SELECTIVE REPEAT PROTOCOL PROGRAM IN C++

// SIMULATE SELECTIVE REPEAT PROTOCOL

# include <iostream.h>
# include <conio.h>
# include <stdlib.h>
# include <time.h>
# include <math.h>

# define TOT_FRAMES 500
# define FRAMES_SEND 10

class sel_repeat
{
 private:
  int fr_send_at_instance;
  int arr[TOT_FRAMES];
  int send[FRAMES_SEND];
  int rcvd[FRAMES_SEND];
  char rcvd_ack[FRAMES_SEND];
  int sw;
  int rw; // tells expected frame
 public:
  void input();
  void sender(int);
  void reciever(int);
};

void sel_repeat :: input()
{
 int n;  // no of bits for the frame
 int m;  // no of frames from n bits

 cout << "Enter the no of bits for the sequence number ";
 cin >> n;

 m = pow (2 , n);

 int t = 0;

 fr_send_at_instance = (m / 2);

 for (int i = 0 ; i < TOT_FRAMES ; i++)
 {
  arr[i] = t;
  t = (t + 1) % m;
 }

 for (i = 0 ; i < fr_send_at_instance ; i++)
 {
  send[i] = arr[i];
  rcvd[i] = arr[i];
  rcvd_ack[i] = 'n';
 }

 rw = sw = fr_send_at_instance;

 sender(m);
}

void sel_repeat :: sender(int m)
{
 for (int i = 0 ; i < fr_send_at_instance ; i++)
 {
  if ( rcvd_ack[i] == 'n' )
   cout << " SENDER   : Frame " << send[i] << " is sent\n";
 }
 reciever (m);
}

void sel_repeat :: reciever(int m)
{
 time_t t;
 int f;
 int f1;
 int a1;
 char ch;

 srand((unsigned) time(&t));

 for (int i = 0 ; i < fr_send_at_instance ; i++)
 {
  if (rcvd_ack[i] == 'n')
  {
   f = rand() % 10;

   // if = 5 frame is discarded for some reason
   // else frame is correctly recieved

   if (f != 5)
   {
    for (int j = 0 ; j < fr_send_at_instance ; j++)

     if (rcvd[j] == send[i])
     {
      cout << "RECIEVER : Frame " << rcvd[j] << " recieved correctly\n";
      rcvd[j] = arr[rw];
      rw = (rw + 1) % m;
      break;
     }

    if (j == fr_send_at_instance)
     cout << "RECIEVER : Duplicate frame " << send[i] << " discarded\n";

    a1 = rand() % 5;

     // if a1 == 3 then ack is lost
     //            else recieved

    if (a1 == 3)
    {
     cout << "(Acknowledgement " << send[i] << " lost)\n";
     cout << " (SENDER TIMEOUTS --> RESEND THE FRAME)\n";
     rcvd_ack[i] = 'n';
    }
    else
    {
     cout << "(Acknowledgement " << send[i] << " recieved)\n";
     rcvd_ack[i] = 'p';
    }
   }
   else
   {
    int ld = rand() % 2;

    // if = 0 then frame damaged
    // else frame lost

    if (ld == 0)
    {
     cout << "RECIEVER : Frame " << send[i] << " is damaged\n";
     cout << "RECIEVER : Negative acknowledgement " << send[i]  << " sent\n";
    }
    else
    {
     cout << "RECIEVER : Frame " << send[i] << " is lost\n";
     cout << " (SENDER TIMEOUTS --> RESEND THE FRAME)\n";
    }
    rcvd_ack[i] = 'n';
   }
  }
 }

 for ( int j = 0 ; j < fr_send_at_instance ; j++)
 {
  if (rcvd_ack[j] == 'n')
   break;
 }

 i = 0 ;

 for (int k = j ; k < fr_send_at_instance ; k++)
 {
  send[i] = send[k];

  if (rcvd_ack[k] == 'n')
   rcvd_ack[i] = 'n';
  else
   rcvd_ack[i] = 'p';

  i++;
 }

 if ( i != fr_send_at_instance )
 {
  for ( int k = i ; k < fr_send_at_instance ; k++)
  {
   send[k] = arr[sw];
   sw = (sw + 1) % m;
   rcvd_ack[k] = 'n';
  }
 }
 cout << "Want to continue...";
 cin >> ch;
 cout << "\n";

 if (ch == 'y')
  sender(m);
 else
  exit(0);
}

void main()
{
 clrscr();
 sel_repeat sr;
 sr.input();
 getch();
}


/*              OUTPUT

Enter the no of bits for the sequence number 6
 SENDER   : Frame 24 is sent
 SENDER   : Frame 32 is sent
 SENDER   : Frame 32 is sent
 SENDER   : Frame 27 is sent
 SENDER   : Frame 28 is sent
 SENDER   : Frame 29 is sent
 SENDER   : Frame 30 is sent
 SENDER   : Frame 31 is sent
RECIEVER : Frame 24 is lost
 (SENDER TIMEOUTS --> RESEND THE FRAME)
RECIEVER : Frame 32 recieved correctly
(Acknowledgement 32 recieved)
RECIEVER : Frame 33 recieved correctly
(Acknowledgement 34 recieved)
RECIEVER : Frame 27 recieved correctly
(Acknowledgement 34 recieved)
RECIEVER : Frame 28 is damaged
RECIEVER : Negative acknowledgement 28 sent
RECIEVER : Frame 29 recieved correctly
(Acknowledgement 35 recieved)
RECIEVER : Frame 30 recieved correctly
(Acknowledgement 36 lost)
 (SENDER TIMEOUTS --> RESEND THE FRAME)
RECIEVER : Frame 31 recieved correctly
(Acknowledgement 37 recieved)
Want to continue...n

*/