tcp.cc

Go to the documentation of this file.

/* -*-  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 1.163 2005/06/21 01:48:24 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), ts_echo_(0),
      tss(NULL), tss_size_(100), 
      rtx_timer_(this), delsnd_timer_(this), burstsnd_timer_(this), 
      dupacks_(0), curseq_(0), highest_ack_(0), cwnd_(0), ssthresh_(0), 
      maxseq_(0), count_(0), rtt_active_(0), rtt_seq_(-1), rtt_ts_(0.0), 
      lastreset_(0.0), closed_(0), first_decrease_(1), fcnt_(0), 
      nrexmit_(0), restart_bugfix_(1), cong_action_(0), 
      ecn_burst_(0), ecn_backoff_(0), ect_(0), 
      qs_requested_(0), qs_approved_(0),
      qs_window_(0), qs_cwnd_(0), frto_(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_);
    bind("ncwndcuts1_", &ncwndcuts1_);
#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("SetCWRonRetransmit_");
        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("bugFix_ack_");
    delay_bind_init_one("bugFix_ts_");
    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("ts_resetRTO_");
        delay_bind_init_one("maxburst_");
    delay_bind_init_one("aggressive_maxburst_");
        delay_bind_init_one("maxcwnd_");
    delay_bind_init_one("numdupacks_");
    delay_bind_init_one("numdupacksFrac_");
    delay_bind_init_one("exitFastRetrans_");
        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_range_");
    delay_bind_init_one("timerfix_");
    delay_bind_init_one("rfc2988_");
    delay_bind_init_one("singledup_");
    delay_bind_init_one("LimTransmitFix_");
    delay_bind_init_one("rate_request_");
    delay_bind_init_one("qs_enabled_");
    delay_bind_init_one("tcp_qs_recovery_");
    delay_bind_init_one("qs_request_mode_");
    delay_bind_init_one("qs_thresh_");
    delay_bind_init_one("qs_rtt_");

    delay_bind_init_one("frto_enabled_");
    delay_bind_init_one("sfrto_enabled_");
    delay_bind_init_one("spurious_response_");

#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_");
    delay_bind_init_one("ncwndcuts1_");
#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, "SetCWRonRetransmit_", &SetCWRonRetransmit_, 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, "bugFix_ack_", &bugfix_ack_, tracer)) return TCL_OK;
    if (delay_bind_bool(varName, localName, "bugFix_ts_", &bugfix_ts_ , 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, "ts_resetRTO_", &ts_resetRTO_, 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_bool(varName, localName, "aggressive_maxburst_", &aggressive_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_bool(varName, localName, "exitFastRetrans_", &exitFastRetrans_, 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_range_", &cwnd_range_, 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_bool(varName, localName, "LimTransmitFix_", &LimTransmitFix_ , 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;
    if (delay_bind_bool(varName, localName, "tcp_qs_recovery_", &tcp_qs_recovery_, tracer)) return TCL_OK;

    if (delay_bind_bool(varName, localName, "frto_enabled_", &frto_enabled_, tracer)) return TCL_OK;
    if (delay_bind_bool(varName, localName, "sfrto_enabled_", &sfrto_enabled_, tracer)) return TCL_OK;
    if (delay_bind_bool(varName, localName, "spurious_response_", &spurious_response_, 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, "ncwndcuts1_", &ncwndcuts1_ , tracer)) return TCL_OK;

#endif

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

#define TCP_WRK_SIZE        512
/* Print out all the traced variables whenever any one is changed */
void
TcpAgent::traceAll() {
    if (!channel_)
        return;

    double curtime;
    Scheduler& s = Scheduler::instance();
    char wrk[TCP_WRK_SIZE];

    curtime = &s ? s.clock() : 0;
    snprintf(wrk, TCP_WRK_SIZE,
         "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\n", 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_)); 
    (void)Tcl_Write(channel_, wrk, -1);
}

/* Print out just the variable that is modified */
void
TcpAgent::traceVar(TracedVar* v) 
{
    if (!channel_)
        return;

    double curtime;
    Scheduler& s = Scheduler::instance();
    char wrk[TCP_WRK_SIZE];

    curtime = &s ? s.clock() : 0;

    // XXX comparing addresses is faster than comparing names
    if (v == &cwnd_)
        snprintf(wrk, TCP_WRK_SIZE,
             "%-8.5f %-2d %-2d %-2d %-2d %s %-6.3f\n",
             curtime, addr(), port(), daddr(), dport(),
             v->name(), double(*((TracedDouble*) v))); 
    else if (v == &t_rtt_)
        snprintf(wrk, TCP_WRK_SIZE,
             "%-8.5f %-2d %-2d %-2d %-2d %s %-6.3f\n",
             curtime, addr(), port(), daddr(), dport(),
             v->name(), int(*((TracedInt*) v))*tcp_tick_); 
    else if (v == &t_srtt_)
        snprintf(wrk, TCP_WRK_SIZE,
             "%-8.5f %-2d %-2d %-2d %-2d %s %-6.3f\n",
             curtime, addr(), port(), daddr(), dport(),
             v->name(), 
             (int(*((TracedInt*) v)) >> T_SRTT_BITS)*tcp_tick_); 
    else if (v == &t_rttvar_)
        snprintf(wrk, TCP_WRK_SIZE,
             "%-8.5f %-2d %-2d %-2d %-2d %s %-6.3f\n",
             curtime, addr(), port(), daddr(), dport(),
             v->name(), 
             int(*((TracedInt*) v))*tcp_tick_/4.0); 
    else
        snprintf(wrk, TCP_WRK_SIZE,
             "%-8.5f %-2d %-2d %-2d %-2d %s %d\n",
             curtime, addr(), port(), daddr(), dport(),
             v->name(), int(*((TracedInt*) v))); 

    (void)Tcl_Write(channel_, wrk, -1);
}

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;
    /* 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;
    ncwndcuts1_ = 0;

    if (control_increase_) {
        prev_highest_ack_ = highest_ack_ ; 
    }

    if (wnd_option_ == 8) {
        // HighSpeed TCP
        hstcp_.low_p = 1.5/(low_window_*low_window_);
        double highLowWin = log(high_window_)-log(low_window_);
        double highLowP = log(high_p_) - log(hstcp_.low_p);
        hstcp_.dec1 = 
           0.5 - log(low_window_) * (high_decrease_ - 0.5)/highLowWin;
        hstcp_.dec2 = (high_decrease_ - 0.5)/highLowWin;
            hstcp_.p1 = 
          log(hstcp_.low_p) - log(low_window_) * highLowP/highLowWin;
        hstcp_.p2 = highLowP/highLowWin;
    }

    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;
}

double TcpAgent::rtt_timeout()
{
    double timeout;
    if (rfc2988_) {
    // Correction from Tom Kelly to be RFC2988-compliant, by
    // clamping minrto_ before applying t_backoff_.
        if (t_rtxcur_ < minrto_)
            timeout = minrto_ * t_backoff_;
        else
            timeout = t_rtxcur_ * t_backoff_;
    } else {
        timeout = t_rtxcur_ * t_backoff_;
        if (timeout < minrto_)
            timeout = minrto_;
    }

    if (timeout > maxrto_)
        timeout = maxrto_;

        if (timeout < 2.0 * tcp_tick_) {
        if (timeout < 0) {
            fprintf(stderr, "TcpAgent: negative RTO!  (%f)\n",
                timeout);
            exit(1);
        }
        timeout = 2.0 * tcp_tick_;
    }
    return (timeout);
}


