backoff.h

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/*
 * Copyright (c) 2007 Emmanuelle Laprise
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation;
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * Author: Emmanuelle Laprise <emmanuelle.laprise@bluekazoo.ca
 * Derived from the p2p net device file
Transmi */
 
#ifndef BACKOFF_H
#define BACKOFF_H
 
#include "ns3/nstime.h"
#include "ns3/random-variable-stream.h"
 
#include <stdint.h>
 
namespace ns3
{
 
/**
 * \ingroup csma
 * \brief The backoff class is used for calculating backoff times
 * when many net devices can write to the same channel
 */
 
class Backoff
{
  public:
    /**
     * Minimum number of backoff slots (when multiplied by m_slotTime, determines minimum backoff
     * time)
     */
    uint32_t m_minSlots;
 
    /**
     * Maximum number of backoff slots (when multiplied by m_slotTime, determines maximum backoff
     * time)
     */
    uint32_t m_maxSlots;
 
    /**
     * Caps the exponential function when the number of retries reaches m_ceiling.
     */
    uint32_t m_ceiling;
 
    /**
     * Maximum number of transmission retries before the packet is dropped.
     */
    uint32_t m_maxRetries;
 
    /**
     * Length of one slot. A slot time, it usually the packet transmission time, if the packet size
     * is fixed.
     */
    Time m_slotTime;
 
    Backoff();
    /**
     * \brief Constructor
     * \param slotTime Length of one slot
     * \param minSlots Minimum number of backoff slots
     * \param maxSlots Maximum number of backoff slots
     * \param ceiling Cap to the exponential function
     * \param maxRetries Maximum number of transmission retries
     */
    Backoff(Time slotTime,
            uint32_t minSlots,
            uint32_t maxSlots,
            uint32_t ceiling,
            uint32_t maxRetries);
 
    /**
     * \return The amount of time that the net device should wait before
     * trying to retransmit the packet
     */
    Time GetBackoffTime();
 
    /**
     * Indicates to the backoff object that the last packet was
     * successfully transmitted and that the number of retries should be
     * reset to 0.
     */
    void ResetBackoffTime();
 
    /**
     * \return True if the maximum number of retries has been reached
     */
    bool MaxRetriesReached() const;
 
    /**
     * Increments the number of retries by 1.
     */
    void IncrNumRetries();
 
    /**
     * Assign a fixed random variable stream number to the random variables
     * used by this model.  Return the number of streams (possibly zero) that
     * have been assigned.
     *
     * \param stream first stream index to use
     * \return the number of stream indices assigned by this model
     */
    int64_t AssignStreams(int64_t stream);
 
  private:
    /**
     * Number of times that the transmitter has tried to unsuccessfuly transmit the current packet.
     */
    uint32_t m_numBackoffRetries;
 
    /**
     * Random number generator
     */
    Ptr<UniformRandomVariable> m_rng;
};
 
} // namespace ns3
 
#endif /* BACKOFF_H */