tcp-sack1.cc

Ns2 TCP 协议改进 版本 提高goodput

/* -*-	Mode:C++; c-basic-offset:8; tab-width:8; indent-tabs-mode:t -*- */
/*
 * Copyright (c) 1990, 1997 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Lawrence Berkeley Laboratory,
 * Berkeley, CA.  The name of the University may not be used to
 * endorse or promote products derived from this software without
 * specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */

/* 8/02 Tom Kelly - Made scoreboard a general interface to allow
 *                  easy swapping of scoreboard algorithms.  
 */

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>

#include "ip.h"
#include "tcp.h"
#include "flags.h"
#include "scoreboard.h"
#include "scoreboard-rq.h"
#include "random.h"

#define TRUE    1
#define FALSE   0
#define RECOVER_DUPACK  1
#define RECOVER_TIMEOUT 2
#define RECOVER_QUENCH  3

class Sack1TcpAgent : public TcpAgent {
 public:
	Sack1TcpAgent();
	virtual ~Sack1TcpAgent();
	virtual void recv(Packet *pkt, Handler*);
	int is_sacked(hdr_tcp *tcph, int seqlo, int seqhi);
	void reset();
	virtual void timeout(int tno);
	virtual void dupack_action();
	virtual void partial_ack_action();
	void plot();
	virtual void send_much(int force, int reason, int maxburst);
 protected:
	u_char timeout_;	/* boolean: sent pkt from timeout? */
	u_char fastrecov_;	/* boolean: doing fast recovery? */
	int pipe_;		/* estimate of pipe size (fast recovery) */ 
	int partial_ack_;	/* Set to "true" to ensure sending */
				/*  a packet on a partial ACK.     */
	int next_pkt_;		/* Next packet to transmit during Fast */
				/*  Retransmit as a result of a partial ack. */
	int firstpartial_;	/* First of a series of partial acks. */
	ScoreBoard* scb_;
	static const int SBSIZE=64; /* Initial scoreboard size */
};

static class Sack1TcpClass : public TclClass {
public:
	Sack1TcpClass() : TclClass("Agent/TCP/Sack1") {}
	TclObject* create(int, const char*const*) {		
		return (new Sack1TcpAgent());
	}
} class_sack;

Sack1TcpAgent::Sack1TcpAgent() : fastrecov_(FALSE), pipe_(-1), next_pkt_(0), firstpartial_(0)
{
	bind_bool("partial_ack_", &partial_ack_);
	/* Use the Reassembly Queue based scoreboard as
	 * ScoreBoard is O(cwnd) which is bad for HSTCP
	 * scb_ = new ScoreBoard(new ScoreBoardNode[SBSIZE],SBSIZE);
	 */
	scb_ = new ScoreBoardRQ();
}

Sack1TcpAgent::~Sack1TcpAgent(){
	delete scb_;
}

void Sack1TcpAgent::reset ()
{
	scb_->ClearScoreBoard();
	TcpAgent::reset ();
}


void Sack1TcpAgent::recv(Packet *pkt, Handler*)
{
	hdr_tcp *tcph = hdr_tcp::access(pkt);
	int valid_ack = 0;

