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Sending Multicast Packet Over 802.11 Network in NS-2 Simulation

Learn how to send multicast packets over 802.11 network in NS-2 simulation platform by tracing mac-802_11.cc and mac-802_11.h files under mac folder. Study the procedure for receiving, sending, sending DATA, sending RTS, starting defer timer, defer handler, checking packet transmission, and more. Understand the code snippets and functions involved in transmitting and handling packets.

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Sending Multicast Packet Over 802.11 Network in NS-2 Simulation

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  1. How to send a multicast packet over 802.11 network? Trace mac-802_11.cc and mac-802_11.h under mac folder of ns-2.28

  2. Procedure recv() -> send() -> sendDATA() and sendRTS() -> start defer timer -> deferHandler() -> check_pktTx() -> transmit() -> done!

  3. recv() void Mac802_11::recv(Packet *p, Handler *h) { struct hdr_cmn *hdr = HDR_CMN(p); assert(initialized()); if( hdr->direction() == hdr_cmn::DOWN ) { send(p, h); return; } ………………………………….. } Back to procedure

  4. send( ) void Mac802_11::send(Packet *p, Handler *h) { double rTime; struct hdr_mac802_11* dh = HDR_MAC802_11(p); EnergyModel *em = netif_->node()->energy_model(); if (em && em->sleep()) { em->set_node_sleep(0); em->set_node_state(EnergyModel::INROUTE); } callback_ = h; sendDATA(p); sendRTS(ETHER_ADDR(dh->dh_ra)); dh->dh_scontrol = sta_seqno_++; if(mhBackoff_.busy() == 0) { if(is_idle()) { if (mhDefer_.busy() == 0) { rTime = (Random::random() % cw_) * (phymib_.getSlotTime()); mhDefer_.start(phymib_.getDIFS() + rTime); } } else { mhBackoff_.start(cw_, is_idle()); } } } Back to procedure

  5. if((u_int32_t)ETHER_ADDR(dh->dh_ra) != MAC_BROADCAST) { /* store data tx time for unicast packets */ ch->txtime() = txtime(ch->size(), dataRate_); dh->dh_duration = usec(txtime(phymib_.getACKlen(), basicRate_) + phymib_.getSIFS()); } else { /* store data tx time for broadcast packets (see 9.6) */ ch->txtime() = txtime(ch->size(), basicRate_ ); dh->dh_duration = 0; } pktTx_ = p; } Mac802_11::sendDATA(Packet *p) { hdr_cmn* ch = HDR_CMN(p); struct hdr_mac802_11* dh = HDR_MAC802_11(p); assert(pktTx_ == 0); ch->size() += phymib_.getHdrLen11(); dh->dh_fc.fc_protocol_version = MAC_ProtocolVersion; dh->dh_fc.fc_type = MAC_Type_Data; dh->dh_fc.fc_subtype = MAC_Subtype_Data; dh->dh_fc.fc_to_ds = 0; dh->dh_fc.fc_from_ds = 0; dh->dh_fc.fc_more_frag = 0; dh->dh_fc.fc_retry = 0; dh->dh_fc.fc_pwr_mgt = 0; dh->dh_fc.fc_more_data = 0; dh->dh_fc.fc_wep = 0; dh->dh_fc.fc_order = 0; /* store data tx time */ ch->txtime() = txtime(ch->size(), dataRate_); Back to send ( ) sendDATA( ) Back to procedure

  6. void Mac802_11::sendRTS(int dst) { Packet *p = Packet::alloc(); hdr_cmn* ch = HDR_CMN(p); struct rts_frame *rf = (struct rts_frame*)p->access(hdr_mac::offset_); assert(pktTx_); assert(pktRTS_ == 0); if( (u_int32_t) HDR_CMN(pktTx_)->size() < macmib_.getRTSThreshold() || (u_int32_t) dst == MAC_BROADCAST) { Packet::free(p); return; } ch->uid() = 0; ch->ptype() = PT_MAC; ch->size() = phymib_.getRTSlen(); ch->iface() = -2; ch->error() = 0; bzero(rf, MAC_HDR_LEN); rf->rf_fc.fc_protocol_version = MAC_ProtocolVersion; rf->rf_fc.fc_type = MAC_Type_Control; rf->rf_fc.fc_subtype = MAC_Subtype_RTS; rf->rf_fc.fc_to_ds = 0; rf->rf_fc.fc_from_ds = 0; rf->rf_fc.fc_more_frag = 0; rf->rf_fc.fc_retry = 0; rf->rf_fc.fc_pwr_mgt = 0; rf->rf_fc.fc_more_data= 0; rf->rf_fc.fc_wep = 0; rf->rf_fc.fc_order = 0; STORE4BYTE(&dst, (rf->rf_ra)); ch->txtime() = txtime(ch->size(), basicRate_ ); STORE4BYTE(&index_, (rf->rf_ta)); rf->rf_duration = usec(phymib_.getSIFS() + txtime(phymib_.getCTSlen(), basicRate_) + phymib_.getSIFS()+ txtime(pktTx_) + phymib_.getSIFS() + txtime(phymib_.getACKlen(), basicRate_)); pktRTS_ = p; } sendRTS( ) Back to send ( ) Back to procedure

