tcp.cc

这个是目前国际上比较怪异的一种长距离高带宽环境下的拥塞控制算法

/* -*-  Mode:C++; c-basic-offset:8; tab-width:8; indent-tabs-mode:t -*- */
/*
 * Copyright (c) 1991-1997 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *  This product includes software developed by the Computer Systems
 *  Engineering Group at Lawrence Berkeley Laboratory.
 * 4. Neither the name of the University nor of the Laboratory may be used
 *    to endorse or promote products derived from this software without
 *    specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#ifndef lint
static const char rcsid[] =
	"@(#) $Header: /nfs/jade/vint/CVSROOT/ns-2/tcp/tcp.cc,v 1.144 2003/02/12 04:16:09 sfloyd Exp $ (LBL)";
#endif

#include <stdlib.h>
#include <math.h>
#include <sys/types.h>
#include "ip.h"
#include "tcp.h"
#include "flags.h"
#include "random.h"
#include "basetrace.h"
#include "hdr_qs.h"

int hdr_tcp::offset_;

static class TCPHeaderClass : public PacketHeaderClass {
public:
		TCPHeaderClass() : PacketHeaderClass("PacketHeader/TCP",
						 sizeof(hdr_tcp)) {
		bind_offset(&hdr_tcp::offset_);
	}
} class_tcphdr;

static class TcpClass : public TclClass {
public:
	TcpClass() : TclClass("Agent/TCP") {}
	TclObject* create(int , const char*const*) {
		return (new TcpAgent());
	}
} class_tcp;

TcpAgent::TcpAgent() : Agent(PT_TCP), 
	t_seqno_(0), t_rtt_(0), t_srtt_(0), t_rttvar_(0), 
	t_backoff_(0), ts_peer_(0), 
	rtx_timer_(this), delsnd_timer_(this), 
	burstsnd_timer_(this), 
	dupacks_(0), curseq_(0), highest_ack_(0), cwnd_(0), ssthresh_(0), 
	count_(0), fcnt_(0), rtt_active_(0), rtt_seq_(-1), rtt_ts_(0.0), 
	maxseq_(0), cong_action_(0), ecn_burst_(0), ecn_backoff_(0),
		ect_(0), lastreset_(0.0),
		restart_bugfix_(1), closed_(0), nrexmit_(0),
	first_decrease_(1), qs_requested_(0), qs_approved_(0)
{
#ifdef TCP_DELAY_BIND_ALL
#else /* ! TCP_DELAY_BIND_ALL */
	// not delay-bound because delay-bound tracevars aren't yet supported
	bind("t_seqno_", &t_seqno_);
	bind("rtt_", &t_rtt_);
	bind("srtt_", &t_srtt_);
	bind("rttvar_", &t_rttvar_);
	bind("backoff_", &t_backoff_);
	bind("dupacks_", &dupacks_);
	bind("seqno_", &curseq_);
	bind("ack_", &highest_ack_);
	bind("cwnd_", &cwnd_);
	bind("ssthresh_", &ssthresh_);
	bind("maxseq_", &maxseq_);
		bind("ndatapack_", &ndatapack_);
		bind("ndatabytes_", &ndatabytes_);
		bind("nackpack_", &nackpack_);
		bind("nrexmit_", &nrexmit_);
		bind("nrexmitpack_", &nrexmitpack_);
		bind("nrexmitbytes_", &nrexmitbytes_);
		bind("necnresponses_", &necnresponses_);
		bind("ncwndcuts_", &ncwndcuts_);
#endif /* TCP_DELAY_BIND_ALL */

}

void
TcpAgent::delay_bind_init_all()
{

		// Defaults for bound variables should be set in ns-default.tcl.
		delay_bind_init_one("window_");
		delay_bind_init_one("windowInit_");
		delay_bind_init_one("windowInitOption_");

