Stop and Wait 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 message[100]; memcpy(message, input, length); for (j = 0; j < length; j++) { for (i = 0; i <= 7; i++) { temp = (crc >> 15) ^ (message[j] >> 7); crc <<= 1; if (temp) crc ^= 0x1021; message[j] <<= 1; } } //printf("%x",crc); return crc; } #endif

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Source code of UDP Stop and Wait 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, correct_recv = 0; int length = 100; int address_length, text_length; unsigned short sequnce_no; unsigned short server_port = 25000; short socket_file_descriptor; unsigned short crc, recv_crc; char server_ip[] = "127.0.0.1"; char message[1000]; char text_message[100]; char ack_text[] = "ACK"; char nak_text[] = "NAK"; unsigned char Tx_maeesage[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\t 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); if (n != -1) printf("\n\t receive success.....\n"); else printf("\n\t receive failure.....\n"); message[n] = '\0'; printf(" message=%s \n", message); crc = crc_16(message, n); printf(" crc=%x ", crc); memcpy(&sequnce_no, message, sizeof(unsigned short)); memcpy(text_message, message, sizeof(unsigned short)); if (crc == 0) { memcpy(&text_message[2], ack_text, strlen(ack_text)); printf(" %s \n", message); correct_recv++; } else { memcpy(&text_message[2], nak_text, strlen(nak_text)); i = correct_recv; } text_message[2 + strlength(ack_text)] = '\0'; text_length = sizeof(sequnce_no) + strlen(ack_text); m = sendto(socket_file_descriptor, text_message, text_length, 0, (struct sockaddr *) &client_address, sizeof(client_address)); if (m != -1) printf("\n\t send success.....\n"); else printf("\n\t send failure.....\n"); } close(socket_file_descriptor); return 0; }

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Source code of UDP Stop and Wait ARQ Client

#include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <string.h> #include "crc.h" int main() { int socket_file_descriptor, returnvalue, length = 100, n, i; unsigned short sequnce_no = 1, crc, shift_crc; 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]; char rtext[100]; int text_length; struct sockaddr_in server_address; 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); for (i = 1; i < 4; i++) { memcpy(text_message, &sequnce_no, sizeof(sequnce_no)); memcpy(&text_message[2], text[i - 1], 5); crc = crc_16(text_message, sizeof(unsigned short) + strlen(text[i - 1])); shift_crc = crc; shift_crc = (shift_crc << 8) ^ (0x0000); crc = (crc >> 8) ^ (0x0000); crc = (shift_crc) ^ (crc); memcpy(&text_message[7], &crc, sizeof(unsigned short)); text_message[9] = '\0'; text_length = sizeof(sequnce_no) + strlen(text[i - 1]) + sizeof(crc); returnvalue = sendto(socket_file_descriptor, text_message, text_length, 0, (struct sockaddr *) &server_address, sizeof(server_address)); if (returnvalue != -1) printf("\n\t message %d sent successfully.....\n", i); else printf("\n\t message %d sent failure.....\n", i); n = recvfrom(socket_file_descriptor, rtext, length, 0, (struct sockaddr *) &server_address, &address_length); if (n != -1) { rtext[n] = '\0'; if (memcmp(&rtext[2], "ACK", 3) == 0) { printf("\n\t ACK.....\n"); sequnce_no++; sleep(3); } else { i = sequnce_no; printf(" NAK "); sleep(3); } } } close(socket_file_descriptor); return 0; }

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