/* This has been modified to use the tahoe code. */
void TcpAgent::rtt_update(double tao)
{
    double now = Scheduler::instance().clock();
    if (ts_option_)
        t_rtt_ = int(tao /tcp_tick_ + 0.5);
    else {
        double sendtime = now - tao;
        sendtime += boot_time_;
        double tickoff = fmod(sendtime, tcp_tick_);
        t_rtt_ = int((tao + tickoff) / tcp_tick_);
    }
    if (t_rtt_ < 1)
        t_rtt_ = 1;
    //
    // t_srtt_ has 3 bits to the right of the binary point
    // t_rttvar_ has 2
        // Thus "t_srtt_ >> T_SRTT_BITS" is the actual srtt, 
    //   and "t_srtt_" is 8*srtt.
    // Similarly, "t_rttvar_ >> T_RTTVAR_BITS" is the actual rttvar,
    //   and "t_rttvar_" is 4*rttvar.
    //
        if (t_srtt_ != 0) {
        register short delta;
        delta = t_rtt_ - (t_srtt_ >> T_SRTT_BITS);  // d = (m - a0)
        if ((t_srtt_ += delta) <= 0)    // a1 = 7/8 a0 + 1/8 m
            t_srtt_ = 1;
        if (delta < 0)
            delta = -delta;
        delta -= (t_rttvar_ >> T_RTTVAR_BITS);
        if ((t_rttvar_ += delta) <= 0)  // var1 = 3/4 var0 + 1/4 |d|
            t_rttvar_ = 1;
    } else {
        t_srtt_ = t_rtt_ << T_SRTT_BITS;        // srtt = rtt
        t_rttvar_ = t_rtt_ << (T_RTTVAR_BITS-1);    // rttvar = rtt / 2
    }
    //
    // Current retransmit value is 
    //    (unscaled) smoothed round trip estimate
    //    plus 2^rttvar_exp_ times (unscaled) rttvar. 
    //
    t_rtxcur_ = (((t_rttvar_ << (rttvar_exp_ + (T_SRTT_BITS - T_RTTVAR_BITS))) +
        t_srtt_)  >> T_SRTT_BITS ) * tcp_tick_;

    return;
}

void TcpAgent::rtt_backoff()
{
    if (t_backoff_ < 64)
        t_backoff_ <<= 1;

    if (t_backoff_ > 8) {
        /*
         * If backed off this far, clobber the srtt
         * value, storing it in the mean deviation
         * instead.
         */
        t_rttvar_ += (t_srtt_ >> T_SRTT_BITS);
        t_srtt_ = 0;
    }
}

/*
 * headersize:
 *      how big is an IP+TCP header in bytes; include options such as ts
 * this function should be virtual so others (e.g. SACK) can override
 */
int TcpAgent::headersize()
{
        int total = tcpip_base_hdr_size_;
    if (total < 1) {
        fprintf(stderr,
          "TcpAgent(%s): warning: tcpip hdr size is only %d bytes\n",
          name(), tcpip_base_hdr_size_);
    }
    if (ts_option_)
        total += ts_option_size_;
        return (total);
}

void TcpAgent::output(int seqno, int reason)
{
    int force_set_rtx_timer = 0;
    Packet* p = allocpkt();
    hdr_tcp *tcph = hdr_tcp::access(p);
    hdr_flags* hf = hdr_flags::access(p);
    hdr_ip *iph = hdr_ip::access(p);
    int databytes = hdr_cmn::access(p)->size();
    tcph->seqno() = seqno;
    tcph->ts() = Scheduler::instance().clock();
    int is_retransmit = (seqno < maxseq_);
 
    // Mark packet for diagnosis purposes if we are in Quick-Start Phase
    if (qs_approved_) {
        hf->qs() = 1;
    }
 
        // store timestamps, with bugfix_ts_.  From Andrei Gurtov. 
    // (A real TCP would use scoreboard for this.)
        if (bugfix_ts_ && tss==NULL) {
                tss = (double*) calloc(tss_size_, sizeof(double));
                if (tss==NULL) exit(1);
        }
        //dynamically grow the timestamp array if it's getting full
        if (bugfix_ts_ && window() > tss_size_* 0.9) {
                double *ntss;
                ntss = (double*) calloc(tss_size_*2, sizeof(double));
                printf("resizing timestamp table\n");
                if (ntss == NULL) exit(1);
                for (int i=0; i<tss_size_; i++)
                        ntss[(highest_ack_ + i) % (tss_size_ * 2)] =
                                tss[(highest_ack_ + i) % tss_size_];
                free(tss);
                tss_size_ *= 2;
                tss = ntss;
        }
 
        if (tss!=NULL)
                tss[seqno % tss_size_] = tcph->ts(); 

    tcph->ts_echo() = ts_peer_;
    tcph->reason() = reason;
    tcph->last_rtt() = int(int(t_rtt_)*tcp_tick_*1000);

    if (ecn_) {
        hf->ect() = 1;  // ECN-capable transport
    }
    if (cong_action_ && (!is_retransmit || SetCWRonRetransmit_)) {
        hf->cong_action() = TRUE;  // Congestion action.
        cong_action_ = FALSE;
        }
    /* Check if this is the initial SYN packet. */
    if (seqno == 0) {
        if (syn_) {
            databytes = 0;
            curseq_ += 1;
            hdr_cmn::access(p)->size() = tcpip_base_hdr_size_;
        }
        if (ecn_) {
            hf->ecnecho() = 1;
//          hf->cong_action() = 1;
            hf->ect() = 0;
        }
        if (qs_enabled_) {
            hdr_qs *qsh = hdr_qs::access(p);

            // dataout is kilobytes queued for sending
            int dataout = (curseq_ - maxseq_ - 1) * (size_ + headersize()) / 1024;
            int qs_rr = rate_request_;
            if (qs_request_mode_ == 1) {
                // PS: Avoid making unnecessary QS requests
                // use a rough estimation of RTT in qs_rtt_
                // to calculate the desired rate from dataout.
                if (dataout * 1000 / qs_rtt_ < qs_rr) {
                    qs_rr = dataout * 1000 / qs_rtt_;
                }
                // qs_thresh_ is minimum number of unsent
                // segments needed to activate QS request
                if ((curseq_ - maxseq_ - 1) < qs_thresh_) {
                    qs_rr = 0;
                }
            }

                if (qs_rr > 0) {
                // QuickStart code from Srikanth Sundarrajan.
                qsh->flag() = QS_REQUEST;
                qsh->ttl() = Random::integer(256);
                ttl_diff_ = (iph->ttl() - qsh->ttl()) % 256;
                qsh->rate() = hdr_qs::Bps_to_rate(qs_rr * 1024);
                qs_requested_ = 1;
                } else {
                qsh->flag() = QS_DISABLE;
            }
        }
    }
    else if (useHeaders_ == true) {
        hdr_cmn::access(p)->size() += headersize();
    }
        hdr_cmn::access(p)->size();

    /* if no outstanding data, be sure to set rtx timer again */
    if (highest_ack_ == maxseq_)
        force_set_rtx_timer = 1;
    /* call helper function to fill in additional fields */
    output_helper(p);

        ++ndatapack_;
        ndatabytes_ += databytes;
    send(p, 0);
    if (seqno == curseq_ && seqno > maxseq_)
        idle();  // Tell application I have sent everything so far
    if (seqno > maxseq_) {
        maxseq_ = seqno;
        if (!rtt_active_) {
            rtt_active_ = 1;
            if (seqno > rtt_seq_) {
                rtt_seq_ = seqno;
                rtt_ts_ = Scheduler::instance().clock();
            }
                    