		delay_bind_init_one("syn_");
		delay_bind_init_one("windowOption_");
		delay_bind_init_one("windowConstant_");
		delay_bind_init_one("windowThresh_");
		delay_bind_init_one("delay_growth_");
		delay_bind_init_one("overhead_");
		delay_bind_init_one("tcpTick_");
		delay_bind_init_one("ecn_");
		delay_bind_init_one("old_ecn_");
		delay_bind_init_one("eln_");
		delay_bind_init_one("eln_rxmit_thresh_");
		delay_bind_init_one("packetSize_");
		delay_bind_init_one("tcpip_base_hdr_size_");
	delay_bind_init_one("ts_option_size_");
		delay_bind_init_one("bugFix_");
	delay_bind_init_one("lessCareful_");
		delay_bind_init_one("slow_start_restart_");
		delay_bind_init_one("restart_bugfix_");
		delay_bind_init_one("timestamps_");
		delay_bind_init_one("maxburst_");
		delay_bind_init_one("maxcwnd_");
	delay_bind_init_one("numdupacks_");
	delay_bind_init_one("numdupacksFrac_");
		delay_bind_init_one("maxrto_");
	delay_bind_init_one("minrto_");
		delay_bind_init_one("srtt_init_");
		delay_bind_init_one("rttvar_init_");
		delay_bind_init_one("rtxcur_init_");
		delay_bind_init_one("T_SRTT_BITS");
		delay_bind_init_one("T_RTTVAR_BITS");
		delay_bind_init_one("rttvar_exp_");
		delay_bind_init_one("awnd_");
		delay_bind_init_one("decrease_num_");
		delay_bind_init_one("increase_num_");
	delay_bind_init_one("k_parameter_");
	delay_bind_init_one("l_parameter_");
		delay_bind_init_one("trace_all_oneline_");
		delay_bind_init_one("nam_tracevar_");

		delay_bind_init_one("QOption_");
		delay_bind_init_one("EnblRTTCtr_");
		delay_bind_init_one("control_increase_");
	delay_bind_init_one("noFastRetrans_");
	delay_bind_init_one("precisionReduce_");
	delay_bind_init_one("oldCode_");
	delay_bind_init_one("useHeaders_");
	delay_bind_init_one("low_window_");
	delay_bind_init_one("high_window_");
	delay_bind_init_one("high_p_");
	delay_bind_init_one("high_decrease_");
	delay_bind_init_one("max_ssthresh_");
	delay_bind_init_one("cwnd_frac_");
	delay_bind_init_one("timerfix_");
	delay_bind_init_one("rfc2988_");
	delay_bind_init_one("singledup_");
	delay_bind_init_one("rate_request_");
	delay_bind_init_one("qs_enabled_");

#ifdef TCP_DELAY_BIND_ALL
	// out because delay-bound tracevars aren't yet supported
		delay_bind_init_one("t_seqno_");
		delay_bind_init_one("rtt_");
		delay_bind_init_one("srtt_");
		delay_bind_init_one("rttvar_");
		delay_bind_init_one("backoff_");
		delay_bind_init_one("dupacks_");
		delay_bind_init_one("seqno_");
		delay_bind_init_one("ack_");
		delay_bind_init_one("cwnd_");
		delay_bind_init_one("ssthresh_");
		delay_bind_init_one("maxseq_");
		delay_bind_init_one("ndatapack_");
		delay_bind_init_one("ndatabytes_");
		delay_bind_init_one("nackpack_");
		delay_bind_init_one("nrexmit_");
		delay_bind_init_one("nrexmitpack_");
		delay_bind_init_one("nrexmitbytes_");
		delay_bind_init_one("necnresponses_");
		delay_bind_init_one("ncwndcuts_");
#endif /* TCP_DELAY_BIND_ALL */

	Agent::delay_bind_init_all();

