// Algorithm for Sender of Stop and Wait



// This could be implemented as a thread or daemon



// that is always running







Inputs:



	RTT - The RTT of the link



	packet_queue - this a queue where network layer puts packets to send







void Sender(int RTT, Queue packet_queue){



     frame next_frame = new frame(), read_frame = new frame();



     int next_seq_no = 0;



     Packet next_p; 



     long wait_time = 0;



     int result = 0;



     bool do_send = true;



     // set timer to 1.5 RTT



     wait_time = 1.5 * RTT;     



     for(;;) {



	 



	 if (do_send){



	    // get the next packet



	    // this method will block untl somethin can be read



	    next_p = packet_queue.get_next_packet();



	    frame.set_type(DATA_FRAME); // mark frame as data frame



	    frame.set_seq(next_seq_no); // set seq_no for packet



	    frame.set_packet(next_p);



	    send_to_physical(frame);



	 }



	 // Read ACK from physical layer, but this function



	 // will block for up to wait_time milliseconds



	 result = read_from_physical(read_frame, wait_time);



	 if (read_frame.get_type() != ACK_FRAME){



	    // something is very wrong since receiver is trying



	    // to piggyback ACK with Data, which is not supported



	    // in this algoritm



	    exit(1); // panic!!!



	 }



	 if (result == TIME_OUT){



	    // Timeout occurred, so send the same frame again



	    do_send = true;



	    continue; // try to send again



	 }



	 else if (read_frame.get_seq() == next_frame.get_seq()){



	    // ACK for current frame has arrive



	    // Move to send next frame on the queue



	    packet_queue.dequeue();  



	    // change seqence number



	    next_seq_no = (next_seq_no + 1) % 2;



	    do_send = true;



	 }



	 else {



	      // If we here , we are in trouble



	      // We got a repeated ACK, meaning that 



	      // receiver is out sync because our Timeout is too



	      // short.



	      // Discard this ACK, and wait for ACK for this Frame



	      do_sent = false;



	      continue;



	 }



     }



     	     



}