        if (qs_approved_ == 1 && tcph->seqno() > last_ack_)
		endQuickStart();
        if (qs_requested_ == 1)
                processQuickStart(pkt);
#ifdef notdef
	if (pkt->type_ != PT_ACK) {
		Tcl::instance().evalf("%s error \"received non-ack\"",
				      name());
		Packet::free(pkt);
		return;
	}
#endif
        /* W.N.: check if this is from a previous incarnation */
        if (tcph->ts() < lastreset_) {
                // Remove packet and do nothing
                Packet::free(pkt);
                return;
        }
	++nackpack_;
	int ecnecho = hdr_flags::access(pkt)->ecnecho();
	if (ecnecho && ecn_)
		ecn(tcph->seqno());
        if (tcph->seqno() >= last_ack_)
		// Check if ACK is valid.  Suggestion by Mark Allman.
		valid_ack = 1;
	/*
	 * If DSACK is being used, check for DSACK blocks here.
	 * Possibilities:  Check for unnecessary Fast Retransmits.
	 */
	if (!fastrecov_) {
		/* normal... not fast recovery */
		if ((int)tcph->seqno() > last_ack_) {
			/*
			 * regular ACK not in fast recovery... normal
			 */
			firstpartial_ = 0;
			recv_newack_helper(pkt);
			timeout_ = FALSE;
			scb_->ClearScoreBoard();
			if (last_ack_ == 0 && delay_growth_) {
				cwnd_ = initial_window();
			}
		} else if ((int)tcph->seqno() < last_ack_) {
			/*NOTHING*/
		} else if (timeout_ == FALSE) {
			if (tcph->seqno() != last_ack_) {
				fprintf(stderr, "pkt seq %d should be %d\n" ,
					tcph->seqno(), last_ack_);
				abort();
			}
			scb_->UpdateScoreBoard (highest_ack_, tcph);
			/*
		 	 * Check for a duplicate ACK.
			 * Check that the SACK block actually
			 *  acknowledges new data.
 			 */
 		        if(scb_->CheckUpdate()) {
 			 	if (++dupacks_ == numdupacks(cwnd_)) {
 					/*
 					 * Assume we dropped just one packet.
 					 * Retransmit last ack + 1
 					 * and try to resume the sequence.
 					 */
 				   	dupack_action();
 				} else if (dupacks_ < numdupacks(cwnd_) && singledup_ ) {
					send_one();
 				}
			}
			if (sfrto_enabled_ && frto_ == 2) {
				/*
				 * SACK-based F-RTO: If SACK only acknowledges
				 * data that was transmitted before RTO and
				 * not acknowledged earlier,
				 * the timeout was spurious.
				 */
				if (scb_->IsChanged() &&
				    !is_sacked(tcph, recover_, maxseq_)) {
					spurious_timeout();
				} else {
					t_seqno_ = highest_ack_ + 1;
					cwnd_ = frto_;
					frto_ = 0;
					dupacks_ = 0;
				}
			}
		}
        	if (valid_ack || aggressive_maxburst_)
			if (dupacks_ == 0)
				send_much(FALSE, 0, maxburst_);
	} else {
		/* we are in fast recovery */
		--pipe_;
		if ((int)tcph->seqno() >= recover_) {
			/* ACK indicates fast recovery is over */
			recover_ = 0;
			fastrecov_ = FALSE;
			newack(pkt);
			/* if the connection is done, call finish() */
			if ((highest_ack_ >= curseq_-1) && !closed_) {
				closed_ = 1;
				finish();
			}
			timeout_ = FALSE;
			scb_->ClearScoreBoard();

			/* New window: W/2 - K or W/2? */
		} else if ((int)tcph->seqno() > highest_ack_) {
			/* Not out of fast recovery yet.
			 * Update highest_ack_, but not last_ack_. */
			highest_ack_ = (int)tcph->seqno();
			scb_->UpdateScoreBoard (highest_ack_, tcph);
			if (partial_ack_) {
			  /* partial_ack_ is needed to guarantee that */
			  /*  a new packet is sent in response to a   */
			  /*  partial ack.                            */
				partial_ack_action();
				++pipe_;
				if (firstpartial_ == 0) {
					newtimer(pkt);
					t_backoff_ = 1;
					firstpartial_ = 1;
				}
			} else {
				--pipe_;
				newtimer(pkt);
				t_backoff_ = 1;
 			 /* If this partial ACK is from a retransmitted pkt,*/
 			 /* then we decrement pipe_ again, so that we never */
 			 /* do worse than slow-start.  If this partial ACK  */
 			 /* was instead from the original packet, reordered,*/
 			 /* then this might be too aggressive. */
			}
		} else if (timeout_ == FALSE) {
			/* got another dup ack */
			scb_->UpdateScoreBoard (highest_ack_, tcph);
 		        if(scb_->CheckUpdate()) {
 				if (dupacks_ > 0)
 			        	dupacks_++;
 			}
		}
        	if (valid_ack || aggressive_maxburst_)
			send_much(FALSE, 0, maxburst_);
	}