        }
    } else {
            ++nrexmitpack_;
        nrexmitbytes_ += databytes;
    }
    if (!(rtx_timer_.status() == TIMER_PENDING) || force_set_rtx_timer)
        /* No timer pending.  Schedule one. */
        set_rtx_timer();
}

/*
 * Must convert bytes into packets for one-way TCPs.
 * If nbytes == -1, this corresponds to infinite send.  We approximate
 * infinite by a very large number (TCP_MAXSEQ).
 */
void TcpAgent::sendmsg(int nbytes, const char* /*flags*/)
{
    if (nbytes == -1 && curseq_ <= TCP_MAXSEQ)
        curseq_ = TCP_MAXSEQ; 
    else
        curseq_ += (nbytes/size_ + (nbytes%size_ ? 1 : 0));
    send_much(0, 0, maxburst_);
}

void TcpAgent::advanceby(int delta)
{
  curseq_ += delta;
    if (delta > 0)
        closed_ = 0;
    send_much(0, 0, maxburst_); 
}


int TcpAgent::command(int argc, const char*const* argv)
{
    if (argc == 3) {
        if (strcmp(argv[1], "advance") == 0) {
            int newseq = atoi(argv[2]);
            if (newseq > maxseq_)
                advanceby(newseq - curseq_);
            else
                advanceby(maxseq_ - curseq_);
            return (TCL_OK);
        }
        if (strcmp(argv[1], "advanceby") == 0) {
            advanceby(atoi(argv[2]));
            return (TCL_OK);
        }
        if (strcmp(argv[1], "eventtrace") == 0) {
            et_ = (EventTrace *)TclObject::lookup(argv[2]);
            return (TCL_OK);
        }
        /*
         * Curtis Villamizar's trick to transfer tcp connection
         * parameters to emulate http persistent connections.
         *
         * Another way to do the same thing is to open one tcp
         * object and use start/stop/maxpkts_ or advanceby to control
         * how much data is sent in each burst.
         * With a single connection, slow_start_restart_
         * should be configured as desired.
         *
         * This implementation (persist) may not correctly
         * emulate pure-BSD-based systems which close cwnd
         * after the connection goes idle (slow-start
         * restart).  See appendix C in
         * Jacobson and Karels ``Congestion
         * Avoidance and Control'' at
         * <ftp://ftp.ee.lbl.gov/papers/congavoid.ps.Z>
         * (*not* the original
         * '88 paper) for why BSD does this.  See
         * ``Performance Interactions Between P-HTTP and TCP
         * Implementations'' in CCR 27(2) for descriptions of
         * what other systems do the same.
         *
         */
        if (strcmp(argv[1], "persist") == 0) {
            TcpAgent *other
              = (TcpAgent*)TclObject::lookup(argv[2]);
            cwnd_ = other->cwnd_;
            awnd_ = other->awnd_;
            ssthresh_ = other->ssthresh_;
            t_rtt_ = other->t_rtt_;
            t_srtt_ = other->t_srtt_;
            t_rttvar_ = other->t_rttvar_;
            t_backoff_ = other->t_backoff_;
            return (TCL_OK);
        }
    }
    return (Agent::command(argc, argv));
}

/*
 * Returns the window size adjusted to allow <num> segments past recovery
 * point to be transmitted on next ack.
 */
int TcpAgent::force_wnd(int num)
{
    return recover_ + num - (int)highest_ack_;
}

int TcpAgent::window()
{
        /*
         * If F-RTO is enabled and first ack has come in, temporarily open
         * window for sending two segments.
     * The F-RTO code is from Pasi Sarolahti.  F-RTO is an algorithm
     * for detecting spurious retransmission timeouts.
         */
        if (frto_ == 2) {
                return (force_wnd(2) < wnd_ ?
                        force_wnd(2) : (int)wnd_);
        } else {
        return (cwnd_ < wnd_ ? (int)cwnd_ : (int)wnd_);
        }
}

double TcpAgent::windowd()
{
    return (cwnd_ < wnd_ ? (double)cwnd_ : (double)wnd_);
}

/*
 * Try to send as much data as the window will allow.  The link layer will 
 * do the buffering; we ask the application layer for the size of the packets.
 */
void TcpAgent::send_much(int force, int reason, int maxburst)
{
    send_idle_helper();
    int win = window();
    int npackets = 0;

    if (!force && delsnd_timer_.status() == TIMER_PENDING)
        return;
    /* Save time when first packet was sent, for newreno  --Allman */
    if (t_seqno_ == 0)
        firstsent_ = Scheduler::instance().clock();

    if (burstsnd_timer_.status() == TIMER_PENDING)
        return;
    while (t_seqno_ <= highest_ack_ + win && t_seqno_ < curseq_) {
        if (overhead_ == 0 || force || qs_approved_) {
            output(t_seqno_, reason);
            npackets++;
            if (QOption_)
                process_qoption_after_send () ; 
            t_seqno_ ++ ;
            if (qs_approved_ == 1) {
                // delay = effective RTT / window
                double delay = (double) t_rtt_ * tcp_tick_ / win;
                if (overhead_) { 
                    delsnd_timer_.resched(delay + Random::uniform(overhead_));
                } else {
                    delsnd_timer_.resched(delay);
                }
                return;
            }
        } else if (!(delsnd_timer_.status() == TIMER_PENDING)) {
            /*
             * Set a delayed send timeout.
             */
            delsnd_timer_.resched(Random::uniform(overhead_));
            return;
        }
        win = window();
        if (maxburst && npackets == maxburst)
            break;
    }
    /* call helper function */
    send_helper(maxburst);
}

/*
 * We got a timeout or too many duplicate acks.  Clear the retransmit timer.  
 * Resume the sequence one past the last packet acked.  
 * "mild" is 0 for timeouts and Tahoe dup acks, 1 for Reno dup acks.
 * "backoff" is 1 if the timer should be backed off, 0 otherwise.
 */
void TcpAgent::reset_rtx_timer(int mild, int backoff)
{
    if (backoff)
        rtt_backoff();
    set_rtx_timer();
    if (!mild)
        t_seqno_ = highest_ack_ + 1;
    rtt_active_ = 0;
}

/*
 * Set retransmit timer using current rtt estimate.  By calling resched(), 
 * it does not matter whether the timer was already running.
 */
void TcpAgent::set_rtx_timer()
{
    rtx_timer_.resched(rtt_timeout());
}

/*
 * Set new retransmission timer if not all outstanding
 * or available data acked, or if we are unable to send because 
 * cwnd is less than one (as when the ECN bit is set when cwnd was 1).
 * Otherwise, if a timer is still outstanding, cancel it.
 */
void TcpAgent::newtimer(Packet* pkt)
{
    hdr_tcp *tcph = hdr_tcp::access(pkt);
    /*
     * t_seqno_, the next packet to send, is reset (decreased) 
     *   to highest_ack_ + 1 after a timeout,
     *   so we also have to check maxseq_, the highest seqno sent.
     * In addition, if the packet sent after the timeout has
     *   the ECN bit set, then the returning ACK caused cwnd_ to
     *   be decreased to less than one, and we can't send another
     *   packet until the retransmit timer again expires.
     *   So we have to check for "cwnd_ < 1" as well.
     */
    if (t_seqno_ > tcph->seqno() || tcph->seqno() < maxseq_ || cwnd_ < 1) 
        set_rtx_timer();
    else
        cancel_rtx_timer();
}

