Go Back n ARQ using C Language

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 length) { unsigned short crc = 0xFFFF; unsigned short temp, i, j; unsigned char msg[100]; memcpy(msg, input, length); for (j = 0; j < length; 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 Go Back n ARQ 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 length = 100; int address_length, text_length; unsigned short seq_no, nack_seq_no = 15; unsigned short server_port = 25000; short socket_file_descriptor; unsigned short crc, recv_crc; char server_ip[] = "127.0.0.1"; char message[1000] = "ghgsdhsvgdghasdadafh"; char text_message[100]; char ack_text[] = "ACK"; char nak_text[] = "NAK"; unsigned char text_message[100]; char *client; struct sockaddr_in server_address, client_address; client = (char *) malloc(sizeof(server_address)); socket_file_descriptor = socket(AF_INET, SOCK_DGRAM, 0); if (socket_file_descriptor < 0) { printf("failed"); exit(0); } printf("\n socket created.....\n"); bzero(&server_address, sizeof(server_address)); server_address.sin_family = AF_INET; inet_aton(server_ip, &server_address.sin_addr); server_address.sin_port = htons(server_port); bind(socket_file_descriptor, (struct sockaddr *) &server_address, sizeof(server_address)); while (1) { n = recvfrom(socket_file_descriptor, message, length, 0, (struct sockaddr *) &client_address, &address_length); memcpy(&seq_no, message, sizeof(unsigned short)); memcpy(text_message, message, sizeof(unsigned short)); message[n] = '\0'; printf("\n %s \n", message); crc = crc_16(message, n); printf("\n crc=%x \n", crc); //sleep(5); if (nack_seq_no >= seq_no) { if (crc == 0) { memcpy(&text_message[2], ack_text, strlen(ack_text)); correct_recv++; nack_seq_no = 15; printf("\n ack for %d\n", seq_no); } else { memcpy(&text_message[2], nak_text, strlen(nak_text)); nack_seq_no = seq_no; printf("\n nack for %d\n", seq_no); //i=correct_recv; } text_message[2 + strlen(ack_text)] = '\0'; text_length = sizeof(seq_no) + strlen(ack_text); m = sendto(socket_file_descriptor, text_message, 5, 0, (struct sockaddr *) &client_address, sizeof(client_address)); if (m!=-1) printf("\n send success.....\n"); else printf("\n send failure.....\n"); } if (correct_recv == 3) break; } close(socket_file_descriptor); return 0; }

Source code of UDP Go Back n ARQ 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); int socket_file_descriptor, returnvalue, length = 100, n, i = 1, j = 1; unsigned short seq_no = 1, seq_no_ret, crc, shift_crc, correct_recv = 0; unsigned int address_length; unsigned short server_port = 25000; char server_ip[] = "127.0.0.1"; char *text[3] = { "abcde", "fghij", "klmno" }; unsigned char text_message[100]; unsigned char text_message_copy[100]; char rtext[100]; int text_length; struct sockaddr_in server_address; int main() { int val; address_length = sizeof(server_address); bzero(&server_address, sizeof(server_address)); server_address.sin_family = AF_INET; server_address.sin_port = htons(server_port); inet_aton(server_ip, &server_address.sin_addr); socket_file_descriptor = socket(PF_INET, SOCK_DGRAM, 0); val = fcntl(socket_file_descriptor, F_GETFL, 0); fcntl(socket_file_descriptor, F_SETFL, val | O_NONBLOCK | O_ASYNC); fcntl(socket_file_descriptor, F_SETOWN, getpid()); signal(SIGIO, sig_io); while (1) { if (seq_no <= 3) { printf(" seq_no=%d\n", seq_no); memcpy(text_message, &seq_no, sizeof(seq_no)); memcpy(&text_message[2], text[seq_no - 1], 5); memcpy(text_message_copy, text_message, 7); crc = crc_16(text_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(&text_message[7], &crc, sizeof(unsigned short)); text_message[9] = '\0'; text_length = sizeof(seq_no) + strlen(text[seq_no - 1]) + sizeof(crc); returnvalue = sendto(socket_file_descriptor, text_message, text_length, 0, (struct sockaddr *) &server_address, sizeof(server_address)); seq_no++; if(returnvalue!=-1) printf("\n\t message %d sent successfully.....\n",i); else printf("\n\t message %d sent failure.....\n",i); } else { if (correct_recv == 3) break; else continue; } } close(socket_file_descriptor); return 0; } static void sig_io(int signo) { n = recvfrom(socket_file_descriptor, rtext, length, 0, (struct sockaddr *) &server_address, &address_length); 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++; sleep(3); } else { seq_no = seq_no_ret; printf("\n NAK for %d\n", seq_no); sleep(3); } } }

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