1 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */ 2 /* 3 * Copyright (c) 2007 Emmanuelle Laprise 4 * 5 * This program is free software; you can redistribute it and/or modify 6 * it under the terms of the GNU General Public License version 2 as 7 * published by the Free Software Foundation; 8 * 9 * This program is distributed in the hope that it will be useful, 10 * but WITHOUT ANY WARRANTY; without even the implied warranty of 11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 * GNU General Public License for more details. 13 * 14 * You should have received a copy of the GNU General Public License 15 * along with this program; if not, write to the Free Software 16 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA 17 * 18 * Author: Emmanuelle Laprise <emmanuelle.laprise@bluekazoo.ca 19 * Derived from the p2p net device file 20 Transmi */ 21 22 #ifndef BACKOFF_H 23 #define BACKOFF_H 24 25 #include <stdint.h> 26 #include "ns3/nstime.h" 27 #include "ns3/random-variable-stream.h" 28 29 namespace ns3 { 30 31 /** 32 * \ingroup csma 33 * \brief The backoff class is used for calculating backoff times 34 * when many net devices can write to the same channel 35 */ 36 37 class Backoff { 38 public: 39 /** 40 * Minimum number of backoff slots (when multiplied by m_slotTime, determines minimum backoff time) 41 */ 42 uint32_t m_minSlots; 43 44 /** 45 * Maximum number of backoff slots (when multiplied by m_slotTime, determines maximum backoff time) 46 */ 47 uint32_t m_maxSlots; 48 49 /** 50 * Caps the exponential function when the number of retries reaches m_ceiling. 51 */ 52 uint32_t m_ceiling; 53 54 /** 55 * Maximum number of transmission retries before the packet is dropped. 56 */ 57 uint32_t m_maxRetries; 58 59 /** 60 * Length of one slot. A slot time, it usually the packet transmission time, if the packet size is fixed. 61 */ 62 Time m_slotTime; 63 64 Backoff (void); 65 /** 66 * \brief Constructor 67 * \param slotTime Length of one slot 68 * \param minSlots Minimum number of backoff slots 69 * \param maxSlots Maximum number of backoff slots 70 * \param ceiling Cap to the exponential function 71 * \param maxRetries Maximum number of transmission retries 72 */ 73 Backoff (Time slotTime, uint32_t minSlots, uint32_t maxSlots, uint32_t ceiling, uint32_t maxRetries); 74 75 /** 76 * \return The amount of time that the net device should wait before 77 * trying to retransmit the packet 78 */ 79 Time GetBackoffTime (); 80 81 /** 82 * Indicates to the backoff object that the last packet was 83 * successfully transmitted and that the number of retries should be 84 * reset to 0. 85 */ 86 void ResetBackoffTime (void); 87 88 /** 89 * \return True if the maximum number of retries has been reached 90 */ 91 bool MaxRetriesReached (void); 92 93 /** 94 * Increments the number of retries by 1. 95 */ 96 void IncrNumRetries (void); 97 98 /** 99 * Assign a fixed random variable stream number to the random variables 100 * used by this model. Return the number of streams (possibly zero) that 101 * have been assigned. 102 * 103 * \param stream first stream index to use 104 * \return the number of stream indices assigned by this model 105 */ 106 int64_t AssignStreams (int64_t stream); 107 108 private: 109 110 /** 111 * Number of times that the transmitter has tried to unsuccessfully transmit the current packet. 112 */ 113 uint32_t m_numBackoffRetries; 114 115 /** 116 * Random number generator 117 */ 118 Ptr<UniformRandomVariable> m_rng; 119 }; 120 121 } // namespace ns3 122 123 #endif /* BACKOFF_H */ 124