		reset();
}

int
TcpAgent::delay_bind_dispatch(const char *varName, const char *localName, TclObject *tracer)
{
		if (delay_bind(varName, localName, "window_", &wnd_, tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "windowInit_", &wnd_init_, tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "windowInitOption_", &wnd_init_option_, tracer)) return TCL_OK;
		if (delay_bind_bool(varName, localName, "syn_", &syn_, tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "windowOption_", &wnd_option_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "windowConstant_",  &wnd_const_, tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "windowThresh_", &wnd_th_ , tracer)) return TCL_OK;
		if (delay_bind_bool(varName, localName, "delay_growth_", &delay_growth_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "overhead_", &overhead_, tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "tcpTick_", &tcp_tick_, tracer)) return TCL_OK;
		if (delay_bind_bool(varName, localName, "ecn_", &ecn_, tracer)) return TCL_OK;
		if (delay_bind_bool(varName, localName, "old_ecn_", &old_ecn_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "eln_", &eln_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "eln_rxmit_thresh_", &eln_rxmit_thresh_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "packetSize_", &size_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "tcpip_base_hdr_size_", &tcpip_base_hdr_size_, tracer)) return TCL_OK;
	if (delay_bind(varName, localName, "ts_option_size_", &ts_option_size_, tracer)) return TCL_OK;
		if (delay_bind_bool(varName, localName, "bugFix_", &bug_fix_ , tracer)) return TCL_OK;
		if (delay_bind_bool(varName, localName, "lessCareful_", &less_careful_ , tracer)) return TCL_OK;
		if (delay_bind_bool(varName, localName, "timestamps_", &ts_option_ , tracer)) return TCL_OK;
		if (delay_bind_bool(varName, localName, "slow_start_restart_", &slow_start_restart_ , tracer)) return TCL_OK;
		if (delay_bind_bool(varName, localName, "restart_bugfix_", &restart_bugfix_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "maxburst_", &maxburst_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "maxcwnd_", &maxcwnd_ , tracer)) return TCL_OK;
	if (delay_bind(varName, localName, "numdupacks_", &numdupacks_, tracer)) return TCL_OK;
	if (delay_bind(varName, localName, "numdupacksFrac_", &numdupacksFrac_, tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "maxrto_", &maxrto_ , tracer)) return TCL_OK;
	if (delay_bind(varName, localName, "minrto_", &minrto_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "srtt_init_", &srtt_init_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "rttvar_init_", &rttvar_init_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "rtxcur_init_", &rtxcur_init_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "T_SRTT_BITS", &T_SRTT_BITS , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "T_RTTVAR_BITS", &T_RTTVAR_BITS , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "rttvar_exp_", &rttvar_exp_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "awnd_", &awnd_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "decrease_num_", &decrease_num_, tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "increase_num_", &increase_num_, tracer)) return TCL_OK;
	if (delay_bind(varName, localName, "k_parameter_", &k_parameter_, tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "l_parameter_", &l_parameter_, tracer)) return TCL_OK;


		if (delay_bind_bool(varName, localName, "trace_all_oneline_", &trace_all_oneline_ , tracer)) return TCL_OK;
		if (delay_bind_bool(varName, localName, "nam_tracevar_", &nam_tracevar_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "QOption_", &QOption_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "EnblRTTCtr_", &EnblRTTCtr_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "control_increase_", &control_increase_ , tracer)) return TCL_OK;
		if (delay_bind_bool(varName, localName, "noFastRetrans_", &noFastRetrans_, tracer)) return TCL_OK;
		if (delay_bind_bool(varName, localName, "precisionReduce_", &precision_reduce_, tracer)) return TCL_OK;
	if (delay_bind_bool(varName, localName, "oldCode_", &oldCode_, tracer)) return TCL_OK;
	if (delay_bind_bool(varName, localName, "useHeaders_", &useHeaders_, tracer)) return TCL_OK;
	if (delay_bind(varName, localName, "low_window_", &low_window_, tracer)) return TCL_OK;
	if (delay_bind(varName, localName, "high_window_", &high_window_, tracer)) return TCL_OK;
	if (delay_bind(varName, localName, "high_p_", &high_p_, tracer)) return TCL_OK;
	if (delay_bind(varName, localName, "high_decrease_", &high_decrease_, tracer)) return TCL_OK;
	if (delay_bind(varName, localName, "max_ssthresh_", &max_ssthresh_, tracer)) return TCL_OK;
	if (delay_bind(varName, localName, "cwnd_frac_", &cwnd_frac_, tracer)) return TCL_OK;
	if (delay_bind_bool(varName, localName, "timerfix_", &timerfix_, tracer)) return TCL_OK;
	if (delay_bind_bool(varName, localName, "rfc2988_", &rfc2988_, tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "singledup_", &singledup_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "rate_request_", &rate_request_ , tracer)) return TCL_OK;
		if (delay_bind_bool(varName, localName, "qs_enabled_", &qs_enabled_, tracer)) return TCL_OK;