/*
 * for experimental, high-speed TCP
 */
double TcpAgent::linear(double x, double x_1, double y_1, double x_2, double y_2)
{
    // The y coordinate factor ranges from y_1 to y_2
    //  as the x coordinate ranges from x_1 to x_2.
    double y = y_1 + ((y_2 - y_1) * ((x - x_1)/(x_2-x_1)));
    return y;
}

/*
 * Limited Slow-Start for large congestion windows.
 * This is only used when max_ssthresh_ is non-zero.
 */
double TcpAgent::limited_slow_start(double cwnd, double max_ssthresh, double increment)
{
    int round = int(cwnd / (double(max_ssthresh)/2.0));
    double increment1 = 1.0/(double(round)); 
    if (increment < increment1)
        increment = increment1;
    return increment;
}

/*
 * For retrieving numdupacks_.
 */
int TcpAgent::numdupacks(double cwnd)
{
        int cwndfraction = (int) cwnd/numdupacksFrac_;
    if (numdupacks_ > cwndfraction) {
        return numdupacks_;
        } else {
        return cwndfraction;
    }
}

/*
 * Calculating the decrease parameter for highspeed TCP.
 */
double TcpAgent::decrease_param()
{
    double decrease;
    // OLD:
    // decrease = linear(log(cwnd_), log(low_window_), 0.5, log(high_window_), high_decrease_);
    // NEW (but equivalent):
        decrease = hstcp_.dec1 + log(cwnd_) * hstcp_.dec2;  
    return decrease;
}

/*
 * Calculating the increase parameter for highspeed TCP.
 */
double TcpAgent::increase_param()
{
    double increase, decrease, p, answer;
    /* extending the slow-start for high-speed TCP */

    /* for highspeed TCP -- from Sylvia Ratnasamy, */
    /* modifications by Sally Floyd and Evandro de Souza */
    // p ranges from 1.5/W^2 at congestion window low_window_, to
    //    high_p_ at congestion window high_window_, on a log-log scale.
        // The decrease factor ranges from 0.5 to high_decrease
    //  as the window ranges from low_window to high_window, 
    //  as the log of the window. 
    // For an efficient implementation, this would just be looked up
    //   in a table, with the increase and decrease being a function of the
    //   congestion window.

       if (cwnd_ <= low_window_) { 
        answer = 1 / cwnd_;
            return answer; 
       } else if (cwnd_ >= hstcp_.cwnd_last_ && 
          cwnd_ < hstcp_.cwnd_last_ + cwnd_range_) {
          // cwnd_range_ can be set to 0 to be disabled,
          //  or can be set from 1 to 100 
            answer = hstcp_.increase_last_ / cwnd_;
                return answer;
       } else { 
        // OLD:
        // p = exp(linear(log(cwnd_), log(low_window_), log(hstcp_.low_p), log(high_window_), log(high_p_)));
        // NEW, but equivalent:
            p = exp(hstcp_.p1 + log(cwnd_) * hstcp_.p2);  
            decrease = decrease_param();
        // OLD:
        // increase = cwnd_*cwnd_*p *(2.0*decrease)/(2.0 - decrease); 
        // NEW, but equivalent:
        increase = cwnd_ * cwnd_ * p /(1/decrease - 0.5);
        //  if (increase > max_increase) { 
        //      increase = max_increase;
        //  } 
        answer = increase / cwnd_;
        hstcp_.cwnd_last_ = cwnd_;
        hstcp_.increase_last_ = increase;
            return answer;
    }       
}

/*
 * open up the congestion window
 */
void TcpAgent::opencwnd()
{
    double increment;
    if (cwnd_ < ssthresh_) {
        /* slow-start (exponential) */
        cwnd_ += 1;
    } else {
        /* linear */
        double f;
        switch (wnd_option_) {
        case 0:
            if (++count_ >= cwnd_) {
                count_ = 0;
                ++cwnd_;
            }
            break;

        case 1:
            /* This is the standard algorithm. */
            increment = increase_num_ / cwnd_;
            if ((last_cwnd_action_ == 0 ||
              last_cwnd_action_ == CWND_ACTION_TIMEOUT) 
              && max_ssthresh_ > 0) {
                increment = limited_slow_start(cwnd_,
                  max_ssthresh_, increment);
            }
            cwnd_ += increment;
            break;

        case 2:
            /* These are window increase algorithms
             * for experimental purposes only. */
            /* This is the Constant-Rate increase algorithm 
                         *  from the 1991 paper by S. Floyd on "Connections  
             *  with Multiple Congested Gateways". 
             *  The window is increased by roughly 
             *  wnd_const_*RTT^2 packets per round-trip time.  */
            f = (t_srtt_ >> T_SRTT_BITS) * tcp_tick_;
            f *= f;
            f *= wnd_const_;
            /* f = wnd_const_ * RTT^2 */
            f += fcnt_;
            if (f > cwnd_) {
                fcnt_ = 0;
                ++cwnd_;
            } else
                fcnt_ = f;
            break;

        case 3:
            /* The window is increased by roughly 
             *  awnd_^2 * wnd_const_ packets per RTT,
             *  for awnd_ the average congestion window. */
            f = awnd_;
            f *= f;
            f *= wnd_const_;
            f += fcnt_;
            if (f > cwnd_) {
                fcnt_ = 0;
                ++cwnd_;
            } else
                fcnt_ = f;
            break;

                case 4:
            /* The window is increased by roughly 
             *  awnd_ * wnd_const_ packets per RTT,
             *  for awnd_ the average congestion window. */
                        f = awnd_;
                        f *= wnd_const_;
                        f += fcnt_;
                        if (f > cwnd_) {
                                fcnt_ = 0;
                                ++cwnd_;
                        } else
                                fcnt_ = f;
                        break;
        case 5:
            /* The window is increased by roughly wnd_const_*RTT 
             *  packets per round-trip time, as discussed in
             *  the 1992 paper by S. Floyd on "On Traffic 
             *  Phase Effects in Packet-Switched Gateways". */
                        f = (t_srtt_ >> T_SRTT_BITS) * tcp_tick_;
                        f *= wnd_const_;
                        f += fcnt_;
                        if (f > cwnd_) {
                                fcnt_ = 0;
                                ++cwnd_;
                        } else
                                fcnt_ = f;
                        break;
                case 6:
                        /* binomial controls */ 
                        cwnd_ += increase_num_ / (cwnd_*pow(cwnd_,k_parameter_));                
                        break; 
        case 8: 
            /* high-speed TCP, RFC 3649 */
            increment = increase_param();
            if ((last_cwnd_action_ == 0 ||
              last_cwnd_action_ == CWND_ACTION_TIMEOUT) 
              && max_ssthresh_ > 0) {
                increment = limited_slow_start(cwnd_,
                  max_ssthresh_, increment);
            }
            cwnd_ += increment;
                        break;
        default:
#ifdef notdef
            /*XXX*/
            error("illegal window option %d", wnd_option_);
#endif
            abort();
        }
    }
    // if maxcwnd_ is set (nonzero), make it the cwnd limit
    if (maxcwnd_ && (int(cwnd_) > maxcwnd_))
        cwnd_ = maxcwnd_;

