ack-recons.cc

Go to the documentation of this file.

/* -*-  Mode:C++; c-basic-offset:8; tab-width:8; indent-tabs-mode:t -*- */
/*
 * Copyright (c) 1997 The 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 Daedalus Research
 *  Group at the University of California at Berkeley.
 * 4. Neither the name of the University nor of the Research Group 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.
 *
 * ack-recons.cc: contributed by the Daedalus Research Group, 
 * UC Berkeley (http://daedalus.cs.berkeley.edu).
 *
 * $Header: /nfs/jade/vint/CVSROOT/ns-2/tcp/ack-recons.cc,v 1.6 2000/09/01 03:04:05 haoboy Exp $
 */

/*
 * TCP Ack reconstructor.  This object sits on the other end of a constrained 
 * link and intersperses TCP acks to the source (without violating the e2e 
 * semantics of TCP acks).  This allows us to get good performance for TCP 
 * over various asymmetric networks, in conjunction with techniques to reduce 
 * the frequency of acks (such as ack filtering) with making any changes to 
 * the TCP source (e.g., like those implemented in tcp-asym.cc).  
 */

#include "template.h"
#include "ack-recons.h"

static class AckReconsControllerClass : public TclClass {
public:
    AckReconsControllerClass() : TclClass("AckReconsControllerClass") { }
    TclObject* create(int, const char*const*) {
        return (new AckReconsController);
    }
} class_ackrecons_controller;

static class AckReconsClass : public TclClass {
public:
    AckReconsClass() : TclClass("Agent/AckReconsClass") { }
    TclObject* create(int, const char*const* argv) {
        return new AckRecons(atoi(argv[4]), atoi(argv[5]));
    }
} class_ackrecons;

/*
 * Demux a packet to the right ack reconstructor.
 */
void
AckReconsController::recv(Packet *p, Handler *)
{
    Tcl& tcl = Tcl::instance();
    hdr_ip *ip = hdr_ip::access(p);
    tcl.evalf("%s demux %d %d", name(),
          ip->saddr(), ip->daddr());
    AckRecons *ackRecons = 
        (AckRecons *) TclObject::lookup(tcl.result());
    if (ackRecons == NULL) {
        printf("Error: malformed ack reconstructor\n");
        abort();
    }
    ackRecons->spq_ = spq_;
    ackRecons->recv(p);
}

void 
AckRecons::recv(Packet *pkt)
{
    double now = Scheduler::instance().clock();
    hdr_tcp *tcph = hdr_tcp::access(pkt);
    int &ack = tcph->seqno(), a, i;
    Tcl& tcl = Tcl::instance();
#ifdef DEBUG
    printf("%f\tRecd ack %d\n", now, ack);
#endif
    if (ackTemplate_ == 0)
        ackTemplate_ = pkt->copy();
    if (adaptive_)
        tcl.evalf("%s ackbw %d %f\n", name(), ack, now);
    /* The ack spacing policy is implemented in Tcl for flexibility */
    tcl.evalf("%s spacing %d\n", name(), ack);
    /* 
     * If the difference in acks is less than a threshold, let
     * it go through.  Later, we will look for rapid ack arrivals
     * to smooth them out and avoid the adverse effects of ack comp.
     */
    if ((!ackPending_ && ack-lastAck_ <= deltaAckThresh_) || dupacks_) {
        if (ack == lastRealAck_)
            dupacks_++;
        else if (ack > lastAck_) {
            dupacks_ = 0;
            lastAck_ = ack;
            lastTime_ = now;
        }
        spq_->reconsAcks_ = 0;
        spq_->enque(pkt);
        spq_->reconsAcks_ = 1;
#ifdef DEBUG
        printf("\t%f\tEnqueuing ack %d in order\n", now, ack);
#endif
    } else {
        if (ack == lastRealAck_)
            dupacks_++;
        /* Intersperse some acks and schedule their transmissions. */
        double starttime = max(now, lastTime_);
        for (a = lastAck_+delack_, i=0; a <= ack; a += delack_, i++)
            sendack(a, starttime + i*ackSpacing_ - now);
        if ((a-ack)%delack_)
            sendack(ack, starttime + i*ackSpacing_ - now);
        Packet::free(pkt);
    }
    if (ack >= lastRealAck_) {
        lastRealAck_ = ack;
        lastRealTime_ = now;
    }
}

int
AckRecons::command(int argc, const char*const* argv)
{
    return Agent::command(argc, argv);
}

/*
 * Arrange to send ack a at time t from now.
 */
void
AckRecons::sendack(int ack, double t)
{
    Packet *ackp = ackTemplate_->copy();
    Scheduler &s = Scheduler::instance();
    hdr_tcp *th = hdr_tcp::access(ackp);
    th->seqno() = ack;
    /* Set no_ts_ in flags because we don't want an rtt sample for this */
    if (th->ts() == hdr_tcp::access(ackp)->ts()) {
        hdr_flags *fh = hdr_flags::access(ackp);
        fh->no_ts_ = 1;
        th->ts_ = s.clock();    /* for debugging purposes only */
    }
    s.schedule((Handler *)this, (Event *)ackp, t);
    ackPending_++;
#ifdef DEBUG
    printf("\t%f\tScheduling ack %d to be sent at %f\n", 
           s.clock(), ack, s.clock() + t);
#endif
}

/* 
 * Handle scheduling of acks.
 */
void
AckRecons::handle(Event *e)
{
    Packet *p = (Packet *) e;
    hdr_tcp *th = hdr_tcp::access(p);
    ackPending_--;
    if (lastAck_ < th->seqno()) {
        spq_->reconsAcks_ = 0;
        /* 
         * need to do queue's recv here, so that a deque is
         * forced if the queue isn't blocked.  It's not
         * sufficient to call spq_->recv() alone.
         */
        target_->recv(p); /* maybe do acksfirst for this ack? */
        spq_->reconsAcks_ = 1;
        lastTime_ = Scheduler::instance().clock();
        lastAck_ = th->seqno();
#ifdef DEBUG
        printf("%f\tSending scheduled ack %d\n",lastTime_,th->seqno());
#endif
    } else {
        Packet::free(p);
#ifdef DEBUG
        printf("%f\tack %d superceded by ack %d at %f\n", 
               Scheduler::instance().clock(), th->seqno(), lastAck_,
               lastTime_);
#endif
    }
}

---