TCPTahoe Class Reference

#include <TCPTahoe.h>

Inheritance diagram for TCPTahoe:

List of all members.

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Detailed Description

Implements Tahoe.

Public Member Functions
	TCPTahoe ()
virtual void	receivedDataAck (uint32 firstSeqAcked)
virtual void	receivedDuplicateAck ()
Protected Member Functions
virtual TCPStateVariables *	createStateVariables ()
void	recalculateSlowStartThreshold ()
virtual void	processRexmitTimer (TCPEventCode &event)
Protected Attributes
TCPTahoeStateVariables *&	state

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Constructor & Destructor Documentation

TCPTahoe::TCPTahoe (   )

Ctor : TCPTahoeRenoFamily(), state((TCPTahoeStateVariables *&)TCPAlgorithm::state) { }

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Member Function Documentation

virtual TCPStateVariables* TCPTahoe::createStateVariables (   )  [inline, protected, virtual]

Create and return a TCPTahoeStateVariables object. Implements TCPAlgorithm. { return new TCPTahoeStateVariables(); }

void TCPTahoe::processRexmitTimer (  TCPEventCode &  event  )  [protected, virtual]

Redefine what should happen on retransmission Reimplemented from TCPBaseAlg. { TCPTahoeRenoFamily::processRexmitTimer(event); if (event==TCP_E_ABORT) return; // begin Slow Start (RFC2001) recalculateSlowStartThreshold(); state->snd_cwnd = state->snd_mss; if (cwndVector) cwndVector->record(state->snd_cwnd); tcpEV << "Begin Slow Start: resetting cwnd to " << state->snd_cwnd << ", ssthresh=" << state->ssthresh << "\n"; // Tahoe retransmits only one segment at the front of the queue conn->retransmitOneSegment(); }

void TCPTahoe::recalculateSlowStartThreshold (   )  [protected]

Utility function to recalculate ssthresh { // set ssthresh to flight size/2, but at least 2 MSS // (the formula below practically amounts to ssthresh=cwnd/2 most of the time) uint flight_size = Min(state->snd_cwnd, state->snd_wnd); state->ssthresh = Max(flight_size/2, 2*state->snd_mss); if (ssthreshVector) ssthreshVector->record(state->ssthresh); }

void TCPTahoe::receivedDataAck (  uint32  firstSeqAcked  )  [virtual]

Redefine what should happen when data got acked, to add congestion window management Reimplemented from TCPBaseAlg. { TCPTahoeRenoFamily::receivedDataAck(firstSeqAcked); // // Perform slow start and congestion avoidance. // if (state->snd_cwnd < state->ssthresh) { tcpEV << "cwnd<=ssthresh: Slow Start: increasing cwnd by one segment, 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 (experimental). // // int bytesAcked = state->snd_una - firstSeqAcked; // state->snd_cwnd += bytesAcked; if (cwndVector) cwndVector->record(state->snd_cwnd); tcpEV << "cwnd=" << state->snd_cwnd << "\n"; } else { // perform Congestion Avoidance (rfc 2581) int 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 // tcpEV << "cwnd>ssthresh: Congestion Avoidance: increasing cwnd linearly, to " << state->snd_cwnd << "\n"; } // ack and/or cwnd increase may have freed up some room in the window, try sending sendData(); }

void TCPTahoe::receivedDuplicateAck (   )  [virtual]

Redefine what should happen when dupAck was received, to add congestion window management Reimplemented from TCPBaseAlg. { TCPTahoeRenoFamily::receivedDuplicateAck(); if (state->dupacks==3) { tcpEV << "Tahoe on dupAck=3: perform Fast Retransmit, and enter Slow Start:\n"; // Fast Retransmission: retransmit missing segment without waiting // for the REXMIT timer to expire conn->retransmitOneSegment(); // enter Slow Start recalculateSlowStartThreshold(); state->snd_cwnd = state->snd_mss; if (cwndVector) cwndVector->record(state->snd_cwnd); tcpEV << "Set cwnd=" << state->snd_cwnd << ", ssthresh=" << state->ssthresh << "\n"; // FIXME FIXME FIXME FIXME FIXME FIXME FIXME FIXME FIXME FIXME FIXME FIXME // double-check if Tahoe really restarts REXMIT timer here // // restart retransmission timer (with rexmit_count=0), and cancel round-trip time measurement // (see p972 "29.4 Fast Retransmit and Fast Recovery Algorithms" of // TCP/IP Illustrated, Vol2) -- but that's probably New Reno cancelEvent(rexmitTimer); startRexmitTimer(); state->rtseq_sendtime = 0; } }

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Member Data Documentation

TCPTahoeStateVariables*& TCPTahoe::state [protected]

Reimplemented from TCPTahoeRenoFamily.

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

• TCPTahoe.h
• TCPTahoe.cc

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