    return;
}

void
TcpAgent::slowdown(int how)
{
    double decrease;  /* added for highspeed - sylvia */
    double win, halfwin, decreasewin;
    int slowstart = 0;
    ++ncwndcuts_;
    if (!(how & TCP_IDLE) && !(how & NO_OUTSTANDING_DATA)){
        ++ncwndcuts1_; 
    }
    // we are in slowstart for sure if cwnd < ssthresh
    if (cwnd_ < ssthresh_) 
        slowstart = 1;
        if (precision_reduce_) {
        halfwin = windowd() / 2;
                if (wnd_option_ == 6) {         
                        /* binomial controls */
                        decreasewin = windowd() - (1.0-decrease_num_)*pow(windowd(),l_parameter_);
                } else if (wnd_option_ == 8 && (cwnd_ > low_window_)) { 
                        /* experimental highspeed TCP */
            decrease = decrease_param();
            //if (decrease < 0.1) 
            //  decrease = 0.1;
            decrease_num_ = decrease;
                        decreasewin = windowd() - (decrease * windowd());
                } else {
            decreasewin = decrease_num_ * windowd();
        }
        win = windowd();
    } else  {
        int temp;
        temp = (int)(window() / 2);
        halfwin = (double) temp;
                if (wnd_option_ == 6) {
                        /* binomial controls */
                        temp = (int)(window() - (1.0-decrease_num_)*pow(window(),l_parameter_));
                } else if ((wnd_option_ == 8) && (cwnd_ > low_window_)) { 
                        /* experimental highspeed TCP */
            decrease = decrease_param();
            //if (decrease < 0.1)
                        //       decrease = 0.1;        
            decrease_num_ = decrease;
                        temp = (int)(windowd() - (decrease * windowd()));
                } else {
            temp = (int)(decrease_num_ * window());
        }
        decreasewin = (double) temp;
        win = (double) window();
    }
    if (how & CLOSE_SSTHRESH_HALF)
        // For the first decrease, decrease by half
        // even for non-standard values of decrease_num_.
        if (first_decrease_ == 1 || slowstart ||
            last_cwnd_action_ == CWND_ACTION_TIMEOUT) {
            // Do we really want halfwin instead of decreasewin
        // after a timeout?
            ssthresh_ = (int) halfwin;
        } else {
            ssthresh_ = (int) decreasewin;
        }
        else if (how & THREE_QUARTER_SSTHRESH)
        if (ssthresh_ < 3*cwnd_/4)
            ssthresh_  = (int)(3*cwnd_/4);
    if (how & CLOSE_CWND_HALF)
        // For the first decrease, decrease by half
        // even for non-standard values of decrease_num_.
        if (first_decrease_ == 1 || slowstart || decrease_num_ == 0.5) {
            cwnd_ = halfwin;
        } else cwnd_ = decreasewin;
        else if (how & CWND_HALF_WITH_MIN) {
        // We have not thought about how non-standard TCPs, with
        // non-standard values of decrease_num_, should respond
        // after quiescent periods.
                cwnd_ = decreasewin;
                if (cwnd_ < 1)
                        cwnd_ = 1;
    }
    else if (how & CLOSE_CWND_RESTART) 
        cwnd_ = int(wnd_restart_);
    else if (how & CLOSE_CWND_INIT)
        cwnd_ = int(wnd_init_);
    else if (how & CLOSE_CWND_ONE)
        cwnd_ = 1;
    else if (how & CLOSE_CWND_HALF_WAY) {
        // cwnd_ = win - (win - W_used)/2 ;
        cwnd_ = W_used + decrease_num_ * (win - W_used);
                if (cwnd_ < 1)
                        cwnd_ = 1;
    }
    if (ssthresh_ < 2)
        ssthresh_ = 2;
    if (how & (CLOSE_CWND_HALF|CLOSE_CWND_RESTART|CLOSE_CWND_INIT|CLOSE_CWND_ONE))
        cong_action_ = TRUE;

    fcnt_ = count_ = 0;
    if (first_decrease_ == 1)
        first_decrease_ = 0;
    // for event tracing slow start
    if (cwnd_ == 1 || slowstart) 
        // Not sure if this is best way to capture slow_start
        // This is probably tracing a superset of slowdowns of
        // which all may not be slow_start's --Padma, 07/'01.
        trace_event("SLOW_START");
    


    
}

/*
 * Process a packet that acks previously unacknowleged data.
 */
void TcpAgent::newack(Packet* pkt)
{
    double now = Scheduler::instance().clock();
    hdr_tcp *tcph = hdr_tcp::access(pkt);
    /* 
     * Wouldn't it be better to set the timer *after*
     * updating the RTT, instead of *before*? 
     */
    if (!timerfix_) newtimer(pkt);
    dupacks_ = 0;
    last_ack_ = tcph->seqno();
    prev_highest_ack_ = highest_ack_ ;
    highest_ack_ = last_ack_;

    if (t_seqno_ < last_ack_ + 1)
        t_seqno_ = last_ack_ + 1;
    /* 
     * Update RTT only if it's OK to do so from info in the flags header.
     * This is needed for protocols in which intermediate agents
     * in the network intersperse acks (e.g., ack-reconstructors) for
     * various reasons (without violating e2e semantics).
     */ 
    hdr_flags *fh = hdr_flags::access(pkt);
    if (!fh->no_ts_) {
        if (ts_option_) {
            ts_echo_=tcph->ts_echo();
            rtt_update(now - tcph->ts_echo());
            if (ts_resetRTO_ && (!ect_ || !ecn_backoff_ ||
                !hdr_flags::access(pkt)->ecnecho())) { 
                // From Andrei Gurtov
                /* 
                 * Don't end backoff if still in ECN-Echo with
                 * a congestion window of 1 packet. 
                 */
                t_backoff_ = 1;
                ecn_backoff_ = 0;
            }
        }
        if (rtt_active_ && tcph->seqno() >= rtt_seq_) {
            if (!ect_ || !ecn_backoff_ || 
                !hdr_flags::access(pkt)->ecnecho()) {
                /* 
                 * Don't end backoff if still in ECN-Echo with
                 * a congestion window of 1 packet. 
                 */
                t_backoff_ = 1;
                ecn_backoff_ = 0;
            }
            rtt_active_ = 0;
            if (!ts_option_)
                rtt_update(now - rtt_ts_);
        }
    }
    if (timerfix_) newtimer(pkt);
    /* update average window */
    awnd_ *= 1.0 - wnd_th_;
    awnd_ += wnd_th_ * cwnd_;
}


/*
 * Respond either to a source quench or to a congestion indication bit.
 * This is done at most once a roundtrip time;  after a source quench,
 * another one will not be done until the last packet transmitted before
 * the previous source quench has been ACKed.
 *
 * Note that this procedure is called before "highest_ack_" is
 * updated to reflect the current ACK packet.  
 */
void TcpAgent::ecn(int seqno)
{
    if (seqno > recover_ || 
          last_cwnd_action_ == CWND_ACTION_TIMEOUT) {
        recover_ =  maxseq_;
        last_cwnd_action_ = CWND_ACTION_ECN;
        if (cwnd_ <= 1.0) {
            if (ecn_backoff_) 
                rtt_backoff();
            else ecn_backoff_ = 1;
        } else ecn_backoff_ = 0;
        slowdown(CLOSE_CWND_HALF|CLOSE_SSTHRESH_HALF);
        ++necnresponses_ ;
        // added by sylvia to count number of ecn responses 
    }
}

