[C Network Programming] Stop&Wait ARQ Protocol

/*************************************************************************************/
/*  C program to implement stop and wait protocol*/

#include <conio.h>
#include <dos.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define TIMEOUT 5
#define MAX_SEQ 1
#define TOT_PACKETS 8
#define inc(k) if(k<MAX_SEQ) k++; else k=0;
typedef struct
{
	int data;
}packet;
typedef struct
{
	int kind;
	int seq;
	int ack;
	packet info;
	int err;
}frame;
frame DATA;
typedef enum { frame_arrival, err, timeout, no_event } event_type;

void from_network_layer(packet *);
void to_network_layer(packet *);
void to_physical_layer(frame *);
void from_physical_layer(frame *);
void wait_for_event_sender(event_type *);
void wait_for_event_reciever(event_type *);
void reciever();
void sender();

int i = 1;         //Data to be sent by sender
char turn;      //r , s
int DISCONNECT = 0;
/*__________________________________________________________________________*/
void main()
{
	/*clrscr();*/
	/*randomize();*/
	while (!DISCONNECT)
	{
		sender();
		
		int c = 1, d = 1;
			for (c = 1; c <= 32767; c++)
				for (d = 1; d <= 32767; d++)
				{
				}
		reciever();
	}
	_getch();
}
/*__________________________________________________________________________*/
void sender()
{
	static int frame_to_send = 0;
	static frame s;
	packet buffer;
	event_type event;
	static int flag = 0;

	if (flag == 0)
	{
		from_network_layer(&buffer);
		s.info = buffer;
		s.seq = frame_to_send;
		printf("SENDER :  Info = %d    Seq No = %d     ", s.info, s.seq);
		turn = 'r';
		to_physical_layer(&s);
		flag = 1;
	}
	wait_for_event_sender(&event);
	if (turn == 's')
	{
		if (event == frame_arrival)
		{
			from_network_layer(&buffer);
			inc(frame_to_send);
			s.info = buffer;
			s.seq = frame_to_send;
			printf("SENDER :  Info = %d    Seq No = %d     ", s.info, s.seq);
			turn = 'r';
			to_physical_layer(&s);
		}
		if (event == timeout)
		{
			printf("SENDER : Resending Frame             ");
			turn = 'r';
			to_physical_layer(&s);
		}
	}
}
/*__________________________________________________________________________*/
void reciever()
{
	static int frame_expected = 0;
	frame r, s;
	event_type event;

	wait_for_event_reciever(&event);
	if (turn == 'r')
	{
		if (event == frame_arrival)
		{
			from_physical_layer(&r);
			if (r.seq == frame_expected)
			{
				to_network_layer(&r.info);
				inc(frame_expected);
			}
			else
				printf("RECIEVER : Acknowledgement Resent\n");

			turn = 's';
			to_physical_layer(&s);
		}
		if (event == err)
		{
			printf("RECIEVER : Error Frame\n");
			turn = 's';     //if frame not recieved
		}                 //sender should send it again
	}
}
/*__________________________________________________________________________*/
void from_network_layer(packet *buffer)
{
	(*buffer).data = i;
	i++;
}
/*___________________________________________________________________________*/
void to_physical_layer(frame *s)
{                     // 0 means error
	srand(time(NULL));
	s->err = rand()%4;
	DATA = *s;           //probability of error = 1/4
}
/*___________________________________________________________________________*/
void to_network_layer(packet *buffer)
{
	printf("RECIEVER :Packet %d recieved , Ack Sent\n", (*buffer).data);
	if (i>TOT_PACKETS)          //if all packets recieved then disconnect
	{
		DISCONNECT = 1;
		printf("\nDISCONNECTED");
	}
}
/*___________________________________________________________________________*/
void from_physical_layer(frame *buffer)
{
	*buffer = DATA;
}
/*___________________________________________________________________________*/
void wait_for_event_sender(event_type * e)
{
	static int timer = 0;

	if (turn == 's')
	{
		timer++;
		if (timer == TIMEOUT)
		{
			*e = timeout;
			printf("SENDER : Ack not recieved=> TIMEOUT\n");
			timer = 0;
			return;
		}
		if (DATA.err == 0)
			*e = err;
		else
		{
			timer = 0;
			*e = frame_arrival;
		}
	}
}
/*____________________________________________________________________________*/
void wait_for_event_reciever(event_type * e)
{
	if (turn == 'r')
	{
		if (DATA.err == 0)
			*e = err;
		else
			*e = frame_arrival;
	}
}

 

/*    OUTPUT

SENDER :  Info = 1    Seq No = 0     RECIEVER :Packet 1 recieved , Ack Sent
SENDER : Ack not recieved=> TIMEOUT
SENDER : Resending Frame             RECIEVER : Acknowledgement Resent
SENDER :  Info = 2    Seq No = 1     RECIEVER :Packet 2 recieved , Ack Sent
SENDER :  Info = 3    Seq No = 0     RECIEVER :Packet 3 recieved , Ack Sent
SENDER : Ack not recieved=> TIMEOUT
SENDER : Resending Frame             RECIEVER : Acknowledgement Resent
SENDER :  Info = 4    Seq No = 1     RECIEVER :Packet 4 recieved , Ack Sent
SENDER :  Info = 5    Seq No = 0     RECIEVER :Packet 5 recieved , Ack Sent
SENDER :  Info = 6    Seq No = 1     RECIEVER :Packet 6 recieved , Ack Sent
SENDER :  Info = 7    Seq No = 0     RECIEVER :Packet 7 recieved , Ack Sent
SENDER :  Info = 8    Seq No = 1     RECIEVER : Error Frame
SENDER : Ack not recieved=> TIMEOUT
SENDER : Resending Frame             RECIEVER :Packet 8 recieved , Ack Sent

DISCONNECTED
*/