inet::tcp::TCPNewReno Class Reference

Implements TCP NewReno. More...

#include <TCPNewReno.h>

Inheritance diagram for inet::tcp::TCPNewReno:

Public Member Functions
	TCPNewReno ()
	Ctor. More...
virtual void	receivedDataAck (uint32 firstSeqAcked) override
	Redefine what should happen when data got acked, to add congestion window management. More...
virtual void	receivedDuplicateAck () override
	Redefine what should happen when dupAck was received, to add congestion window management. More...
Public Member Functions inherited from inet::tcp::TCPTahoeRenoFamily
	TCPTahoeRenoFamily ()
	Ctor. More...
Public Member Functions inherited from inet::tcp::TCPBaseAlg
	TCPBaseAlg ()
	Ctor. More...
virtual	~TCPBaseAlg ()
	Virtual dtor. More...
virtual void	initialize () override
	Create timers, etc. More...
virtual void	established (bool active) override
	Called when the connection is going to ESTABLISHED from SYN_SENT or SYN_RCVD. More...
virtual void	connectionClosed () override
	Called when the connection closes, it should cancel all running timers. More...
virtual void	processTimer (cMessage *timer, TCPEventCode &event) override
	Process REXMIT, PERSIST, DELAYED-ACK and KEEP-ALIVE timers. More...
virtual void	sendCommandInvoked () override
	Called after user sent TCP_C_SEND command to us. More...
virtual void	receivedOutOfOrderSegment () override
	Called after receiving data which are in the window, but not at its left edge (seq != rcv_nxt). More...
virtual void	receiveSeqChanged () override
	Called after rcv_nxt got advanced, either because we received in-sequence data ("text" in RFC 793 lingo) or a FIN. More...
virtual void	receivedAckForDataNotYetSent (uint32 seq) override
	Called after we received an ACK for data not yet sent. More...
virtual void	ackSent () override
	Called after we sent an ACK. More...
virtual void	dataSent (uint32 fromseq) override
	Called after we sent data. More...
virtual void	segmentRetransmitted (uint32 fromseq, uint32 toseq) override
	Called after we retransmitted segment. More...
virtual void	restartRexmitTimer () override
	Restart REXMIT timer. More...
Public Member Functions inherited from inet::tcp::TCPAlgorithm
	TCPAlgorithm ()
	Ctor. More...
virtual	~TCPAlgorithm ()
	Virtual dtor. More...
void	setConnection (TCPConnection *_conn)
	Assign this object to a TCPConnection. More...
TCPStateVariables *	getStateVariables ()
	Creates and returns the TCP state variables. More...

Protected Member Functions
virtual TCPStateVariables *	createStateVariables () override
	Create and return a TCPNewRenoStateVariables object. More...
virtual void	recalculateSlowStartThreshold ()
	Utility function to recalculate ssthresh. More...
virtual void	processRexmitTimer (TCPEventCode &event) override
	Redefine what should happen on retransmission. More...
Protected Member Functions inherited from inet::tcp::TCPBaseAlg
virtual void	startRexmitTimer ()
	Start REXMIT timer and initialize retransmission variables. More...
virtual void	rttMeasurementComplete (simtime_t tSent, simtime_t tAcked)
	Update state vars with new measured RTT value. More...
virtual void	rttMeasurementCompleteUsingTS (uint32 echoedTS) override
	Converting uint32 echoedTS to simtime_t and calling rttMeasurementComplete() to update state vars with new measured RTT value. More...
virtual bool	sendData (bool sendCommandInvoked)
	Send data, observing Nagle's algorithm and congestion window. More...
cMessage *	cancelEvent (cMessage *msg)
	Utility function. More...
virtual void	processPersistTimer (TCPEventCode &event)
virtual void	processDelayedAckTimer (TCPEventCode &event)
virtual void	processKeepAliveTimer (TCPEventCode &event)

Protected Attributes
TCPNewRenoStateVariables *&	state
Protected Attributes inherited from inet::tcp::TCPTahoeRenoFamily
TCPTahoeRenoFamilyStateVariables *&	state
Protected Attributes inherited from inet::tcp::TCPBaseAlg
TCPBaseAlgStateVariables *&	state
cMessage *	rexmitTimer
cMessage *	persistTimer
cMessage *	delayedAckTimer
cMessage *	keepAliveTimer
cOutVector *	cwndVector
cOutVector *	ssthreshVector
cOutVector *	rttVector
cOutVector *	srttVector
cOutVector *	rttvarVector
cOutVector *	rtoVector
cOutVector *	numRtosVector
Protected Attributes inherited from inet::tcp::TCPAlgorithm
TCPConnection *	conn
TCPStateVariables *	state

Detailed Description

Implements TCP NewReno.

