tcp-asym.cc

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/*
 * tcp-asym includes modifications to several flavors of TCP to enhance
 * performance over asymmetric networks, where the ack channel is
 * constrained.  Types of asymmetry we have studied and used these mods
 * include bandwidth asymmetry and latency asymmetry (where  variable 
 * latencies cause problems to TCP, e.g., in packet radio networks.
 * The sender-side modifications in this file are structured as helper 
 * functions that are invoked from various points in the TCP code. The main
 * additional functionality is (a) the sender increases its congestion window
 * in proportion to the amount of data acked rather than the number of acks
 * received, (b) it breaks up potentially large bursts into smaller ones 
 * when acks are few and far between by rate-based pacing, and 
 * (c) it copies the ecn_to_echo_ bit from acks into subsequent data packets, 
 * using which the sink can perform ack congestion control (tcp-asym-sink.cc). 
 * The tcp-asym source is usually used in conjunction with a tcp-asym sink, or
 * with a router/end-host implementing ack filtering (semantic-packetqueue.cc).
 * 
 * For questions/comments, please contact:
 *   Venkata N. Padmanabhan (padmanab@cs.berkeley.edu)
 *   http://www.cs.berkeley.edu/~padmanab
 */ 

#ifndef lint
static const char rcsid[] =
    "@(#) $Header: /nfs/jade/vint/CVSROOT/ns-2/tcp/tcp-asym.cc,v 1.17 1999/09/09 03:22:50 salehi Exp $ (UCB)";
#endif

#include "tcp-asym.h"

int hdr_tcpasym::offset_;

static class TCPAHeaderClass : public PacketHeaderClass {
public:
        TCPAHeaderClass() : PacketHeaderClass("PacketHeader/TCPA",
                                             sizeof(hdr_tcpasym)) {
                bind_offset(&hdr_tcpasym::offset_);
        }
} class_tcpahdr;

static class TcpAsymClass : public TclClass {
public:
        TcpAsymClass() : TclClass("Agent/TCP/Asym") {}
        TclObject* create(int, const char*const*) {
                return (new TcpAsymAgent());
        } 
} class_tcpasym;


TcpAsymAgent::TcpAsymAgent() : TcpAgent(), ecn_to_echo_(0), t_exact_srtt_(0)
{
/*      bind("exact_srtt_", &t_exact_srtt_);*/
        bind("g_", &g_);
/*      bind("avg_win_", &avg_win_);*/
/*      bind("damp_", &damp_);*/
}


static class TcpRenoAsymClass : public TclClass {
public:
        TcpRenoAsymClass() : TclClass("Agent/TCP/Reno/Asym") {}
        TclObject* create(int, const char*const*) {
                return (new TcpRenoAsymAgent());
        } 
} class_tcprenoasym;


static class NewRenoTcpAsymClass : public TclClass {
public:
        NewRenoTcpAsymClass() : TclClass("Agent/TCP/Newreno/Asym") {}
        TclObject* create(int, const char*const*) {
                return (new NewRenoTcpAsymAgent());
        } 
} class_newrenotcpasym;


/* The helper functions */

/* fill in the TCP asym header before packet is sent out */
void TcpAsymAgent::output_helper(Packet* p) 
{
        hdr_tcpasym *tcpha = hdr_tcpasym::access(p);
        hdr_flags *flagsh = hdr_flags::access(p);

        tcpha->win() = min(highest_ack_+window(), curseq_) - t_seqno_;
        tcpha->highest_ack() = highest_ack_;
        tcpha->max_left_to_send() = curseq_ - highest_ack_; /* XXXX not needed? */

        flagsh->ecnecho() = ecn_to_echo_;
        ecn_to_echo_ = 0;
}

/* schedule the next burst of data (of size at most maxburst) */
void TcpAsymAgent::send_helper(int maxburst) 
{
        /* 
         * If there is still data to be sent and there is space in the
         * window, set a timer to schedule the next burst. Note that
         * we wouldn't get here if TCP_TIMER_BURSTSEND were pending,
         * so we do not need an explicit check here.
         */
        if (t_seqno_ <= highest_ack_ + window() && t_seqno_ < curseq_) {
                burstsnd_timer_.resched(t_exact_srtt_*maxburst/window());
        }
}

/* check if the received ack has an ECN that needs to be echoed back to the sink */
void TcpAsymAgent::recv_helper(Packet *pkt) 
{
        if (hdr_flags::access(pkt)->ce())
                ecn_to_echo_ = 1;
}

/* open cwnd in proportion to the amount of data acked */
void TcpAsymAgent::recv_newack_helper(Packet *pkt) 
{
        int i;
        hdr_tcp *tcph = hdr_tcp::access(pkt);
        int ackcount = tcph->seqno() - last_ack_;
        double tao = Scheduler::instance().clock() - tcph->ts_echo();

        newack(pkt);
        /* update our fine-grained estimate of the smoothed RTT */
        if (t_exact_srtt_ != 0) 
                t_exact_srtt_ = g_*tao + (1-g_)*t_exact_srtt_;
        else
                t_exact_srtt_ = tao;
/*      avg_win_ = g_*window() + (1-g_)*avg_win_;*/
        /* grow cwnd */
        for (i=0; i<ackcount; i++)
                opencwnd();
        /* if the connection is done, call finish() */
        if ((highest_ack_ >= curseq_-1) && !closed_) {
                closed_ = 1;
                finish();
        }
}       


/* Print out if tcp-asym-specific variables have been modified */
void TcpAsymAgent::traceVar(TracedVar* v) {
        Scheduler& s = Scheduler::instance();
        char wrk[500];

        double curtime = &s ? s.clock() : 0;
        if (!strcmp(v->name(), "exact_srtt_"))
                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(), "avg_win_"))
                sprintf(wrk,"%-8.5f %-2d %-2d %-2d %-2d %s %-6.3f", 
                        curtime, addr(), port(), daddr(), dport(), 
                        v->name(), double(*((TracedDouble*) v)));
        else {
                TcpAgent::traceVar(v);
                return;
        }

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

        TcpAgent::traceAll();
        curtime = &s ? s.clock() : 0;
        sprintf(wrk, "time: %-8.5f saddr: %-2d sport: %-2d daddr: %-2d dport:"
                " %-2d exact_srtt %d", curtime, addr(), port(),
                daddr(), dport(), (int(t_exact_srtt_)));
        n = strlen(wrk);
        wrk[n] = '\n';
        wrk[n+1] = 0;
        if (channel_)
                (void)Tcl_Write(channel_, wrk, n+1);
        wrk[n] = 0;
        return;
}

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