#ifdef TCP_DELAY_BIND_ALL
	// not if (delay-bound delay-bound tracevars aren't yet supported
		if (delay_bind(varName, localName, "t_seqno_", &t_seqno_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "rtt_", &t_rtt_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "srtt_", &t_srtt_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "rttvar_", &t_rttvar_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "backoff_", &t_backoff_ , tracer)) return TCL_OK;

		if (delay_bind(varName, localName, "dupacks_", &dupacks_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "seqno_", &curseq_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "ack_", &highest_ack_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "cwnd_", &cwnd_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "ssthresh_", &ssthresh_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "maxseq_", &maxseq_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "ndatapack_", &ndatapack_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "ndatabytes_", &ndatabytes_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "nackpack_", &nackpack_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "nrexmit_", &nrexmit_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "nrexmitpack_", &nrexmitpack_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "nrexmitbytes_", &nrexmitbytes_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "necnresponses_", &necnresponses_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "ncwndcuts_", &ncwndcuts_ , tracer)) return TCL_OK;

		if (delay_bind(varName, localName, "dl_count_", &dl_count_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "dl_minrtt_", &dl_minrtt_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "dl_maxrtt_", &dl_maxrtt_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "dl_oldmaxB_", &dl_oldmaxB_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "dl_thresh_", &dl_thresh_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "dl_Bi_", &dl_Bi_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "dl_packetcount_", &dl_packetcount_ , tracer)) return TCL_OK;
		if (delay_bind(varName, localName, "dl_rtti_", &dl_rtti_ , tracer)) return TCL_OK;

#endif

		return Agent::delay_bind_dispatch(varName, localName, tracer);
}

/* Print out all the traced variables whenever any one is changed */
void
TcpAgent::traceAll() {
	double curtime;
	Scheduler& s = Scheduler::instance();
	char wrk[500];
	int n;

	curtime = &s ? s.clock() : 0;
	sprintf(wrk,"time: %-8.5f saddr: %-2d sport: %-2d daddr: %-2d dport:"
		" %-2d maxseq: %-4d hiack: %-4d seqno: %-4d cwnd: %-6.3f"
		" ssthresh: %-3d dupacks: %-2d rtt: %-6.3f srtt: %-6.3f"
		" rttvar: %-6.3f bkoff: %-d", curtime, addr(), port(),
		daddr(), dport(), int(maxseq_), int(highest_ack_),
		int(t_seqno_), double(cwnd_), int(ssthresh_),
		int(dupacks_), int(t_rtt_)*tcp_tick_, 
		(int(t_srtt_) >> T_SRTT_BITS)*tcp_tick_, 
		int(t_rttvar_)*tcp_tick_/4.0, int(t_backoff_)); 
	n = strlen(wrk);
	wrk[n] = '\n';
	wrk[n+1] = 0;
	if (channel_)
		(void)Tcl_Write(channel_, wrk, n+1);
	wrk[n] = 0;
	return;
}

/* Print out just the variable that is modified */
void
TcpAgent::traceVar(TracedVar* v) 
{
	double curtime;
	Scheduler& s = Scheduler::instance();
	char wrk[500];
	int n;

	curtime = &s ? s.clock() : 0;
	if (!strcmp(v->name(), "cwnd_") || !strcmp(v->name(), "maxrto_")) 
		sprintf(wrk,"%-8.5f %-2d %-2d %-2d %-2d %s %-6.3f",
			curtime, addr(), port(), daddr(), dport(),
			v->name(), double(*((TracedDouble*) v))); 
	else if (!strcmp(v->name(), "minrto_")) 
		sprintf(wrk,"%-8.5f %-2d %-2d %-2d %-2d %s %-6.3f",
			curtime, addr(), port(), daddr(), dport(),
			v->name(), double(*((TracedDouble*) v))); 
	else if (!strcmp(v->name(), "rtt_"))
		sprintf(wrk,"%-8.5f %-2d %-2d %-2d %-2d %s %-6.3f",
			curtime, addr(), port(), daddr(), dport(),
			v->name(), int(*((TracedInt*) v))*tcp_tick_); 
	else if (!strcmp(v->name(), "srtt_")) 
		sprintf(wrk,"%-8.5f %-2d %-2d %-2d %-2d %s %-6.3f",
			curtime, addr(), port(), daddr(), dport(),
			v->name(), 
			(int(*((TracedInt*) v)) >> T_SRTT_BITS)*tcp_tick_); 
	else if (!strcmp(v->name(), "rttvar_"))
		sprintf(wrk,"%-8.5f %-2d %-2d %-2d %-2d %s %-6.3f",
			curtime, addr(), port(), daddr(), dport(),
			v->name(), 
			int(*((TracedInt*) v))*tcp_tick_/4.0); 
	else
		sprintf(wrk,"%-8.5f %-2d %-2d %-2d %-2d %s %d",
			curtime, addr(), port(), daddr(), dport(),
			v->name(), int(*((TracedInt*) v))); 
	n = strlen(wrk);
	wrk[n] = '\n';
	wrk[n+1] = 0;
	if (channel_)
		(void)Tcl_Write(channel_, wrk, n+1);
	wrk[n] = 0;
	return;
}