Constructor & Destructor Documentation

inet::tcp::TCPNewReno::TCPNewReno

(

)

Ctor.

                       : TCPTahoeRenoFamily(),
    state((TCPNewRenoStateVariables *&)TCPAlgorithm::state)
{
}

Member Function Documentation

virtual TCPStateVariables* inet::tcp::TCPNewReno::createStateVariables ( )

inlineoverrideprotectedvirtual

Create and return a TCPNewRenoStateVariables object.

Implements inet::tcp::TCPAlgorithm.

    {
        return new TCPNewRenoStateVariables();
    }

void inet::tcp::TCPNewReno::processRexmitTimer ( TCPEventCode &  event )

overrideprotectedvirtual

Redefine what should happen on retransmission.

Reimplemented from inet::tcp::TCPBaseAlg.

{
    TCPTahoeRenoFamily::processRexmitTimer(event);

    if (event == TCP_E_ABORT)
        return;

    // RFC 3782, page 6:
    // "6)  Retransmit timeouts:
    // After a retransmit timeout, record the highest sequence number
    // transmitted in the variable "recover" and exit the Fast Recovery
    // procedure if applicable."
    state->recover = (state->snd_max - 1);
    EV_INFO << "recover=" << state->recover << "\n";
    state->lossRecovery = false;
    state->firstPartialACK = false;
    EV_INFO << "Loss Recovery terminated.\n";

    // After REXMIT timeout TCP NewReno should start slow start with snd_cwnd = snd_mss.
    //
    // If calling "retransmitData();" there is no rexmit limitation (bytesToSend > snd_cwnd)
    // therefore "sendData();" has been modified and is called to rexmit outstanding data.
    //
    // RFC 2581, page 5:
    // "Furthermore, upon a timeout cwnd MUST be set to no more than the loss
    // window, LW, which equals 1 full-sized segment (regardless of the
    // value of IW).  Therefore, after retransmitting the dropped segment
    // the TCP sender uses the slow start algorithm to increase the window
    // from 1 full-sized segment to the new value of ssthresh, at which
    // point congestion avoidance again takes over."

    // begin Slow Start (RFC 2581)
    recalculateSlowStartThreshold();
    state->snd_cwnd = state->snd_mss;

    if (cwndVector)
        cwndVector->record(state->snd_cwnd);

    EV_INFO << "Begin Slow Start: resetting cwnd to " << state->snd_cwnd
            << ", ssthresh=" << state->ssthresh << "\n";
    state->afterRto = true;
    conn->retransmitOneSegment(true);
}

void inet::tcp::TCPNewReno::recalculateSlowStartThreshold ( )

protectedvirtual

Utility function to recalculate ssthresh.

Referenced by processRexmitTimer(), and receivedDuplicateAck().

{
    // RFC 2581, page 4:
    // "When a TCP sender detects segment loss using the retransmission
    // timer, the value of ssthresh MUST be set to no more than the value
    // given in equation 3:
    //
    //   ssthresh = max (FlightSize / 2, 2*SMSS)            (3)
    //
    // As discussed above, FlightSize is the amount of outstanding data in
    // the network."

    // set ssthresh to flight size / 2, but at least 2 SMSS
    // (the formula below practically amounts to ssthresh = cwnd / 2 most of the time)
    uint32 flight_size = std::min(state->snd_cwnd, state->snd_wnd);    // FIXME TODO - Does this formula computes the amount of outstanding data?
    // uint32 flight_size = state->snd_max - state->snd_una;
    state->ssthresh = std::max(flight_size / 2, 2 * state->snd_mss);

    if (ssthreshVector)
        ssthreshVector->record(state->ssthresh);
}

void inet::tcp::TCPNewReno::receivedDataAck ( uint32  firstSeqAcked )

overridevirtual

Redefine what should happen when data got acked, to add congestion window management.

