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How to Send a Unicast Packet in Networking Protocol

This guide outlines the procedure for sending a unicast packet within networking protocols, specifically following the path of communication with multiple steps. It covers the key functions involved such as recv(), send(), sendDATA(), sendRTS(), and their respective transitions. By understanding the sequence and timing mechanisms, including deferring handlers and checking packet conditions, users can effectively manage packet transmissions. Additionally, it details how control frames like RTS (Request to Send) and CTS (Clear to Send) are handled, ensuring reliable packet delivery in a network environment.

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How to Send a Unicast Packet in Networking Protocol

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  1. How to send a unicast packet?

  2. Procedure Roughly takes the following path (when no errors or congestion): recv() -> send() -> sendDATA() and sendRTS() -> start defer timer -> deferHandler() -> check_pktRTS() -> transmit() -> recv() -> receive timer started -> recv_timer() -> recvCTS() -> tx_resume() -> start defer timer -> rx_resume() -> deferHandler() -> check_pktTx() -> transmit() -> recv() -> receive timer started -> recv_timer() -> recvACK() -> tx_resume() -> callback_ -> rx_resume() -> 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; } if(tx_active_ && hdr->error() == 0) { hdr->error() = 1; } if(rx_state_ == MAC_IDLE) { setRxState(MAC_RECV); pktRx_ = p; mhRecv_.start(txtime(p)); } else { ……………………………………………………………………………………… } } 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; mh = HDR_MAC802_11(pktRTS_); switch(mh->dh_fc.fc_subtype) { case MAC_Subtype_RTS: if(! is_idle()) { inc_cw(); mhBackoff_.start(cw_, is_idle()); return 0; } setTxState(MAC_RTS); timeout = txtime(phymib_.getRTSlen(), basicRate_) + DSSS_MaxPropagationDelay + phymib_.getSIFS()+ txtime(phymib_.getCTSlen(), basicRate_)+ DSSS_MaxPropagationDelay; break; default: fprintf(stderr, "check_pktRTS:Invalid MAC Control subtype\n"); exit(1); } transmit(pktRTS_, timeout); return 0; } 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. 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 recv_timer() Back to procedure

  12. Void Mac802_11::recv_timer() { …………………. switch(type) { case MAC_Type_Management: ……………………………………… goto done; case MAC_Type_Control: switch(subtype) { case MAC_Subtype_RTS: recvRTS(pktRx_); break; case MAC_Subtype_CTS: recvCTS(pktRx_); break; case MAC_Subtype_ACK: recvACK(pktRx_); break; default: ………………………………………… } break; case MAC_Type_Data: switch(subtype) { case MAC_Subtype_Data: recvDATA(pktRx_); break; default: fprintf(stderr, "recv_timer2:Invalid MAC Data Subtype %x\n", subtype); exit(1); } break; default: fprintf(stderr, "recv_timer3:Invalid MAC Type %x\n", subtype); exit(1); } done: pktRx_ = 0; rx_resume(); } recv_timer() Back to procedure

  13. } else if(pktTx_) { if (mhBackoff_.busy() == 0) { hdr_cmn *ch = HDR_CMN(pktTx_); struct hdr_mac802_11 *mh = HDR_MAC802_11(pktTx_); if ((u_int32_t) ch->size() < macmib_.getRTSThreshold() || (u_int32_t) ETHER_ADDR(mh->dh_ra) == MAC_BROADCAST) { rTime = (Random::random() % cw_) * phymib_.getSlotTime(); mhDefer_.start(phymib_.getDIFS() + rTime); } else { mhDefer_.start(phymib_.getSIFS()); } } } else if(callback_) { Handler *h = callback_; callback_ = 0; h->handle((Event*) 0); } setTxState(MAC_IDLE); } void Mac802_11::tx_resume() { double rTime; assert(mhSend_.busy() == 0); assert(mhDefer_.busy() == 0); if(pktCTRL_) { mhDefer_.start(phymib_.getSIFS()); } else if(pktRTS_) { if (mhBackoff_.busy() == 0) { rTime = (Random::random() % cw_) * phymib_.getSlotTime(); mhDefer_.start( phymib_.getDIFS() + rTime); } tx_resume() Back to recvCTS Back to recvACK Back to procedure

  14. rx_resume( ) Void Mac802_11::rx_resume() { assert(pktRx_ == 0); assert(mhRecv_.busy() == 0); setRxState(MAC_IDLE); } Back to recv_timer Back to procedure

  15. recvCTS( ) Void Mac802_11::recvCTS(Packet *p) { if(tx_state_ != MAC_RTS) { discard(p, DROP_MAC_INVALID_STATE); return; } assert(pktRTS_); Packet::free(pktRTS_); pktRTS_ = 0; assert(pktTx_); mhSend_.stop(); /* * The successful reception of this CTS packet implies * that our RTS was successful. * According to the IEEE spec 9.2.5.3, you must * reset the ssrc_, but not the congestion window. */ ssrc_ = 0; tx_resume(); mac_log(p); } Back to recv_timer() Back to procedure

  16. recvACK( ) Void Mac802_11::recvACK(Packet *p) { struct hdr_cmn *ch = HDR_CMN(p); if(tx_state_ != MAC_SEND) { discard(p, DROP_MAC_INVALID_STATE); return; } assert(pktTx_); mhSend_.stop(); if((u_int32_t) HDR_CMN(pktTx_)->size() <= macmib_.getRTSThreshold()) ssrc_ = 0; else slrc_ = 0; rst_cw(); Packet::free(pktTx_); pktTx_ = 0; assert(mhBackoff_.busy() == 0); mhBackoff_.start(cw_, is_idle()); tx_resume(); mac_log(p); } Back to recv_timer() Back to procedure

  17. 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 check_pktRTS() Back to procedure

  18. 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

  19. 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

  20. 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

  21. 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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