/*
 *  Is the connection limited by the network (instead of by a lack
 *    of data from the application?
 */
int TcpAgent::network_limited() {
    int win = window () ;
    if (t_seqno_ > (prev_highest_ack_ + win))
        return 1;
    else
        return 0;
}

void TcpAgent::recv_newack_helper(Packet *pkt) {
    //hdr_tcp *tcph = hdr_tcp::access(pkt);
    newack(pkt);
        if (qs_window_ && highest_ack_ >= qs_window_) {
                // All segments in the QS window have been acknowledged.
                // We can exit the Quick-Start phase.
                qs_window_ = 0;
        }
    if (!ect_ || !hdr_flags::access(pkt)->ecnecho() ||
        (old_ecn_ && ecn_burst_)) {
        /* If "old_ecn", this is not the first ACK carrying ECN-Echo
         * after a period of ACKs without ECN-Echo.
         * Therefore, open the congestion window. */
        /* if control option is set, and the sender is not
             window limited, then do not increase the window size */
        
        if (!control_increase_ || 
           (control_increase_ && (network_limited() == 1))) 
                opencwnd();
    }
    if (ect_) {
        if (!hdr_flags::access(pkt)->ecnecho())
            ecn_backoff_ = 0;
        if (!ecn_burst_ && hdr_flags::access(pkt)->ecnecho())
            ecn_burst_ = TRUE;
        else if (ecn_burst_ && ! hdr_flags::access(pkt)->ecnecho())
            ecn_burst_ = FALSE;
    }
    if (!ect_ && hdr_flags::access(pkt)->ecnecho() &&
        !hdr_flags::access(pkt)->cong_action())
        ect_ = 1;
    /* if the connection is done, call finish() */
    if ((highest_ack_ >= curseq_-1) && !closed_) {
        closed_ = 1;
        finish();
    }
    if (QOption_ && curseq_ == highest_ack_ +1) {
        cancel_rtx_timer();
    }
    if (frto_ == 1) {
        /*
         * New ack after RTO. If F-RTO is enabled, try to transmit new
         * previously unsent segments.
         * If there are no new data or receiver window limits the
         * transmission, revert to traditional recovery.
         */
        if (recover_ + 1 >= highest_ack_ + wnd_ ||
            recover_ + 1 >= curseq_) {
            frto_ = 0;
        } else if (highest_ack_ == recover_) {
            /*
             * F-RTO step 2a) RTO retransmission fixes whole
             * window => cancel F-RTO
             */
            frto_ = 0;
        } else {
            t_seqno_ = recover_ + 1;
            frto_ = 2;
        }
    } else if (frto_ == 2) {
        /*
         * Second new ack after RTO. If F-RTO is enabled, RTO can be
         * declared spurious
         */
        spurious_timeout();
    }
}

/*
 * Set the initial window. 
 */
double
TcpAgent::initial_window()
{
        // If Quick-Start Request was approved, use that as a basis for
        // initial window
        if (qs_cwnd_) {
                return (qs_cwnd_);
        }
    //
    // init_option = 1: static iw of wnd_init_
    //
    if (wnd_init_option_ == 1) {
        return (wnd_init_);
    }
        else if (wnd_init_option_ == 2) {
        // do iw according to Internet draft
        if (size_ <= 1095) {
            return (4.0);
        } else if (size_ < 2190) {
            return (3.0);
        } else {
            return (2.0);
        }
    }
    // XXX what should we return here???
    fprintf(stderr, "Wrong number of wnd_init_option_ %d\n", 
        wnd_init_option_);
    abort();
    return (2.0); // XXX make msvc happy.
}

/*
 * Dupack-action: what to do on a DUP ACK.  After the initial check
 * of 'recover' below, this function implements the following truth
 * table:
 *
 *  bugfix  ecn last-cwnd == ecn    action
 *
 *  0   0   0           tahoe_action
 *  0   0   1           tahoe_action    [impossible]
 *  0   1   0           tahoe_action
 *  0   1   1           slow-start, return
 *  1   0   0           nothing
 *  1   0   1           nothing     [impossible]
 *  1   1   0           nothing
 *  1   1   1           slow-start, return
 */

/* 
 * A first or second duplicate acknowledgement has arrived, and
 * singledup_ is enabled.
 * If the receiver's advertised window permits, and we are exceeding our
 * congestion window by less than numdupacks_, then send a new packet.
 */
void
TcpAgent::send_one()
{
    if (t_seqno_ <= highest_ack_ + wnd_ && t_seqno_ < curseq_ &&
        t_seqno_ <= highest_ack_ + cwnd_ + dupacks_ ) {
        output(t_seqno_, 0);
        if (QOption_)
            process_qoption_after_send () ;
        t_seqno_ ++ ;
        // send_helper(); ??
    }
    return;
}

void
TcpAgent::dupack_action()
{
    int recovered = (highest_ack_ > recover_);
    if (recovered || (!bug_fix_ && !ecn_)) {
        goto tahoe_action;
    }

    if (ecn_ && last_cwnd_action_ == CWND_ACTION_ECN) {
        last_cwnd_action_ = CWND_ACTION_DUPACK;
        slowdown(CLOSE_CWND_ONE);
        reset_rtx_timer(0,0);
        return;
    }

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

tahoe_action:
        recover_ = maxseq_;
        if (!lossQuickStart()) {
        // we are now going to fast-retransmit and willtrace that event
        trace_event("FAST_RETX");
        last_cwnd_action_ = CWND_ACTION_DUPACK;
        slowdown(CLOSE_SSTHRESH_HALF|CLOSE_CWND_ONE);
    }
    reset_rtx_timer(0,0);
    return;
}

/*
 * When exiting QuickStart, reduce the congestion window to the
 *   size that was actually used.
 */
void TcpAgent::endQuickStart()
{
    qs_approved_ = 0;
        qs_cwnd_ = 0;
        qs_window_ = maxseq_;
    int new_cwnd = maxseq_ - last_ack_;
    if (new_cwnd > 1 && new_cwnd < cwnd_) {
        cwnd_ = new_cwnd;
        if (cwnd_ < initial_window()) 
            cwnd_ = initial_window();
    }
}

void TcpAgent::processQuickStart(Packet *pkt)
{
    // QuickStart code from Srikanth Sundarrajan.
    hdr_tcp *tcph = hdr_tcp::access(pkt);
    hdr_qs *qsh = hdr_qs::access(pkt);
    double now = Scheduler::instance().clock();
    int app_rate;

        // printf("flag: %d ttl: %d ttl_diff: %d rate: %d\n", qsh->flag(),
    //     qsh->ttl(), ttl_diff_, qsh->rate());
    qs_requested_ = 0;
    qs_approved_ = 0;
    if (qsh->flag() == QS_RESPONSE && qsh->ttl() == ttl_diff_ && 
            qsh->rate() > 0) {
                app_rate = (int) (hdr_qs::rate_to_Bps(qsh->rate()) *
                      (now - tcph->ts_echo()) / (size_ + headersize()));
#ifdef QS_DEBUG
        printf("Quick Start approved, rate %d, window %d\n", 
                     qsh->rate(), app_rate);
#endif
                if (app_rate > initial_window()) {
            qs_cwnd_ = app_rate;
                        qs_approved_ = 1;
                }
        } else { // Quick Start rejected
#ifdef QS_DEBUG
                printf("Quick Start rejected\n");
#endif
        }

}



/*
 * ACK has been received, hook from recv()
 */
void TcpAgent::recv_frto_helper(Packet *pkt)
{
    hdr_tcp *tcph = hdr_tcp::access(pkt);
    if (tcph->seqno() == last_ack_ && frto_ != 0) {
        /*
         * Duplicate ACK while in F-RTO indicates that the
         * timeout was valid. Go to slow start retransmissions.
         */
        t_seqno_ = highest_ack_ + 1;
        cwnd_ = frto_;
        frto_ = 0;