Reimplemented from inet::tcp::TCPBaseAlg.

{
    TCPTahoeRenoFamily::receivedDataAck(firstSeqAcked);

    // RFC 3782, page 5:
    // "5) When an ACK arrives that acknowledges new data, this ACK could be
    // the acknowledgment elicited by the retransmission from step 2, or
    // elicited by a later retransmission.
    //
    // Full acknowledgements:
    // If this ACK acknowledges all of the data up to and including
    // "recover", then the ACK acknowledges all the intermediate
    // segments sent between the original transmission of the lost
    // segment and the receipt of the third duplicate ACK.  Set cwnd to
    // either (1) min (ssthresh, FlightSize + SMSS) or (2) ssthresh,
    // where ssthresh is the value set in step 1; this is termed
    // "deflating" the window.  (We note that "FlightSize" in step 1
    // referred to the amount of data outstanding in step 1, when Fast
    // Recovery was entered, while "FlightSize" in step 5 refers to the
    // amount of data outstanding in step 5, when Fast Recovery is
    // exited.)  If the second option is selected, the implementation is
    // encouraged to take measures to avoid a possible burst of data, in
    // case the amount of data outstanding in the network is much less
    // than the new congestion window allows.  A simple mechanism is to
    // limit the number of data packets that can be sent in response to
    // a single acknowledgement; this is known as "maxburst_" in the NS
    // simulator.  Exit the Fast Recovery procedure."
    if (state->lossRecovery) {
        if (seqGE(state->snd_una - 1, state->recover)) {
            // Exit Fast Recovery: deflating cwnd
            //
            // option (1): set cwnd to min (ssthresh, FlightSize + SMSS)
            uint32 flight_size = state->snd_max - state->snd_una;
            state->snd_cwnd = std::min(state->ssthresh, flight_size + state->snd_mss);
            EV_INFO << "Fast Recovery - Full ACK received: Exit Fast Recovery, setting cwnd to " << state->snd_cwnd << "\n";
            // option (2): set cwnd to ssthresh
            // state->snd_cwnd = state->ssthresh;
            // tcpEV << "Fast Recovery - Full ACK received: Exit Fast Recovery, setting cwnd to ssthresh=" << state->ssthresh << "\n";
            // TODO - If the second option (2) is selected, take measures to avoid a possible burst of data (maxburst)!
            if (cwndVector)
                cwndVector->record(state->snd_cwnd);

            state->lossRecovery = false;
            state->firstPartialACK = false;
            EV_INFO << "Loss Recovery terminated.\n";
        }
        else {
            // RFC 3782, page 5:
            // "Partial acknowledgements:
            // If this ACK does *not* acknowledge all of the data up to and
            // including "recover", then this is a partial ACK.  In this case,
            // retransmit the first unacknowledged segment.  Deflate the
            // congestion window by the amount of new data acknowledged by the
            // cumulative acknowledgement field.  If the partial ACK
            // acknowledges at least one SMSS of new data, then add back SMSS
            // bytes to the congestion window.  As in Step 3, this artificially
            // inflates the congestion window in order to reflect the additional
            // segment that has left the network.  Send a new segment if
            // permitted by the new value of cwnd.  This "partial window
            // deflation" attempts to ensure that, when Fast Recovery eventually
            // ends, approximately ssthresh amount of data will be outstanding
            // in the network.  Do not exit the Fast Recovery procedure (i.e.,
            // if any duplicate ACKs subsequently arrive, execute Steps 3 and 4
            // above).
            //
            // For the first partial ACK that arrives during Fast Recovery, also
            // reset the retransmit timer.  Timer management is discussed in
            // more detail in Section 4."

