Wolph

/* Protocol 4 (sliding window) is bidirectional and is more robust than * protocol 3. * * To compile: cc -o protocol4 p4.c simulator.o * To run: protocol4 events timeout  pct_loss  pct_cksum  debug_flags * * Written by Andrew S. Tanenbaum * Revised by Shivakant Mishra */#define MAX_SEQ 1typedef enum {frame_arrival, cksum_err, timeout} event_type;#include <stdio.h>#include <stdlib.h>#include "protocol.h"void protocol4 (void){  seq_nr next_frame_to_send;	/* 0 or 1 only */  seq_nr frame_expected;	/* 0 or 1 only */  frame r, s;	/* scratch variables */  packet buffer;	/* current packet being sent */  event_type event;  int last_ack;/* put protocol number and process id in log */  sprintf(logbuf,"XXX4 protocol4, pid=%d\n", getpid());  flog_string(logbuf);  next_frame_to_send = 0;	/* next frame on the outbound stream */  frame_expected = 0;	/* number of frame arriving frame expected */  from_network_layer(&buffer);	/* fetch a packet from the network layer */  init_frame(&s);  s.kind = data;  s.info = buffer;	/* prepare to send the initial frame */  s.seq = next_frame_to_send;	/* insert sequence number into frame */  s.ack = 1 - frame_expected;	/* piggybacked ack */  srand(time(0));  //usleep(rand() % 10000);  //to_physical_layer(&s);	/* transmit the frame */  start_timer(s.seq);	/* start the timer running */  while (true) {        wait_for_event(&event);	/* could be: frame_arrival, cksum_err, timeout */        if ((event != frame_arrival) && (event != cksum_err) &&            (event != timeout)) printf("\n SOMETHING WEIRD\n");        if (event == frame_arrival) { /* a frame has arrived undamaged. */                from_physical_layer(&r);	/* go get it */                if (r.seq == frame_expected) {                        /* Handle inbound frame stream. */                        to_network_layer(&r.info);	/* pass packet to network layer */                        inc(frame_expected);	/* invert sequence number expected next */                }                if (r.ack == next_frame_to_send) { /* handle outbound frame stream. */                        stop_timer(r.ack); /*JH*/ /* necessary to prevent superfluous timeouts */                        from_network_layer(&buffer);	/* fetch new packet from network layer */                        inc(next_frame_to_send);	/* invert sender's sequence number */                        init_frame(&s);                        s.kind = data;                        s.info = buffer;	/* construct outbound frame */                        s.seq = next_frame_to_send;	/* insert sequence number into it */                        s.ack = 1 - frame_expected;	/* seq number of last received frame */                        to_physical_layer(&s);	/* transmit a frame */                }        }        if(event == timeout){            init_frame(&s);            s.kind = data;            s.info = buffer;	/* construct outbound frame */            s.seq = next_frame_to_send;	/* insert sequence number into it */            s.ack = 1 - frame_expected;	/* seq number of last received frame */            to_physical_layer(&s);	/* transmit a frame */            start_timer(s.seq);	/* start the timer running */        }  }}main (int argc, char *argv[]){  int timeout_interval, pkt_loss, garbled, debug_flags;  long event;  if (!parse_first_five_parameters(argc, argv, &event, &timeout_interval,                                   &pkt_loss, &garbled, &debug_flags))  {    printf ("Usage: p4 events timeout loss cksum debug\n");    exit(1);  }  printf("\n\n Simulating Protocol 4\n");  start_simulator(protocol4, protocol4, event, timeout_interval, pkt_loss, garbled, debug_flags);}