        // Must zero dupacks (in order to trigger send_much at recv)
        // dupacks is increased in recv after exiting this function
        dupacks_ = -1;
    }
}


/*
 * A spurious timeout has been detected. Do appropriate actions.
 */
void TcpAgent::spurious_timeout()
{
    frto_ = 0;

    switch (spurious_response_) {
    case 1:
    default:
        /*
         * Full revert of congestion window
         * (FlightSize before last acknowledgment)
         */
        cwnd_ = t_seqno_ - prev_highest_ack_;
        break;
 
    case 2:
        /*
         * cwnd = reduced ssthresh (approx. half of the earlier pipe)
         */
        cwnd_ = ssthresh_; break;
    case 3:
        /*
         * slow start, but without retransmissions
         */
        cwnd_ = 1; break;
    }

    /*
     * Revert ssthresh to size before retransmission timeout
     */
    ssthresh_ = pipe_prev_;

    /* If timeout was spurious, bugfix is not needed */
    recover_ = highest_ack_ - 1;
}


/*
 * Loss occurred in Quick-Start window.
 * If Quick-Start is enabled, packet loss in the QS phase should
 * trigger slow start instead of the regular fast retransmit,
 * see [draft-amit-quick-start-03.txt] (to appear).
 * We use variable tcp_qs_recovery_ to toggle this behaviour on and off.
 * If tcp_qs_recovery_ is true, initiate slow start to probe for
 * a correct window size.
 *
 * Return value: non-zero if Quick-Start specific loss recovery took place
 */
int TcpAgent::lossQuickStart()
{
       if (qs_window_ && tcp_qs_recovery_) {
                //recover_ = maxseq_;
                //reset_rtx_timer(1,0);
                slowdown(CLOSE_CWND_INIT);
        // reset ssthresh to half of W-D/2?
                qs_window_ = 0;
                output(last_ack_ + 1, TCP_REASON_DUPACK);
                return 1;
       }
       return 0;
}




/*
 * main reception path - should only see acks, otherwise the
 * network connections are misconfigured
 */
void TcpAgent::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_;
    ts_peer_ = tcph->ts();
    int ecnecho = hdr_flags::access(pkt)->ecnecho();
    if (ecnecho && ecn_)
        ecn(tcph->seqno());
    recv_helper(pkt);
    recv_frto_helper(pkt);
    /* grow cwnd and check if the connection is done */ 
    if (tcph->seqno() > last_ack_) {
        recv_newack_helper(pkt);
        if (last_ack_ == 0 && delay_growth_) { 
            cwnd_ = initial_window();
        }
    } else if (tcph->seqno() == last_ack_) {
                if (hdr_flags::access(pkt)->eln_ && eln_) {
                        tcp_eln(pkt);
                        return;
                }
        if (++dupacks_ == numdupacks_ && !noFastRetrans_) {
            dupack_action();
        } else if (dupacks_ < numdupacks_ && singledup_ ) {
            send_one();
        }
    }

    if (QOption_ && EnblRTTCtr_)
        process_qoption_after_ack (tcph->seqno());

    if (tcph->seqno() >= last_ack_)  
        // Check if ACK is valid.  Suggestion by Mark Allman. 
        valid_ack = 1;
    Packet::free(pkt);
    /*
     * Try to send more data.
     */
    if (valid_ack || aggressive_maxburst_)
        send_much(0, 0, maxburst_);
}

/*
 * Process timeout events other than rtx timeout. Having this as a separate 
 * function allows derived classes to make alterations/enhancements (e.g.,
 * response to new types of timeout events).
 */ 
void TcpAgent::timeout_nonrtx(int tno) 
{
    if (tno == TCP_TIMER_DELSND)  {
     /*
        * delayed-send timer, with random overhead
        * to avoid phase effects
        */
        send_much(1, TCP_REASON_TIMEOUT, maxburst_);
    }
}
    
void TcpAgent::timeout(int tno)
{
    /* retransmit timer */
    if (tno == TCP_TIMER_RTX) {

        // There has been a timeout - will trace this event
        trace_event("TIMEOUT");

        frto_ = 0;
        // Set pipe_prev as per Eifel Response
        pipe_prev_ = (window() > ssthresh_) ?
            window() : (int)ssthresh_;

            if (cwnd_ < 1) cwnd_ = 1;
        if (qs_approved_ == 1) qs_approved_ = 0;
        if (highest_ack_ == maxseq_ && !slow_start_restart_) {
            /*
             * TCP option:
             * If no outstanding data, then don't do anything.  
             */
             // Should this return be here?
             // What if CWND_ACTION_ECN and cwnd < 1?
             // return;
        } else {
            recover_ = maxseq_;
            if (highest_ack_ == -1 && wnd_init_option_ == 2)
                /* 
                 * First packet dropped, so don't use larger
                 * initial windows. 
                 */
                wnd_init_option_ = 1;
            if (highest_ack_ == maxseq_ && restart_bugfix_)
                   /* 
                * if there is no outstanding data, don't cut 
                * down ssthresh_.
                */
                slowdown(CLOSE_CWND_ONE|NO_OUTSTANDING_DATA);
            else if (highest_ack_ < recover_ &&
              last_cwnd_action_ == CWND_ACTION_ECN) {
                   /*
                * if we are in recovery from a recent ECN,
                * don't cut down ssthresh_.
                */
                slowdown(CLOSE_CWND_ONE);
                if (frto_enabled_ || sfrto_enabled_) {
                    frto_ = 1;
                }
            }
            else {
                ++nrexmit_;
                last_cwnd_action_ = CWND_ACTION_TIMEOUT;
                slowdown(CLOSE_SSTHRESH_HALF|CLOSE_CWND_RESTART);
                if (frto_enabled_ || sfrto_enabled_) {
                    frto_ = 1;
                }
            }
        }
        /* if there is no outstanding data, don't back off rtx timer */
        if (highest_ack_ == maxseq_ && restart_bugfix_) {
            reset_rtx_timer(0,0);
        }
        else {
            reset_rtx_timer(0,1);
        }
        last_cwnd_action_ = CWND_ACTION_TIMEOUT;
        send_much(0, TCP_REASON_TIMEOUT, maxburst_);
    } 
    else {
        timeout_nonrtx(tno);
    }
}

/* 
 * Check if the packet (ack) has the ELN bit set, and if it does, and if the
 * last ELN-rxmitted packet is smaller than this one, then retransmit the
 * packet.  Do not adjust the cwnd when this happens.
 */
void TcpAgent::tcp_eln(Packet *pkt)
{
        //int eln_rxmit;
        hdr_tcp *tcph = hdr_tcp::access(pkt);
        int ack = tcph->seqno();

        if (++dupacks_ == eln_rxmit_thresh_ && ack > eln_last_rxmit_) {
                /* Retransmit this packet */
                output(last_ack_ + 1, TCP_REASON_DUPACK);
                eln_last_rxmit_ = last_ack_+1;
        } else
                send_much(0, 0, maxburst_);

        Packet::free(pkt);
        return;
}

/*
 * This function is invoked when the connection is done. It in turn
 * invokes the Tcl finish procedure that was registered with TCP.
 */
void TcpAgent::finish()
{
    Tcl::instance().evalf("%s done", this->name());
}

void RtxTimer::expire(Event*)
{
    a_->timeout(TCP_TIMER_RTX);
}

void DelSndTimer::expire(Event*)
{
    a_->timeout(TCP_TIMER_DELSND);
}

void BurstSndTimer::expire(Event*)
{
    a_->timeout(TCP_TIMER_BURSTSND);
}

/*
 * THE FOLLOWING FUNCTIONS ARE OBSOLETE, but REMAIN HERE
 * DUE TO OTHER PEOPLE's TCPs THAT MIGHT USE THEM
 *
 * These functions are now replaced by ecn() and slowdown(),
 * respectively.
 */

