tcp.cc

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/* -*-  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;
#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;
        /* 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;
}

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;

        //
        // srtt has 3 bits to the right of the binary point
        // rttvar has 2
        //
        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();
        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_) {
                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);
                        if (rate_request_ > 0) {
                                // QuickStart code from Srikanth Sundarrajan.
                                qsh->flag() = QS_REQUEST;
                                Random::seed_heuristically();
                                qsh->ttl() = Random::integer(256);
                                ttl_diff_ = (iph->ttl() - qsh->ttl()) % 256;
                                qsh->rate() = rate_request_;
                                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));
}

int TcpAgent::window()
{
        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) {
                        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;
                                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 packet drop rate p for highspeed TCP.
 */
double TcpAgent::compute_p()
{
        double p;
        double low_p = 1.5/(low_window_*low_window_);
        p = exp(linear(log(cwnd_), log(low_window_), log(low_p), log(high_window_), log(high_p_)));
        return p;
}

/*
 * Calculating the decrease parameter for highspeed TCP.
 */
double TcpAgent::decrease_param()
{
        double decrease;
        decrease = linear(log(cwnd_), log(low_window_), 0.5, log(high_window_), high_decrease_);
        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_ >= cwnd_last_ && cwnd_ < cwnd_frac_ * cwnd_last_ ) {
                answer = increase_last_ / cwnd_;
                return answer;
       } else { 
                p = compute_p();
                decrease = decrease_param();
                increase = (cwnd_ * cwnd_ *2.0* decrease * p)/(2.0 - decrease); 
                //      double max_increase = 157.8;
                //      if (increase > max_increase) { 
                //              increase = max_increase;
                //      } 
                answer = increase / cwnd_;
                cwnd_last_ = cwnd_;
                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. */
                        f = (t_srtt_ >> T_SRTT_BITS) * tcp_tick_;
                        f *= f;
                        f *= wnd_const_;
                        f += fcnt_;
                        if (f > cwnd_) {
                                fcnt_ = 0;
                                ++cwnd_;
                        } else
                                fcnt_ = f;
                        break;

                case 3:
                        f = awnd_;
                        f *= f;
                        f *= wnd_const_;
                        f += fcnt_;
                        if (f > cwnd_) {
                                fcnt_ = 0;
                                ++cwnd_;
                        } else
                                fcnt_ = f;
                        break;

                case 4:
                        f = awnd_;
                        f *= wnd_const_;
                        f += fcnt_;
                        if (f > cwnd_) {
                                fcnt_ = 0;
                                ++cwnd_;
                        } else
                                fcnt_ = f;
                        break;
                case 5:
                        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 */
                        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_; 
        // 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_)
                        rtt_update(now - tcph->ts_echo());

                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 (!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();
        }
}

/*
 * Set the initial window. 
 */
double
TcpAgent::initial_window()
{
        //
        // 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:
        // we are now going to fast-retransmit and willtrace that event
        trace_event("FAST_RETX");

        recover_ = maxseq_;
        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;
        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) (qsh->rate() * (now - tcph->ts_echo())) ;
                printf("Quick Start approved, rate %d, window %d\n", 
                                     qsh->rate(), app_rate);
                if (app_rate > initial_window()) {
                        wnd_init_option_ = 1;
                        wnd_init_ = app_rate;
                        qs_approved_ = 1;
                }
        } else { // Quick Start rejected
                printf("Quick Start rejected\n");
        }

}

/*
 * 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);
        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);
        /* 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());

        Packet::free(pkt);
        /*
         * Try to send more data.
         */
        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");

                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);
                        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);
                        }
                        else {
                                ++nrexmit_;
                                last_cwnd_action_ = CWND_ACTION_TIMEOUT;
                                slowdown(CLOSE_SSTHRESH_HALF|CLOSE_CWND_RESTART);
                        }
                }
                /* 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) ;
                        for (int i = 0 ; i < (tcp_now - T_last)/rto; i ++) {
                                slowdown(CWND_HALF_WITH_MIN);
                        }
                        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);
                                slowdown(CLOSE_CWND_HALF_WAY);
                                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) ;
                        for (int i = 0 ; i < RTTs ; i ++) {
                                slowdown(CWND_HALF_WITH_MIN);
                                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) ;
                        slowdown(CLOSE_CWND_HALF_WAY);
                        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();
}

---