            EV_INFO << "Fast Recovery - Partial ACK received: retransmitting the first unacknowledged segment\n";
            // retransmit first unacknowledged segment
            conn->retransmitOneSegment(false);

            // deflate cwnd by amount of new data acknowledged by cumulative acknowledgement field
            state->snd_cwnd -= state->snd_una - firstSeqAcked;

            if (cwndVector)
                cwndVector->record(state->snd_cwnd);

            EV_INFO << "Fast Recovery: deflating cwnd by amount of new data acknowledged, new cwnd=" << state->snd_cwnd << "\n";

            // if the partial ACK acknowledges at least one SMSS of new data, then add back SMSS bytes to the cwnd
            if (state->snd_una - firstSeqAcked >= state->snd_mss) {
                state->snd_cwnd += state->snd_mss;

                if (cwndVector)
                    cwndVector->record(state->snd_cwnd);

                EV_DETAIL << "Fast Recovery: inflating cwnd by SMSS, new cwnd=" << state->snd_cwnd << "\n";
            }

            // try to send a new segment if permitted by the new value of cwnd
            sendData(false);

            // reset REXMIT timer for the first partial ACK that arrives during Fast Recovery
            if (state->lossRecovery) {
                if (!state->firstPartialACK) {
                    state->firstPartialACK = true;
                    EV_DETAIL << "First partial ACK arrived during recovery, restarting REXMIT timer.\n";
                    restartRexmitTimer();
                }
            }
        }
    }
    else {
        //
        // Perform slow start and congestion avoidance.
        //
        if (state->snd_cwnd < state->ssthresh) {
            EV_DETAIL << "cwnd <= ssthresh: Slow Start: increasing cwnd by SMSS bytes to ";

            // perform Slow Start. RFC 2581: "During slow start, a TCP increments cwnd
            // by at most SMSS bytes for each ACK received that acknowledges new data."
            state->snd_cwnd += state->snd_mss;

            // Note: we could increase cwnd based on the number of bytes being
            // acknowledged by each arriving ACK, rather than by the number of ACKs
            // that arrive. This is called "Appropriate Byte Counting" (ABC) and is
            // described in RFC 3465. This RFC is experimental and probably not
            // implemented in real-life TCPs, hence it's commented out. Also, the ABC
            // RFC would require other modifications as well in addition to the
            // two lines below.
            //
            // int bytesAcked = state->snd_una - firstSeqAcked;
            // state->snd_cwnd += bytesAcked * state->snd_mss;

            if (cwndVector)
                cwndVector->record(state->snd_cwnd);

            EV_DETAIL << "cwnd=" << state->snd_cwnd << "\n";
        }
        else {
            // perform Congestion Avoidance (RFC 2581)
            uint32 incr = state->snd_mss * state->snd_mss / state->snd_cwnd;

            if (incr == 0)
                incr = 1;

            state->snd_cwnd += incr;

            if (cwndVector)
                cwndVector->record(state->snd_cwnd);

            //
            // Note: some implementations use extra additive constant mss / 8 here
            // which is known to be incorrect (RFC 2581 p5)
            //
            // Note 2: RFC 3465 (experimental) "Appropriate Byte Counting" (ABC)
            // would require maintaining a bytes_acked variable here which we don't do
            //

            EV_DETAIL << "cwnd > ssthresh: Congestion Avoidance: increasing cwnd linearly, to " << state->snd_cwnd << "\n";
        }

        // RFC 3782, page 13:
        // "When not in Fast Recovery, the value of the state variable "recover"
        // should be pulled along with the value of the state variable for
        // acknowledgments (typically, "snd_una") so that, when large amounts of
        // data have been sent and acked, the sequence space does not wrap and
        // falsely indicate that Fast Recovery should not be entered (Section 3,
        // step 1, last paragraph)."
        state->recover = (state->snd_una - 2);
    }

    sendData(false);
}

void inet::tcp::TCPNewReno::receivedDuplicateAck ( )

overridevirtual

Redefine what should happen when dupAck was received, to add congestion window management.

Reimplemented from inet::tcp::TCPBaseAlg.

