NS2_mac层理解.doc

NS2 mac层理解 mac-802_11.h:// frame control field:struct frame_control {u_char??? ??? fc_subtype??? ??? : 4;u_char??? ??? fc_type??? ??? ??? : 2;?? //frame type : RTS, CTS, ACK, datau_char??? ??? fc_protocol_version??? : 2;u_char??? ??? fc_order??? ??? : 1;u_char??? ??? fc_wep??? ??? ??? : 1;u_char??? ??? fc_more_data??? ??? : 1;u_char??? ??? fc_pwr_mgt??? ??? : 1;u_char??? ??? fc_retry??? ??? : 1;u_char??? ??? fc_more_frag??? ??? : 1;u_char??? ??? fc_from_ds??? ??? : 1;u_char??? ??? fc_to_ds??? ??? : 1;};// frame field:struct hdr_mac802_11 {struct frame_control??? dh_fc;//duration of reserved transmission time (RTS/CTS)u_int16_t??? ??? dh_duration;//address 1: MAC address of wireless host or AP to receive this frameu_char??????????? dh_ra[ETHER_ADDR_LEN];//MAC address of wireless host or AP transmitting this frameu_char??????????? dh_ta[ETHER_ADDR_LEN];//MAC address of router interface to which AP is attachedu_char??????????? dh_3a[ETHER_ADDR_LEN];//used only in ad hoc modeu_char??? ??? ??? dh_4a[ETHER_ADDR_LEN];u_int16_t??? ??? dh_scontrol;u_char??? ??? ??? dh_body[1]; // size of 1 for ANSI compatibility};发送包：recv()--send()--sendDATA() and sendRTS()--start defer timer--deferHandler()--check_pktRTS()--transmit()--recv()--recieve timer started--recv_timer()--recvCTS()--tx_resume()--start defer timer--rx_resume()--deferHandler()--check_pktTx()--transmit()--recv()--recieve timer started--recv_timer()--recvACK()--tx_resume()--callback_--rx_resume() recv()(down)--要发送的数据包先被recv()处理，recv()先检查包头方向字段，如果是down,意味着包来自上层，数据包将转由send()处理。不管接收包来自上层或下层，recv()总被调用。 send()-- 首先检查能量模式，如果在睡眠模式则丢弃包，并随包设callback_ 给handler(?)，这是包传送完毕后会调用handler的原因。 下一步，send()调用sendDATA()and sendRTS建立数据包包头，RTS包存储在pktTx_ and pktRTS_并随数据包发送。数据包的MAC头赋唯一序列值。 MAC用 is_idle()检查backoff timer,如果backoff timer不减少，则检查信道（medium)是否空闲，如果空闲则启动defer. DIFS＋a randomly chosen amount of time in the interval [0,cw_), cw_当前竞争窗口。 如果节点正在等待其defer time，则继续等待。 如果介质忙，节点启动其backoff timer. 此时，send