void
TcpAgent::trace(TracedVar* v) 
{
	if (nam_tracevar_) {
		Agent::trace(v);
	} else if (trace_all_oneline_)
		traceAll();
	else 
		traceVar(v);
}

//
// in 1-way TCP, syn_ indicates we are modeling
// a SYN exchange at the beginning.  If this is true
// and we are delaying growth, then use an initial
// window of one.  If not, we do whatever initial_window()
// says to do.
//

void
TcpAgent::set_initial_window()
{
	if (syn_ && delay_growth_)
		cwnd_ = 1.0; 
	else
		cwnd_ = initial_window();
}

void
TcpAgent::reset_qoption()
{
	int now = (int)(Scheduler::instance().clock()/tcp_tick_ + 0.5);

	T_start = now ; 
	RTT_count = 0 ; 
	RTT_prev = 0 ; 
	RTT_goodcount = 1 ; 
	F_counting = 0 ; 
	W_timed = -1 ; 
	F_full = 0 ;
	Backoffs = 0 ; 
}

void
TcpAgent::reset()
{
	rtt_init();
	rtt_seq_ = -1;
	/*XXX lookup variables */
	dupacks_ = 0;
	curseq_ = 0;
	set_initial_window();

	t_seqno_ = 0;
	maxseq_ = -1;
	last_ack_ = -1;
	highest_ack_ = -1;
	ssthresh_ = int(wnd_);
	if (max_ssthresh_ > 0 && max_ssthresh_ < ssthresh_) 
		ssthresh_ = max_ssthresh_;
	wnd_restart_ = 1.;
	awnd_ = wnd_init_ / 2.0;
	recover_ = 0;
	closed_ = 0;
	last_cwnd_action_ = 0;
	boot_time_ = Random::uniform(tcp_tick_);
	first_decrease_ = 1;
	
	dl_rtti_=0; dl_minrtt_=10000; dl_maxrtt_=0; 
	dl_modecount_=0; dl_count_=0;  dl_mode_=1; dl_alpha_=0;
	dl_thresh_=0; dl_packetcount_=0; dl_Bi_=0; dl_maxB_=0; dl_oldmaxB_=0; dl_minB_=0;
				
	/* W.N.: for removing packets from previous incarnations */
	lastreset_ = Scheduler::instance().clock();

	/* Now these variables will be reset 
	   - Debojyoti Dutta 12th Oct'2000 */
 
	ndatapack_ = 0;
	ndatabytes_ = 0;
	nackpack_ = 0;
	nrexmitbytes_ = 0;
	nrexmit_ = 0;
	nrexmitpack_ = 0;
	necnresponses_ = 0;
	ncwndcuts_ = 0;

		cwnd_last_ = 0.0;

	if (control_increase_) {
		prev_highest_ack_ = highest_ack_ ; 
	}

	if (QOption_) {
		int now = (int)(Scheduler::instance().clock()/tcp_tick_ + 0.5);
		T_last = now ; 
		T_prev = now ; 
		W_used = 0 ;
		if (EnblRTTCtr_) {
			reset_qoption();
		}
	}
}

/*
 * Initialize variables for the retransmit timer.
 */
void TcpAgent::rtt_init()
{
	t_rtt_ = 0;
	t_srtt_ = int(srtt_init_ / tcp_tick_) << T_SRTT_BITS;
	t_rttvar_ = int(rttvar_init_ / tcp_tick_) << T_RTTVAR_BITS;
	t_rtxcur_ = rtxcur_init_;
	t_backoff_ = 1;
}