cn_5.cpp

/*
  Selective repeat sliding window protocol
*/

#include<iostream>
#include<cstdlib>
#include<ctime>
#include<cmath>
using namespace std;

#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 receiver(int);

};

void sel_repeat::input()
{

    int n;     //no. of bits for the frame
    int m;    //no. of frames from n bits
    int i;
    cout<<"\nEnter the no. of bits for the sequence no. : ";
    cin>>n;
    m=pow(2,n);

    int t=0;

fr_send_at_instance=(m/2);

for(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<<"\nSENDER : Frame "<<send[i]<<" is sent\n";

}

receiver(m);

}

void sel_repeat::receiver(int m)

{

time_t t;

int f;
int j;
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 f=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<<"\nreciever:Frame "<<rcvd[j]<< "recieved correctly\n";

rcvd[j]=arr[rw];

rw=(rw+1)%m;

break;

}
int j;
if(j==fr_send_at_instance)

cout<<"\nreciever:Duplicate frame "<<send[i]<<" discarded\n";

a1=rand()%5;

//if al==3 then ack is lost

//else recieved

if(a1==3)

{

cout<<"\n(acknowledgement "<<send[i]<<" lost)\n";

cout<<"\n(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<<"\nRECEIVER : Frame "<<send[i]<<" is damaged\n";

cout<<"\nRECEIVER : Negative Acknowledgement "<<send[i]<<" sent\n";

}

else

{

cout<<"\nRECEIVER : Frame "<<send[i]<<" is lost\n";

cout<<"\n (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;

}

int 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<<"\nWant to continue('Y' or 'y' to continue): ";
cin>>ch;
cout<<"\n";
if(ch=='y')
   sender(m);
else
   exit(0);
}

int main()
{
  sel_repeat sr;;
  sr.input();

  return 0;
}