数据链路层滑动窗口协议的设计与实现源码

#include <stdio.h> #include <string.h> #include "protocol.h" #define MAX_SEQ 15 #define NR_BUFS ((MAX_SEQ+1)/2) #define DATA_TIMER 3000 //帧超时时间间隔 #define ACK_TIMER 240 //ack的超时间隔 struct FRAME { unsigned char kind; unsigned char ack; unsigned char seq; unsigned char data[PKT_LEN]; unsigned int padding; }; int no_nak=1; //标志是否已经发送过nak static int phl_ready = 0; unsigned char oldest_frame=MAX_SEQ+1; static int between(unsigned char a,unsigned char b,unsigned char c) //窗口函数，判断帧号（ack号）是否在窗口内 { if(((a<=b)&&(b<c))||((c<a)&&(a<=b))||((b<c)&&(c<a))) return 1; else return 0; } static void put_frame(unsigned char *frame, int len)//加入校验和crc { *(unsigned int *)(frame + len) = crc32(frame, len); send_frame(frame, len + 4); phl_ready = 0; } static void send_data_frame(unsigned char fk,unsigned char frame_nr,unsigned char frame_expected,unsigned char buffer[NR_BUFS][PKT_LEN]) {//发送数据帧，或ack，或nak struct FRAME s; s.kind = fk; s.seq = frame_nr; s.ack = (frame_expected + MAX_SEQ) % (MAX_SEQ + 1); if(fk==FRAME_DATA) { memcpy(s.data, buffer[frame_nr % NR_BUFS], PKT_LEN);//复制分组到帧内 dbg_frame("Send DATA %d %d, ID %d\n", s.seq, s.ack, *(short *)s.data); put_frame((unsigned char *)&s, 3 + PKT_LEN); //加入校验和 start_timer(frame_nr%NR_BUFS, DATA_TIMER); //启动定时器 } else if(fk == FRAME_NAK) { no_nak=0; //下一次不再发送nak put_frame((unsigned char *)&s, 3); } else if(fk == FRAME_ACK) { dbg_frame("Send ACK %d\n", s.ack); put_frame((unsigned char *)&s, 3); } phl_ready = 0; stop_ack_timer(); //没有必要启动ack定时器 } void main(int argc, char **argv) { int event, arg; struct FRAME f; int len = 0; int i; static unsigned char ack_expected=0, next_frame_to_send=0; static unsigned char frame_expected=0, too_far=NR_BUFS; static unsigned char nbuffered; int arrived[NR_BUFS]; static unsigned char out_buf[NR_BUFS][PKT_LEN], in_buf[NR_BUFS][PKT_LEN]; protocol_init(argc, argv); lprintf("Designed by 成贺睿&魏娜, build: " __DATE__" "__TIME__"\n"); for(i = 0; i < NR_BUFS; i++) //标记接收方的缓冲区是满还是空 arrived[i]=0; enable_network_layer(); while(1) { event = wait_for_event(&arg); switch (event) { case NETWORK_LAYER_READY: nbuffered++; //发送却未被确认的帧数目++ get_packet(out_buf[next_frame_to_send % NR_BUFS]);//得到分组存入缓冲区内 send_data_frame(FRAME_DATA,next_frame_to_send,frame_expected,out_buf); next_frame_to_send=(next_frame_to_send + 1) % ( MAX_SEQ + 1); break; case PHYSICAL_LAYER_READY: phl_ready = 1; break; case FRAME_RECEIVED: len = recv_frame((unsigned char *)&f, sizeof f); if (len < 5 || crc32((unsigned char *)&f, len) != 0) { //校验和出错，就发送nak请求重传 if(no_nak==1) send_data_frame(FRAME_NAK, 0, frame_expected, out_buf); dbg_event("**** Receiver Error, Bad CRC Checksum\n"); break; } if (f.kind == FRAME_DATA) { if((f.seq != frame_expected) && no_nak==1)// 序列号错误 send_data_frame(FRAME_NAK,0, frame_expected, out_buf); else start_ack_timer(ACK_TIMER); if(between(frame_expected, f.seq, too_far)==1&&arrived[f.seq % NR_BUFS] == 0) { dbg_frame("Recv DATA %d %d, ID %d\n", f.seq, f.ack, *(short *)f.data); arrived[f.seq % NR_BUFS] = 1; memcpy(in_buf[f.seq%NR_BUFS], f.data, len-4-3); //把小于当前序列号的帧顺次发送到网络层 while(arrived[frame_expected%NR_BUFS]) { put_packet(in_buf[frame_expected % NR_BUFS], len-7); no_nak=1; arrived[frame_expected%NR_BUFS]=0;//清空缓冲区标志位 frame_expected=(frame_expected+1) % (MAX_SEQ + 1); too_far=(too_far + 1)% (MAX_SEQ + 1);//接收方窗口上限+1 start_ack_timer(ACK_TIMER); } } } if((f.kind==FRAME_NAK)&&between(ack_expected,(f.ack+1) % (MAX_SEQ + 1), next_frame_to_send)==1) { //发送方接到nak,重传丢失（错误）的帧 dbg_frame("Recv NAK %d\n", f.ack); send_data_frame(FRAME_DATA,(f.ack + 1)%(MAX_SEQ+1), frame_expected, out_buf); } while(between(ack_expected,f.ack,next_frame_to_send)==1)//确认帧已经到达 { nbuffered--; stop_timer(ack_expected % NR_BUFS);//关闭帧的定时器 ack_expected=(ack_expected + 1) % (MAX_SEQ + 1); } break; case DATA_TIMEOUT: dbg_event("---- DATA %d timeout\n", arg); send_data_frame(FRAME_DATA,ack_expected, frame_expected, out_buf);//超时后，重传 break; case ACK_TIMEOUT: //无反向数据流，就单独发送ack确认帧 dbg_event("---- ACK %d timeout\n", arg); send_data_frame(FRAME_ACK, 0, frame_expected, out_buf); } if (nbuffered < NR_BUFS && phl_ready) enable_network_layer(); else disable_network_layer(); } }