/*
 * Respond either to a source quench or to a congestion indication bit.
 * This is done at most once a roundtrip time;  after a source quench,
 * another one will not be done until the last packet transmitted before
 * the previous source quench has been ACKed.
 */
void TcpAgent::quench(int how)
{
    if (highest_ack_ >= recover_) {
        recover_ =  maxseq_;
        last_cwnd_action_ = CWND_ACTION_ECN;
        closecwnd(how);
    }
}

/*
 * close down the congestion window
 */
void TcpAgent::closecwnd(int how)
{   
    static int first_time = 1;
    if (first_time == 1) {
        fprintf(stderr, "the TcpAgent::closecwnd() function is now deprecated, please use the function slowdown() instead\n");
    }
    switch (how) {
    case 0:
        /* timeouts */
        ssthresh_ = int( window() / 2 );
        if (ssthresh_ < 2)
            ssthresh_ = 2;
        cwnd_ = int(wnd_restart_);
        break;

    case 1:
        /* Reno dup acks, or after a recent congestion indication. */
        // cwnd_ = window()/2;
        cwnd_ = decrease_num_ * window();
        ssthresh_ = int(cwnd_);
        if (ssthresh_ < 2)
            ssthresh_ = 2;      
        break;

    case 2:
        /* Tahoe dup acks       
         * after a recent congestion indication */
        cwnd_ = wnd_init_;
        break;

    case 3:
        /* Retransmit timeout, but no outstanding data. */ 
        cwnd_ = int(wnd_init_);
        break;
    case 4:
        /* Tahoe dup acks */
        ssthresh_ = int( window() / 2 );
        if (ssthresh_ < 2)
            ssthresh_ = 2;
        cwnd_ = 1;
        break;

    default:
        abort();
    }
    fcnt_ = 0.;
    count_ = 0;
}

/*
 * Check if the sender has been idle or application-limited for more
 * than an RTO, and if so, reduce the congestion window.
 */
void TcpAgent::process_qoption_after_send ()
{
    int tcp_now = (int)(Scheduler::instance().clock()/tcp_tick_ + 0.5);
    int rto = (int)(t_rtxcur_/tcp_tick_) ; 
    /*double ct = Scheduler::instance().clock();*/

    if (!EnblRTTCtr_) {
        if (tcp_now - T_last >= rto) {
            // The sender has been idle.
            slowdown(THREE_QUARTER_SSTHRESH|TCP_IDLE) ;
            for (int i = 0 ; i < (tcp_now - T_last)/rto; i ++) {
                slowdown(CWND_HALF_WITH_MIN|TCP_IDLE);
            }
            T_prev = tcp_now ;
            W_used = 0 ;
        }
        T_last = tcp_now ;
        if (t_seqno_ == highest_ack_+ window()) {
            T_prev = tcp_now ; 
            W_used = 0 ; 
        }
        else if (t_seqno_ == curseq_-1) {
            // The sender has no more data to send.
            int tmp = t_seqno_ - highest_ack_ ;
            if (tmp > W_used)
                W_used = tmp ;
            if (tcp_now - T_prev >= rto) {
                // The sender has been application-limited.
                slowdown(THREE_QUARTER_SSTHRESH|TCP_IDLE);
                slowdown(CLOSE_CWND_HALF_WAY|TCP_IDLE);
                T_prev = tcp_now ;
                W_used = 0 ;
            }
        }
    } else {
        rtt_counting();
    }
}

/*
 * Check if the sender has been idle or application-limited for more
 * than an RTO, and if so, reduce the congestion window, for a TCP sender
 * that "counts RTTs" by estimating the number of RTTs that fit into
 * a single clock tick.
 */
void
TcpAgent::rtt_counting()
{
        int tcp_now = (int)(Scheduler::instance().clock()/tcp_tick_ + 0.5);
    int rtt = (int(t_srtt_) >> T_SRTT_BITS) ;

    if (rtt < 1) 
        rtt = 1 ;
    if (tcp_now - T_last >= 2*rtt) {
        // The sender has been idle.
        int RTTs ; 
        RTTs = (tcp_now -T_last)*RTT_goodcount/(rtt*2) ; 
        RTTs = RTTs - Backoffs ; 
        Backoffs = 0 ; 
        if (RTTs > 0) {
            slowdown(THREE_QUARTER_SSTHRESH|TCP_IDLE) ;
            for (int i = 0 ; i < RTTs ; i ++) {
                slowdown(CWND_HALF_WITH_MIN|TCP_IDLE);
                RTT_prev = RTT_count ; 
                W_used = 0 ;
            }
        }
    }
    T_last = tcp_now ;
    if (tcp_now - T_start >= 2*rtt) {
        if ((RTT_count > RTT_goodcount) || (F_full == 1)) {
            RTT_goodcount = RTT_count ; 
            if (RTT_goodcount < 1) RTT_goodcount = 1 ; 
        }
        RTT_prev = RTT_prev - RTT_count ;
        RTT_count = 0 ; 
        T_start  = tcp_now ;
        F_full = 0;
    }
    if (t_seqno_ == highest_ack_ + window()) {
        W_used = 0 ; 
        F_full = 1 ; 
        RTT_prev = RTT_count ;
    }
    else if (t_seqno_ == curseq_-1) {
        // The sender has no more data to send.
        int tmp = t_seqno_ - highest_ack_ ;
        if (tmp > W_used)
            W_used = tmp ;
        if (RTT_count - RTT_prev >= 2) {
            // The sender has been application-limited.
            slowdown(THREE_QUARTER_SSTHRESH|TCP_IDLE) ;
            slowdown(CLOSE_CWND_HALF_WAY|TCP_IDLE);
            RTT_prev = RTT_count ; 
            Backoffs ++ ; 
            W_used = 0;
        }
    }
    if (F_counting == 0) {
        W_timed = t_seqno_  ;
        F_counting = 1 ;
    }
}

void TcpAgent::process_qoption_after_ack (int seqno)
{
    if (F_counting == 1) {
        if (seqno >= W_timed) {
            RTT_count ++ ; 
            F_counting = 0 ; 
        }
        else {
            if (dupacks_ == numdupacks_)
                RTT_count ++ ;
        }
    }
}

void TcpAgent::trace_event(char *eventtype)
{
    if (et_ == NULL) return;
    int seqno = t_seqno_;
    char *wrk = et_->buffer();
    char *nwrk = et_->nbuffer();
    if (wrk != 0)
        sprintf(wrk,
            "E "TIME_FORMAT" %d %d TCP %s %d %d %d",
            et_->round(Scheduler::instance().clock()),   // time
            addr(),                       // owner (src) node id
            daddr(),                      // dst node id
            eventtype,                    // event type
            fid_,                         // flow-id
            seqno,                        // current seqno
            int(cwnd_)                         //cong. window
            );
    
    if (nwrk != 0)
        sprintf(nwrk,
            "E -t "TIME_FORMAT" -o TCP -e %s -s %d.%d -d %d.%d",
            et_->round(Scheduler::instance().clock()),   // time
            eventtype,                    // event type
            addr(),                       // owner (src) node id
            port(),                       // owner (src) port id
            daddr(),                      // dst node id
            dport()                       // dst port id
            );
    et_->trace();
}

---