{
    TCPTahoeRenoFamily::receivedDuplicateAck();

    if (state->dupacks == DUPTHRESH) {    // DUPTHRESH = 3
        if (!state->lossRecovery) {
            // RFC 3782, page 4:
            // "1) Three duplicate ACKs:
            // When the third duplicate ACK is received and the sender is not
            // already in the Fast Recovery procedure, check to see if the
            // Cumulative Acknowledgement field covers more than "recover".  If
            // so, go to Step 1A.  Otherwise, go to Step 1B."
            //
            // RFC 3782, page 6:
            // "Step 1 specifies a check that the Cumulative Acknowledgement field
            // covers more than "recover".  Because the acknowledgement field
            // contains the sequence number that the sender next expects to receive,
            // the acknowledgement "ack_number" covers more than "recover" when:
            //      ack_number - 1 > recover;"
            if (state->snd_una - 1 > state->recover) {
                EV_INFO << "NewReno on dupAcks == DUPTHRESH(=3): perform Fast Retransmit, and enter Fast Recovery:";

                // RFC 3782, page 4:
                // "1A) Invoking Fast Retransmit:
                // If so, then set ssthresh to no more than the value given in
                // equation 1 below.  (This is equation 3 from [RFC2581]).
                //      ssthresh = max (FlightSize / 2, 2*SMSS)           (1)
                // In addition, record the highest sequence number transmitted in
                // the variable "recover", and go to Step 2."
                recalculateSlowStartThreshold();
                state->recover = (state->snd_max - 1);
                state->firstPartialACK = false;
                state->lossRecovery = true;
                EV_INFO << " set recover=" << state->recover;

                // RFC 3782, page 4:
                // "2) Entering Fast Retransmit:
                // Retransmit the lost segment and set cwnd to ssthresh plus 3 * SMSS.
                // This artificially "inflates" the congestion window by the number
                // of segments (three) that have left the network and the receiver
                // has buffered."
                state->snd_cwnd = state->ssthresh + 3 * state->snd_mss;

                if (cwndVector)
                    cwndVector->record(state->snd_cwnd);

                EV_DETAIL << " , cwnd=" << state->snd_cwnd << ", ssthresh=" << state->ssthresh << "\n";
                conn->retransmitOneSegment(false);

                // RFC 3782, page 5:
                // "4) Fast Recovery, continued:
                // Transmit a segment, if allowed by the new value of cwnd and the
                // receiver's advertised window."
                sendData(false);
            }
            else {
                EV_INFO << "NewReno on dupAcks == DUPTHRESH(=3): not invoking Fast Retransmit and Fast Recovery\n";

                // RFC 3782, page 4:
                // "1B) Not invoking Fast Retransmit:
                // Do not enter the Fast Retransmit and Fast Recovery procedure.  In
                // particular, do not change ssthresh, do not go to Step 2 to
                // retransmit the "lost" segment, and do not execute Step 3 upon
                // subsequent duplicate ACKs."
            }
        }
        EV_INFO << "NewReno on dupAcks == DUPTHRESH(=3): TCP is already in Fast Recovery procedure\n";
    }
    else if (state->dupacks > DUPTHRESH) {    // DUPTHRESH = 3
        if (state->lossRecovery) {
            // RFC 3782, page 4:
            // "3) Fast Recovery:
            // For each additional duplicate ACK received while in Fast
            // Recovery, increment cwnd by SMSS.  This artificially inflates the
            // congestion window in order to reflect the additional segment that
            // has left the network."
            state->snd_cwnd += state->snd_mss;

            if (cwndVector)
                cwndVector->record(state->snd_cwnd);

            EV_DETAIL << "NewReno on dupAcks > DUPTHRESH(=3): Fast Recovery: inflating cwnd by SMSS, new cwnd=" << state->snd_cwnd << "\n";

            // RFC 3782, page 5:
            // "4) Fast Recovery, continued:
            // Transmit a segment, if allowed by the new value of cwnd and the
            // receiver's advertised window."
            sendData(false);
        }
    }
}

Member Data Documentation

TCPNewRenoStateVariables*& inet::tcp::TCPNewReno::state

protected

Referenced by processRexmitTimer(), recalculateSlowStartThreshold(), receivedDataAck(), and receivedDuplicateAck().

---

The documentation for this class was generated from the following files:

• TCPNewReno.h
• TCPNewReno.cc