 */
#ifndef TCP_SOCKET_STATE_H
#define TCP_SOCKET_STATE_H
 
#include "tcp-rx-buffer.h"
 
#include "ns3/data-rate.h"
#include "ns3/object.h"
#include "ns3/sequence-number.h"
#include "ns3/traced-value.h"
 
namespace ns3
{
 
/**
 * \brief Data structure that records the congestion state of a connection
 *
 * In this data structure, basic information that should be passed between
 * socket and the congestion control algorithm are saved. Through the code,
 * it will be referred as Transmission Control Block (TCB), but there are some
 * differences. In the RFCs, the TCB contains all the variables that defines
 * a connection, while we preferred to maintain in this class only the values
 * that should be exchanged between socket and other parts, like congestion
 * control algorithms.
 *
 */
class TcpSocketState : public Object
{
  public:
    /**
     * Get the type ID.
     * \brief Get the type ID.
     * \return the object TypeId
     */
    static TypeId GetTypeId();
 
    /**
     * \brief TcpSocketState Constructor
     */
    TcpSocketState()
        : Object()
    {
    }
 
    /**
     * \brief Copy constructor.
     * \param other object to copy.
     */
    TcpSocketState(const TcpSocketState& other);
 
    /**
     * \brief Definition of the Congestion state machine
     *
     * The design of this state machine is taken from Linux v4.0, but it has been
     * maintained in the Linux mainline from ages. It basically avoids to maintain
     * a lot of boolean variables, and it allows to check the transitions from
     * different algorithm in a cleaner way.
     *
     * These states represent the situation from a congestion control point of view:
     * in fact, apart the CA_OPEN state, the other states represent a situation in
     * which there is a congestion, and different actions should be taken,
     * depending on the case.
     *
     */
    enum TcpCongState_t
    {
        CA_OPEN,     //!< Normal state, no dubious events
        CA_DISORDER, //!< In all the respects it is "Open",
                     //!< but requires a bit more attention. It is entered when we see some SACKs or
                     //!< dupacks. It is split of "Open".
        CA_CWR,      //!< cWnd was reduced due to some congestion notification event, such as ECN,
                     //!< ICMP source quench, local device congestion.
        CA_RECOVERY, //!< CWND was reduced, we are fast-retransmitting.
        CA_LOSS,     //!< CWND was reduced due to RTO timeout or SACK reneging.
        CA_LAST_STATE //!< Used only in debug messages
    };
 
    // Note: "not triggered" events are currently not triggered by the code.
    /**
     * \brief Congestion avoidance events
     */
    enum TcpCAEvent_t
    {
        CA_EVENT_TX_START,        //!< first transmit when no packets in flight
        CA_EVENT_CWND_RESTART,    //!< congestion window restart. Not triggered
        CA_EVENT_COMPLETE_CWR,    //!< end of congestion recovery
        CA_EVENT_LOSS,            //!< loss timeout
        CA_EVENT_ECN_NO_CE,       //!< ECT set, but not CE marked. Not triggered
        CA_EVENT_ECN_IS_CE,       //!< received CE marked IP packet. Not triggered
        CA_EVENT_DELAYED_ACK,     //!< Delayed ack is sent
        CA_EVENT_NON_DELAYED_ACK, //!< Non-delayed ack is sent
    };
 
    /**
     * \brief Parameter value related to ECN enable/disable functionality
     *        similar to sysctl for tcp_ecn. Currently value 2 from
     *        https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt
     *        is not implemented.
     */
    enum UseEcn_t
    {
        Off = 0,        //!< Disable
        On = 1,         //!< Enable
        AcceptOnly = 2, //!< Enable only when the peer endpoint is ECN capable
    };
 
    /**
     * \brief ECN code points
     */
    enum EcnCodePoint_t
    {
        NotECT = 0,  //!< Unmarkable
        Ect1 = 1,    //!< Markable
        Ect0 = 2,    //!< Markable
        CongExp = 3, //!< Marked
    };
 
    /**
     * \brief ECN Modes
     */
    enum EcnMode_t
    {
        ClassicEcn, //!< ECN functionality as described in RFC 3168.
        DctcpEcn,   //!< ECN functionality as described in RFC 8257. Note: this mode is specific to
                    //!< DCTCP.
    };
 
    /**
     * \brief Definition of the Ecn state machine
     *
     */
    enum EcnState_t
    {
        ECN_DISABLED = 0, //!< ECN disabled traffic
        ECN_IDLE, //!< ECN is enabled  but currently there is no action pertaining to ECE or CWR to
                  //!< be taken
        ECN_CE_RCVD,     //!< Last packet received had CE bit set in IP header
        ECN_SENDING_ECE, //!< Receiver sends an ACK with ECE bit set in TCP header
        ECN_ECE_RCVD,    //!< Last ACK received had ECE bit set in TCP header
        ECN_CWR_SENT //!< Sender has reduced the congestion window, and sent a packet with CWR bit
                     //!< set in TCP header. This state is used for tracing.
    };
 
