Source code of CRC
#ifndef CRCH
#define CRCH
unsigned short crc_16(unsigned char[100], unsigned short);
unsigned short crc_16(unsigned char input[100], unsigned short len)
{
unsigned short crc = 0xFFFF;
unsigned short temp, i, j;
unsigned char msg[100];
memcpy(msg, input, len);
for (j = 0; j < len; j++)
{
for (i = 0; i <= 7; i++)
{
temp = (crc >> 15) ^ (msg[j] >> 7);
crc <<= 1;
if (temp)
{
crc ^= 0x1021;
}
msg[j] <<= 1;
}
}
return crc;
}
#endif
Source code of UDP Selective Repeat Server
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include "crc.h"
int main()
{
short int n = 0, m = 0, i = 1, correct_recv = 0;
int len = 100;
int addrlen, Tx_len;
unsigned short seq_no, nack_seq_no = 15;
unsigned short serv_port = 25000;
short sockfd;
unsigned short crc, recv_crc;
char serv_ip[] = "127.0.0.1";
char mesg[1000];
char Tx_message[100];
char ack[] = "ACK";
char nak[] = "NAK";
unsigned char Tx_maeesage[100];
char *client;
int ksd;
struct sockaddr_in servaddr, clientaddr;
client = (char *) malloc(sizeof(servaddr));
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (sockfd < 0)
{
printf("failed");
exit(0);
}
printf("\n\t socket created.....\n");
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
ksd = inet_aton(serv_ip, &servaddr.sin_addr);
printf("%d", ksd);
servaddr.sin_port = htons(serv_port);
bind(sockfd, (struct sockaddr *) &servaddr, sizeof(servaddr));
while (1)
{
n = recvfrom(sockfd, mesg, len, 0, (struct sockaddr *) &clientaddr, &addrlen);
memcpy(&seq_no, mesg, sizeof(unsigned short));
memcpy(Tx_message, mesg, sizeof(unsigned short));
mesg[n] = '\0';
printf("\n %s \n", mesg);
crc = crc_16(mesg, n);
printf("\n crc=%x \n", crc);
//sleep(5);
if (seq_no <= 3)
{
if (crc == 0)
{
memcpy(&Tx_message[2], ack, strlen(ack));
correct_recv++;
printf("\n\t\t\t ack for %d\n", seq_no);
}
else
{
memcpy(&Tx_message[2], nak, strlen(nak));
printf("\n\t\t\t nack for %d\n", seq_no);
//i=correct_recv;
}
Tx_message[2 + strlen(ack)] = '\0';
Tx_len = sizeof(seq_no) + strlen(ack);
m = sendto(sockfd, Tx_message, Tx_len, 0, (struct sockaddr *) &clientaddr, sizeof(clientaddr));
if (m!=-1)
printf("\n\t send success.....\n");
else
printf("\n\t send failure.....\n");
}
if (correct_recv == 3)
break;
}
close(sockfd);
}
Source code of UDP Selective Repeat Client
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <signal.h>
#include "crc.h"
static void sig_io(int);
enum
{
false, true
} flag;
int sockfd, returnvalue, len = 100, n, i = 1, j = 1, k = 1;
unsigned short seq_no = 1, seq_no_ret, crc, shift_crc, correct_recv = 0;
unsigned short error_seq_no = 15;
unsigned int addrlen;
unsigned short serv_port = 25000;
char serv_ip[] = "127.0.0.1";
char *text[3] = { "abcde", "fghij", "klmno" };
unsigned char Tx_message[100];
unsigned char Tx_message_copy[100];
char rtext[100];
int Tx_len;
struct sockaddr_in servaddr;
int main() {
int val;
addrlen = sizeof(servaddr);
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(serv_port);
inet_aton(serv_ip, &servaddr.sin_addr);
sockfd = socket(PF_INET, SOCK_DGRAM, 0);
val = fcntl(sockfd, F_GETFL, 0);
fcntl(sockfd, F_SETFL, val | O_NONBLOCK | O_ASYNC);
fcntl(sockfd, F_SETOWN, getpid());
signal(SIGIO, sig_io);
flag = false;
while (1)
{
if (seq_no <= 3 && (flag == false))
{
printf(" seq_no=%d\n", seq_no);
memcpy(Tx_message, &seq_no, sizeof(seq_no));
memcpy(&Tx_message[2], text[seq_no - 1], 5);
memcpy(Tx_message_copy, Tx_message, 7);
crc = crc_16(Tx_message_copy, sizeof(unsigned short) + strlen(text[seq_no - 1]));
shift_crc = crc;
shift_crc = (shift_crc << 8) ^ (0x0000);
crc = (crc >> 8) ^ (0x0000);
crc = (shift_crc) ^ (crc);
if (seq_no == 2 && j == 1)
{
crc = 0x5555;
j++;
}
memcpy(&Tx_message[7], &crc, sizeof(unsigned short));
Tx_message[9] = '\0';
Tx_len = sizeof(seq_no) + strlen(text[seq_no - 1]) + sizeof(crc);
returnvalue = sendto(sockfd, Tx_message, Tx_len, 0, (struct sockaddr *) &servaddr, sizeof(servaddr));
seq_no++;
/*
if(returnvalue!=-1)
{
printf("\n\t message %d sent successfully.....\n",i);
i++;
}
else
printf("\n\t message %d sent failure.....\n",i);
*/
}
else if (flag == true)
{
memcpy(Tx_message, &error_seq_no, sizeof(error_seq_no));
memcpy(&Tx_message[2], text[error_seq_no - 1], 5);
memcpy(Tx_message_copy, Tx_message, 7);
crc = crc_16(Tx_message_copy, sizeof(unsigned short) + strlen(text[error_seq_no - 1]));
shift_crc = crc;
shift_crc = (shift_crc << 8) ^ (0x0000);
crc = (crc >> 8) ^ (0x0000);
crc = (shift_crc) ^ (crc);
memcpy(&Tx_message[7], &crc, sizeof(unsigned short));
Tx_message[9] = '\0';
Tx_len = sizeof(error_seq_no) + strlen(text[error_seq_no - 1]) + sizeof(crc);
returnvalue = sendto(sockfd, Tx_message, Tx_len, 0, (struct sockaddr *) &servaddr, sizeof(servaddr));
flag = false;
}
else
{
if (correct_recv == 3)
break;
else
continue;
}
}
close(sockfd);
return 0;
}
static void sig_io(int signo)
{
n = recvfrom(sockfd, rtext, len, 0, (struct sockaddr *) &servaddr, &addrlen);
if (n != -1)
{
rtext[n] = '\0';
memcpy(&seq_no_ret, rtext, sizeof(unsigned short));
if (memcmp(&rtext[2], "ACK", 3) == 0)
{
printf("\n ACK for %d\n", seq_no_ret);
correct_recv++;
flag = false;
//sleep(3);
}
else
{
error_seq_no = seq_no_ret;
flag = true;
printf("\n NAK for %d\n", error_seq_no);
//sleep(3);
}
}
}
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