mac-csma.cc

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/* -*-  Mode:C++; c-basic-offset:8; tab-width:8; indent-tabs-mode:t -*- */
/*
 * Copyright (c) 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 Daedalus Research
 *  Group at the University of California Berkeley.
 * 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
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 * 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.
 *
 * Contributed by Giao Nguyen, http://daedalus.cs.berkeley.edu/~gnguyen
 */

#ifndef lint
static const char rcsid[] =
    "@(#) $Header: /nfs/jade/vint/CVSROOT/ns-2/mac/mac-csma.cc,v 1.26 1998/11/17 23:36:35 yuriy Exp $ (UCB)";
#endif

#include "template.h"
#include "random.h"
#include "channel.h"
#include "mac-csma.h"

static class MacCsmaClass : public TclClass {
public:
    MacCsmaClass() : TclClass("Mac/Csma") {}
    TclObject* create(int, const char*const*) {
        return (new MacCsma);
    }
} class_mac_csma;

static class MacCsmaCdClass : public TclClass {
public:
    MacCsmaCdClass() : TclClass("Mac/Csma/Cd") {}
    TclObject* create(int, const char*const*) {
        return (new MacCsmaCd);
    }
} class_mac_csma_cd;

static class MacCsmaCaClass : public TclClass {
public:
    MacCsmaCaClass() : TclClass("Mac/Csma/Ca") {}
    TclObject* create(int, const char*const*) {
        return (new MacCsmaCa);
    }
} class_mac_csma_ca;


void
MacHandlerEoc::handle(Event* e)
{
    mac_->endofContention((Packet*)e);
}


MacCsma::MacCsma() : txstart_(0), rtx_(0), csense_(1), hEoc_(this)
{
    bind_time("ifs_", &ifs_);
    bind_time("slotTime_", &slotTime_);
    bind("cwmin_", &cwmin_);
    bind("cwmax_", &cwmax_);
    bind("rtxLimit_", &rtxLimit_);
    bind("csense_", &csense_);
    cw_ = cwmin_;
}


void MacCsma::resume(Packet* p)
{
    Scheduler& s = Scheduler::instance();
    s.schedule(callback_, &intr_, ifs_ + slotTime_ * cwmin_);
    if (p != 0)
        drop(p);
    callback_ = 0;
    state(MAC_IDLE);
    rtx_ = 0;
    cw_ = cwmin_;
}


void MacCsma::send(Packet* p)
{
    Scheduler& s = Scheduler::instance();
    double delay = channel_->txstop() + ifs_ - s.clock();

    // if channel is not ready, then wait
    // else content for the channel

    /* XXX floating point operations differences have been
       observed on the resulting delay value on Pentium II and
       SunSparc.  E.g.
                               PentiumII                   SunSparc
                               -------------------------------
       channel_->txstop_=      0.11665366666666668         0.11665366666666668
                       binary    0x3fbddd03c34ab4a2          0x3fbddd03c34ab4a2
       ifs_=                   5.1999999999999997e-05      5.1999999999999997e-05
                       binary    0x3f0b43526527a205          0x3f0b43526527a205
       s.clock_=               0.11670566666666668         0.11670566666666668
                       binary    0x3fbde06c2d975996          0x3fbde06c2d975996

       delay=                  3.5033282698437862e-18      0
                       binary    0x3c50280000000000          0x0000000000000000

       Because of that the value of (csense_ && delay > 0) was different.  Fixed by
       changing 0 to EPS
     */
    static const double EPS= 1.0e-12; //seems appropriate (less than nanosec)
    if (csense_ && delay > EPS)
        s.schedule(&hSend_, p, delay + 0.000001);
    else {
        txstart_ = s.clock();
        channel_->contention(p, &hEoc_);
    }
}


void MacCsma::backoff(Handler* h, Packet* p, double delay)
{
    Scheduler& s = Scheduler::instance();
    double now = s.clock();

    // if retransmission time within limit, do exponential backoff
    // else drop the packet and resume
    if (++rtx_ < rtxLimit_) {
        delay += max(channel_->txstop() + ifs_ - now, 0.0);
        int slot = Random::integer(cw_);
        s.schedule(h, p, delay + slotTime_ * slot);
        cw_ = min(2 * cw_, cwmax_);
    }
    else
        resume(p);
}


void MacCsma::endofContention(Packet* p)
{
    Scheduler& s = Scheduler::instance();
    double txt = txtime(p) - (s.clock() - txstart_);
    hdr_mac::access(p)->txtime() = txt;
    channel_->send(p, txt);
    s.schedule(&hRes_, &eEoc_, txt);
    rtx_ = 0;
    cw_ = cwmin_;
}


void MacCsmaCd::endofContention(Packet* p)
{
    // If there is a collision, backoff
    if (channel_->collision()) {
        channel_->jam(0);
        backoff(&hSend_, p);
    }
    else
        MacCsma::endofContention(p);
}


void MacCsmaCa::send(Packet* p)
{
    Scheduler& s = Scheduler::instance();
    double delay = channel_->txstop() + ifs_ - s.clock();

    if (csense_ && delay > 0)
        backoff(&hSend_, p);
    else {
        txstart_ = s.clock();
        channel_->contention(p, &hEoc_);
    }
}

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