StopAndWait.c

#include <stdio.h>
#include <stdlib.h>

struct frame {
    int info;
    int seq;
};

int ak;
int t = 5, k;
int disconnect = 0;
struct frame p;
char turn = 's';     // Initialize first turn as sender
int errorframe = 1;  // no Error
int errorack = 1;

void sender();
void receiver();

void main() {
    p.info = 0; // data part
    p.seq = 0;  // sequence number

    while (!disconnect) {
        sender(); // call sender

        for (k = 1; k <= 10000000; k++)
            ;
        // After a finite amount of time call receiver
        receiver();
    }
}

void sender() {
    static int flag = 0;

    if (turn == 's') { // sender turn
        if (errorack == 0) {  // Ack didn't arrive
            printf("SENDER: sent packet with seq NO:%d\n", p.seq);
            errorframe = rand() % 4; // randomly pick Error frame as 4
            printf("%s\n", (errorframe == 0 ? "Error While sending Packet" : ""));
            turn = 'r';
        } else {
            if (flag == 1)
                printf("SENDER: Received ACK for packet %d\n", ak);
            if (p.seq == 5) {
                disconnect = 1;
                return;
            }

            p.info = p.info + 1;
            p.seq = p.seq + 1;

            printf("SENDER: sent packet with seq NO:%d\n", p.seq);
            errorframe = rand() % 4;
            printf("%s\n", (errorframe == 0 ? "Error While sending Packet" : ""));

            turn = 'r';
            flag = 1;
        }
    } else {
        t--;
        printf("SENDER time reducing\n");

        if (t == 0) {
            turn = 's';
            errorack = 0;
            t = 5;
        }
    }
}

void receiver() {
    static int frexp = 1;

    if (turn == 'r') {
        if (errorframe != 0) {
            if (p.seq == frexp) {  // if frame sequence number is eq to frexp
                printf("RECEIVER: Received packet with seq %d\n", p.seq);

                // note sequence number of frame arrived
                // to send acknowledgement
                ak = p.seq;

                // increment the frame sequence number
                frexp = frexp + 1;

                // Set next turn as sender
                turn = 's';

                // Send acknowledgement error for frame number 4
                errorack = rand() % 4;
                printf("%s\n", (errorack == 0 ? "Error While sending ACK" : ""));
            } else {
                // Receiver received Duplicated frame for lost frame after Resending
                printf("RECEIVER: Duplicated packet with seq %d\n", frexp - 1);

                // Note down acknowledgement number of frame
                ak = frexp - 1;

                // next turn sender
                turn = 's';

                errorack = rand() % 4;
                printf("%s\n", (errorack == 0 ? "Error While sending ACK" : ""));
            }
        }
    }
}