  7. deferHandler( ) void Mac802_11::deferHandler() { assert(pktCTRL_ || pktRTS_ || pktTx_); if( check_pktCTRL() == 0) return; assert(mhBackoff_.busy() == 0); if( check_pktRTS() == 0) return; if( check_pktTx() == 0) return; } Back to procedure

  8. Check_pktCTRL() int Mac802_11::check_pktCTRL() { struct hdr_mac802_11 *mh; double timeout; if(pktCTRL_ == 0) return -1; ……………………. } Back to deferHandler() Back to procedure

  9. check_pktRTS() int Mac802_11::check_pktRTS() { struct hdr_mac802_11 *mh; double timeout; assert(mhBackoff_.busy() == 0); if(pktRTS_ == 0) return -1; ………………………………………. } Back to deferHandler() Back to procedure

  10. check_pktTx() Int Mac802_11::check_pktTx() { struct hdr_mac802_11 *mh; double timeout; assert(mhBackoff_.busy() == 0); if(pktTx_ == 0) return -1; mh = HDR_MAC802_11(pktTx_); switch(mh->dh_fc.fc_subtype) { case MAC_Subtype_Data: if(! is_idle()) { sendRTS(ETHER_ADDR(mh->dh_ra)); inc_cw(); mhBackoff_.start(cw_, is_idle()); return 0; } setTxState(MAC_SEND); if((u_int32_t)ETHER_ADDR(mh->dh_ra) != MAC_BROADCAST) timeout = txtime(pktTx_) + DSSS_MaxPropagationDelay + phymib_.getSIFS() + txtime(phymib_.getACKlen(), basicRate_) + DSSS_MaxPropagationDelay; else timeout = txtime(pktTx_); break; default: fprintf(stderr, "check_pktTx:Invalid MAC Control subtype\n"); exit(1); } transmit(pktTx_, timeout); return 0; } Back to deferHandler() Back to procedure

  11. txtime( ) /* * txtime() - calculate tx time for packet of size "psz" bytes * at rate "drt" bps */ double Mac802_11::txtime(double psz, double drt) { double dsz = psz - phymib_.getPLCPhdrLen(); int plcp_hdr = phymib_.getPLCPhdrLen() << 3; int datalen = (int)dsz << 3; double t = (((double)plcp_hdr)/phymib_.getPLCPDataRate()) + (((double)datalen)/drt); return(t); } Back to sendDATA() Back to procedure

  12. inline void Mac802_11::transmit(Packet *p, double timeout) { tx_active_ = 1; if (EOTtarget_) { assert (eotPacket_ == NULL); eotPacket_ = p->copy(); } /* * If I'm transmitting without doing CS, such as when sending an ACK, any incoming packet will be * "missed“ and hence, must be discarded. */ if(rx_state_ != MAC_IDLE) { struct hdr_mac802_11 *dh = HDR_MAC802_11(p); assert(dh->dh_fc.fc_type == MAC_Type_Control); assert(dh->dh_fc.fc_subtype == MAC_Subtype_ACK); assert(pktRx_); struct hdr_cmn *ch = HDR_CMN(pktRx_); ch->error() = 1; /* force packet discard */ } /* * pass the packet on the "interface" which will in turn* place the packet on the channel. * NOTE: a handler is passed along so that the Network Interface can distinguish between incoming * and outgoing packets. */ downtarget_->recv(p->copy(), this); mhSend_.start(timeout); mhIF_.start(txtime(p)); } Back to procedure

  13. When mhSend_ timer expires void Mac802_11::send_timer() { switch(tx_state_) { case MAC_RTS: RetransmitRTS(); break; case MAC_CTS: assert(pktCTRL_); Packet::free(pktCTRL_); pktCTRL_ = 0; break; case MAC_SEND: RetransmitDATA(); break; case MAC_ACK: assert(pktCTRL_); Packet::free(pktCTRL_); pktCTRL_ = 0; break; case MAC_IDLE: break; default: assert(0); } tx_resume(); } Back to transmit() Back to procedure

  14. When mhIF_ timer expires void Mac802_11::txHandler() { if (EOTtarget_) { assert(eotPacket_); EOTtarget_->recv(eotPacket_, (Handler *) 0); eotPacket_ = NULL; } tx_active_ = 0; } Back to transmit() Back to procedure

  15. RetransmitDATA() void Mac802_11::RetransmitDATA() { struct hdr_cmn *ch; struct hdr_mac802_11 *mh; u_int32_t *rcount, thresh; assert(mhBackoff_.busy() == 0); assert(pktTx_); assert(pktRTS_ == 0); ch = HDR_CMN(pktTx_); mh = HDR_MAC802_11(pktTx_); if((u_int32_t)ETHER_ADDR(mh->dh_ra) == MAC_BROADCAST) { Packet::free(pktTx_); pktTx_ = 0; rst_cw(); mhBackoff_.start(cw_, is_idle()); return; } …………………………………………………………… } Back to transmit() Back to procedure

  16. References • mac-802_11.cc, mac-802_11.h • mac-timers.cc, mac-timers.h • http://www.ece.rice.edu/~jpr/ns/docs/802_11.html#DeferTimer

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