	Packet::free(pkt);
#ifdef notyet
	if (trace_)
		plot();
#endif
}


/*
 * Returns TRUE if any of the SACK blocks in the current packet (tcph)
 * cover sequence numbers between seqlo and seqhi
 */
int Sack1TcpAgent::is_sacked(hdr_tcp *tcph, int seqlo, int seqhi)
{
	int i, sleft, sright;
	for (i=0; i < tcph->sa_length(); i++) {
		sleft = tcph->sa_left(i);
		sright = tcph->sa_right(i);

		if ((sright > seqlo && sright <= seqhi) ||
		    (sleft >= seqlo && sleft < seqhi) ||
		    (sleft < seqlo && sright > seqhi)) {
			return TRUE;
		}
	}
	return FALSE;
}


void
Sack1TcpAgent::dupack_action()
{
	int recovered = (highest_ack_ > recover_);
	if (recovered || (!bug_fix_ && !ecn_)) {
		goto sack_action;
	}
 
	if (ecn_ && last_cwnd_action_ == CWND_ACTION_ECN) {
		last_cwnd_action_ = CWND_ACTION_DUPACK;
		/*
		 * What if there is a DUPACK action followed closely by ECN
		 * followed closely by a DUPACK action?
		 * The optimal thing to do would be to remember all
		 * congestion actions from the most recent window
		 * of data.  Otherwise "bugfix" might not prevent
		 * all unnecessary Fast Retransmits.
		 */
		reset_rtx_timer(1,0);
		/*
		 * There are three possibilities: 
		 * (1) pipe_ = int(cwnd_) - numdupacks_;
		 * (2) pipe_ = window() - numdupacks_;
		 * (3) pipe_ = maxseq_ - highest_ack_ - numdupacks_;
		 * equation (2) takes into account the receiver's
		 * advertised window, and equation (3) takes into
		 * account a data-limited sender.
		 */
		if (singledup_ && LimTransmitFix_) {
		  pipe_ = maxseq_ - highest_ack_ - 1;
		}
		else {
		  // numdupacks(cwnd_) packets have left the pipe
		  pipe_ = maxseq_ - highest_ack_ - numdupacks(cwnd_);
		}
		fastrecov_ = TRUE;
		scb_->MarkRetran(highest_ack_+1);
		output(last_ack_ + 1, TCP_REASON_DUPACK);
		return;
	}

	if (bug_fix_) {
		/*
		 * The line below, for "bug_fix_" true, avoids
		 * problems with multiple fast retransmits in one
		 * window of data.
		 */
		return;
	}

sack_action:
	recover_ = maxseq_;
	if (oldCode_) {
	 	pipe_ = int(cwnd_) - numdupacks(cwnd_);
	} else if (singledup_ && LimTransmitFix_) {
		  pipe_ = maxseq_ - highest_ack_ - 1;
	}
	else {
		  // numdupacks(cwnd_) packets have left the pipe
		  pipe_ = maxseq_ - highest_ack_ - numdupacks(cwnd_);
	}
	reset_rtx_timer(1,0);
	fastrecov_ = TRUE;
	scb_->MarkRetran(highest_ack_+1);
        if (!lossQuickStart()) {
                // we are now going into fast_recovery and will trace that event
                trace_event("FAST_RECOVERY");
                last_cwnd_action_ = CWND_ACTION_DUPACK;
                slowdown(CLOSE_SSTHRESH_HALF|CLOSE_CWND_HALF);
		output(last_ack_ + 1, TCP_REASON_DUPACK);	// from top
		/*
		 * If dynamically adjusting numdupacks_, record information
		 *  at this point.
		 */
	}
	return;
}

/*
 * Process a packet that acks previously unacknowleges data, but
 * does not take us out of Fast Retransmit.
 *
 * The need for a mechanism to ensure that Sack TCP sends a packet in
 * response to a partial ACK has been discussed in
 * "Challenges to Reliable Data Transport over Heterogeneous
 * Wireless Networks", Hari Balakrishnan, 1998, and in
 * "Responding to Spurious Timeouts in TCP", Andrei Gurtov and 
 * Reiner Ludwig, 2003. 
 */
void
Sack1TcpAgent::partial_ack_action()
{
	if (next_pkt_ < highest_ack_ + 1) {
		next_pkt_ = highest_ack_ + 1;
	}
	// Output two packets in response to a partial ack,
	//   so as not to do worse than slow-start.
	int i;
	for (i = 1; i<=2; i++) {
		int getNext = scb_->GetNextUnacked(next_pkt_);
		if (getNext > next_pkt_) {
			next_pkt_ = getNext;
		}
		if (t_seqno_ < next_pkt_) {
			t_seqno_ = next_pkt_;
		}
		output(next_pkt_, TCP_REASON_PARTIALACK);	
		scb_->MarkRetran(next_pkt_);
		++next_pkt_; 
	}
	return;
}

