模仿数据链路层的
gobackn协议
/*该
协议是搭载ack的回退n步
协议*/
#include
#include "protocol.h"
#define max_seq 7
#define flag 126
#define ESC 100
#define wait_time 2700 //发送计时器等待的时间
#define ack_wait_time 280
static int phl_ready = 0;
unsigned char buf[max_seq+1][270];
unsigned char ack[8]; //发送空的ack帧
unsigned char in_buf[600], last_buf[520];//接收时的缓冲区;去掉冗余之后的缓冲区,为防备因误码两帧合并为一帧而定义了很大一个数组
int nbuffered=0; //发送的帧数
int buf_size[max_seq+1]; //记下以发送各帧的帧长
int next_frame_to_send=0;
int frame_in_phl=0; //用于成帧
int frame_expected=0;
int ack_expected=0;
int between
(int a,int b,int c
)
{
if
( ((a<=b
)&&
(b<c
)) ||
((c<a
)&&
(a<=b
)) ||
((b<c
)&&
(c<a
)) )
return 1;
else return 0;
}
//判断帧尾,防止出现误判esc esc flag为数据的情况
int end_flag
(int in_len
)
{
int count=0;
int i;
if
(in_len=0;i--
)//记录flag前的esc数目
count++;
return count%2; //若flag前的esc为偶数，则为帧尾
}//成帧函数--数据帧
void send_frame
(char *my_buf,int len
)
{
int n;
buf[frame_in_phl][0]=
(frame_expected+max_seq
)%
(max_seq+1
); //ack
buf[frame_in_phl][1]=frame_in_phl; //发送帧的帧号
for
(n=0;n<len;n++
)
buf[frame_in_phl][n+2]=my_buf[n]; //将处理过的新帧赋值到缓冲区中
len=len+2;
*
(unsigned int *
)(buf[frame_in_phl]+len
) = crc32
(buf[frame_in_phl],len
); //在原始帧的基础上加检验
和
buf_size[frame_in_phl]=len+4; //记录当前帧的长度,包括3个帧头，4个检验
和
nbuffered=nbuffered+1; //缓冲区占用数加一
frame_in_phl=
(frame_in_phl+1
)%
(max_seq+1
);
}
//成帧函数--ack帧
void send_ack
() //ack帧的处理
{
ack[0]=
(frame_expected+max_seq
)%
(max_seq+1
);
ack[1]=max_seq+10; //ack帧的序号位，使ack[1]==frame_expected恒不成立
*
(unsigned int *
)(ack+2
) = crc32
(ack,2
); //在原始帧的基础上加检验
和
}
//主函数
int main
(int argc, char **argv
)
{
int event, arg, n , m , i , j , len = 0 ,in_len = 0;
unsigned char my_buf[260];
int phl_wait=0; //在物理层中还没有被发送的帧
protocol_init
(argc, argv
);
enable_network_layer
();
for
(;;
) {
event = wait_for_event
(&arg
);
switch
(event
) {
case NETWORK_LAYER_READY:
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