1 void
 2 Mac802_11::recv(Packet *p, Handler *h)
 3 {
 4     struct hdr_cmn *hdr = HDR_CMN(p);
 5     /*
 6      * Sanity Check
 7      */
 8     assert(initialized());
 9
10     /*
11      *  Handle outgoing packets.
12      */
13     if(hdr->direction() == hdr_cmn::DOWN) {//向下传输，也就是节点要向外发送，故调用recv（）
14                 send(p, h);
15         16                 return;
17         }
18     /*
19      *  Handle incoming packets.
20      *
21      *  We just received the 1st bit of a packet on the network
22      *  interface.
23      *
24      */
25
26     /*
27      *  If the interface is currently in transmit mode, then
28      *  it probably won't even see this packet.  However, the
29      *  "air" around me is BUSY so I need to let the packet
30      *  proceed.  Just set the error flag in the common header
31      *  to that the packet gets thrown away.
32      */
33     if(tx_active_ && hdr->error() == 0) {//如果当前正在发送的话则标记为错误，这个数据包会在后面的函数中被处理掉
34         hdr->error() = 1;
35     }
36
37     if(rx_state_ == MAC_IDLE) {//如果当前空闲则设置为接收态
38         setRxState(MAC_RECV);
39         pktRx_ = p;
40         /*
41          * Schedule the reception of this packet, in
42          * txtime seconds.
43          */
44         if (mhProbe_.busy() && OnMinChannelTime) {
45             Recv_Busy_ = 1;  // Receiver busy indication for Probe Timer
46         }
47
48    49         mhRecv_.start(txtime(p));
50     } else {
51         /*
52          *  If the power of the incoming packet is smaller than the
53          *  power of the packet currently being received by at least
54                  *  the capture threshold, then we ignore the new packet.
55          */
56         if(pktRx_->txinfo_.RxPr / p->txinfo_.RxPr >= p->txinfo_.CPThresh) {//有冲突发生时，如果新到的包功率比较小，信噪比在阀值以下的时候调用capture函数，主要作用是
57             capture(p);
58         } else {//冲突比较大的时候需要调用冲突函数
59             collision(p);
60         }
61     }

 1 void
 2 Mac802_11::capture(Packet *p)
 3 {
 4     /*
 5      * Update the NAV so that this does not screw
 6      * up carrier sense.
 7      */
 8     set_nav(usec(phymib_.getEIFS() + txtime(p)));
 9     Packet::free(p);
10 }

 1 void
 2 Mac802_11::collision(Packet *p)
 3 {
 4     switch(rx_state_) {
 5     case MAC_RECV:
 6         setRxState(MAC_COLL);
 7         /* fall through */
 8     case MAC_COLL:
 9         assert(pktRx_);
10         assert(mhRecv_.busy());
11         /*
12          *  Since a collision has occurred, figure out
13          *  which packet that caused the collision will
14          *  "last" the longest.  Make this packet,
15          *  pktRx_ and reset the Recv Timer if necessary.
16          */
17         if(txtime(p) > mhRecv_.expire()) {
18             mhRecv_.stop();
19             discard(pktRx_, DROP_MAC_COLLISION);
20             pktRx_ = p;
21             mhRecv_.start(txtime(pktRx_));
22         }
23         else {
24             discard(p, DROP_MAC_COLLISION);
25         }
26         break;
27     default:
28         assert(0);
29     }
30 ｝