    /**
     * \brief Literal names of TCP states for use in log messages
     */
    static const char* const TcpCongStateName[TcpSocketState::CA_LAST_STATE];
 
    /**
     * \brief Literal names of ECN states for use in log messages
     */
    static const char* const EcnStateName[TcpSocketState::ECN_CWR_SENT + 1];
 
    // Congestion control
    TracedValue<uint32_t> m_cWnd{0}; //!< Congestion window
    TracedValue<uint32_t> m_cWndInfl{
        0}; //!< Inflated congestion window trace (used only for backward compatibility purpose)
    TracedValue<uint32_t> m_ssThresh{0}; //!< Slow start threshold
    uint32_t m_initialCWnd{0};           //!< Initial cWnd value
    uint32_t m_initialSsThresh{0};       //!< Initial Slow Start Threshold value
 
    // Recovery
    // This variable is used for implementing following flag of Linux: FLAG_RETRANS_DATA_ACKED
    // and is used only during a recovery phase to keep track of acknowledgement of retransmitted
    // packet.
    bool m_isRetransDataAcked{false}; //!< Retransmitted data is ACKed if true
 
    // Segment
    uint32_t m_segmentSize{0};          //!< Segment size
    SequenceNumber32 m_lastAckedSeq{0}; //!< Last sequence ACKed
 
    TracedValue<TcpCongState_t> m_congState{CA_OPEN}; //!< State in the Congestion state machine
 
    TracedValue<EcnState_t> m_ecnState{
        ECN_DISABLED}; //!< Current ECN State, represented as combination of EcnState values
 
    TracedValue<SequenceNumber32> m_highTxMark{0}; //!< Highest seqno ever sent, regardless of ReTx
    TracedValue<SequenceNumber32> m_nextTxSequence{
        0}; //!< Next seqnum to be sent (SND.NXT), ReTx pushes it back
 
    uint32_t m_rcvTimestampValue{0};     //!< Receiver Timestamp value
    uint32_t m_rcvTimestampEchoReply{0}; //!< Sender Timestamp echoed by the receiver
 
    // Pacing related variables
    bool m_pacing{false};                  //!< Pacing status
    DataRate m_maxPacingRate{0};           //!< Max Pacing rate
    TracedValue<DataRate> m_pacingRate{0}; //!< Current Pacing rate
    uint16_t m_pacingSsRatio{0};           //!< SS pacing ratio
    uint16_t m_pacingCaRatio{0};           //!< CA pacing ratio
    bool m_paceInitialWindow{false};       //!< Enable/Disable pacing for the initial window
 
    Time m_minRtt{Time::Max()}; //!< Minimum RTT observed throughout the connection
 
    TracedValue<uint32_t> m_bytesInFlight{0}; //!< Bytes in flight
    bool m_isCwndLimited{false};              //!< Whether throughput is limited by cwnd
    TracedValue<Time> m_srtt;                 //!< Smoothed RTT
    TracedValue<Time> m_lastRtt;              //!< RTT of the last (S)ACKed packet
 
    Ptr<TcpRxBuffer> m_rxBuffer; //!< Rx buffer (reordering buffer)
 
    EcnMode_t m_ecnMode{ClassicEcn}; //!< ECN mode
    UseEcn_t m_useEcn{Off};          //!< Socket ECN capability
 
    EcnCodePoint_t m_ectCodePoint{Ect0}; //!< ECT code point to use
 
    uint32_t m_lastAckedSackedBytes{
        0}; //!< The number of bytes acked and sacked as indicated by the current ACK received. This
            //!< is similar to acked_sacked variable in Linux
 
    /**
     * \brief Get cwnd in segments rather than bytes
     *
     * \return Congestion window in segments
     */
    uint32_t GetCwndInSegments() const
    {
        return m_cWnd / m_segmentSize;
    }
 
    /**
     * \brief Get slow start thresh in segments rather than bytes
     *
     * \return Slow start threshold in segments
     */
    uint32_t GetSsThreshInSegments() const
    {
        return m_ssThresh / m_segmentSize;
    }
 
    /**
     * Callback to send an empty packet
     */
    Callback<void, uint8_t> m_sendEmptyPacketCallback;
};
 
namespace TracedValueCallback
{
 
/**
 * \ingroup tcp
 * TracedValue Callback signature for TcpCongState_t
 *
 * \param [in] oldValue original value of the traced variable
 * \param [in] newValue new value of the traced variable
 */
typedef void (*TcpCongState)(const TcpSocketState::TcpCongState_t oldValue,
                             const TcpSocketState::TcpCongState_t newValue);
 
/**
 * \ingroup tcp
 * TracedValue Callback signature for EcnState_t
 *
 * \param [in] oldValue original value of the traced variable
 * \param [in] newValue new value of the traced variable
 */
typedef void (*EcnState)(const TcpSocketState::EcnState_t oldValue,
                         const TcpSocketState::EcnState_t newValue);
 
} // namespace TracedValueCallback
 
} // namespace ns3
 
#endif /* TCP_SOCKET_STATE_H */