void Sack1TcpAgent::timeout(int tno)
{
	// F-RTO is not allowed if earlier SACK fast recovery is underway.
	int no_frto = fastrecov_;

	if (tno == TCP_TIMER_RTX) {
		/*
		 * IF DSACK and dynamic adjustment of numdupacks_,
		 *  check whether a smaller value of numdupacks_
		 *  would have prevented this retransmit timeout.
		 * If DSACK and detection of premature retransmit
		 *  timeouts, then save some info here.
		 */ 
		dupacks_ = 0;
		fastrecov_ = FALSE;
		timeout_ = TRUE;
		if (highest_ack_ > last_ack_)
			last_ack_ = highest_ack_;
#ifdef DEBUGSACK1A
		printf ("timeout. highest_ack: %i seqno: %i fid: %i\n", 
			(int)highest_ack_, (int)t_seqno_, fid_);
#endif
		recover_ = maxseq_;
		scb_->ClearScoreBoard();
	}
	TcpAgent::timeout(tno);

	// Overrule frto_ setting that may have been done in TcpAgent
	if (no_frto)
		frto_ = 0;
}

void Sack1TcpAgent::send_much(int force, int reason, int maxburst)
{
	register int found, npacket = 0;
	int win = window();
	int xmit_seqno;

	found = 1;
	if (!force && delsnd_timer_.status() == TIMER_PENDING)
		return;
	/*
	 * as long as the pipe is open and there is app data to send...
	 */
	while (((!fastrecov_ && (t_seqno_ <= last_ack_ + win)) ||
			(fastrecov_ && (pipe_ < int(cwnd_)))) 
			&& t_seqno_ < curseq_ && found) {

		if (overhead_ == 0 || force) {
			found = 0;
			xmit_seqno = scb_->GetNextRetran ();

#ifdef DEBUGSACK1A
			printf("highest_ack: %d xmit_seqno: %d\n", 
			(int)highest_ack_, xmit_seqno);
#endif
			if (xmit_seqno == -1) { 
				if ((!fastrecov_ && t_seqno_<=highest_ack_+win)||
					(fastrecov_ && t_seqno_<=highest_ack_+int(wnd_))) {
					found = 1;
					xmit_seqno = t_seqno_++;
#ifdef DEBUGSACK1A
					printf("sending %d fastrecovery: %d win %d\n",
						xmit_seqno, fastrecov_, win);
#endif
				}
			} else if (recover_>0 && xmit_seqno<=highest_ack_+int(wnd_)) {
				found = 1;
				scb_->MarkRetran (xmit_seqno);
				win = window();
			}
			if (found) {
				output(xmit_seqno, reason);
				if (t_seqno_ <= xmit_seqno)
					t_seqno_ = xmit_seqno + 1;
				npacket++;
				pipe_++;
				if (QOption_)
					process_qoption_after_send () ;
	                        if (qs_approved_ == 1) {
	                                double delay = (double) t_rtt_ * tcp_tick_ / cwnd_;
	                                delsnd_timer_.resched(delay);
	                                return;
	                        }
			}
		} else if (!(delsnd_timer_.status() == TIMER_PENDING)) {
			/*
			 * Set a delayed send timeout.
			 * This is only for the simulator,to add some
			 *   randomization if speficied.
			 */
			delsnd_timer_.resched(Random::uniform(overhead_));
			return;
		}
		if (maxburst && npacket == maxburst)
			break;
	} /* while */
}

void Sack1TcpAgent::plot()
{
#ifdef notyet
	double t = Scheduler::instance().clock();
	sprintf(trace_->buffer(), "t %g %d rtt %g\n", 
		t, class_, t_rtt_ * tcp_tick_);
	trace_->dump();
	sprintf(trace_->buffer(), "t %g %d dev %g\n", 
		t, class_, t_rttvar_ * tcp_tick_);
	trace_->dump();
	sprintf(trace_->buffer(), "t %g %d win %f\n", t, class_, cwnd_);
	trace_->dump();
	sprintf(trace_->buffer(), "t %g %d bck %d\n", t, class_, t_backoff_);
	trace_->dump();
#endif
}