void generate_next_arrival()
{
double x,log(),ceil();
struct event *evptr;
if (TRACE>2)
printf(" GENERATE NEXT ARRIVAL: creating new arrival\n");
x = lambda*jimsrand()*2; /* x is uniform on [0,2*lambda] */
/* having mean of lambda */
evptr = (struct event *)malloc(sizeof(struct event));
evptr->evtime = time + x;
evptr->evtype = FROM_LAYER5;
if (BIDIRECTIONAL && (jimsrand()>0.5) )
evptr->eventity = B;
else
evptr->eventity = A;
insertevent(evptr);
}
int init(void) /* initialize the simulator */
{
int i;
float sum, avg;
float jimsrand();
printf("----- Stop and Wait Network Simulator Version 1.1 -------- \n\n");
printf("Enter the number of messages to simulate: ");
scanf_s("%d",&nsimmax);
printf("Enter packet loss probability [enter 0.0 for no loss]:");
scanf_s("%f",&lossprob);
printf("Enter packet corruption probability [0.0 for no corruption]:");
scanf_s("%f",&corruptprob);
printf("Enter average time between messages from sender's layer5 [ > 0.0]:");
scanf_s("%f",&lambda);
printf("Enter TRACE:");
scanf_s("%d",&TRACE);
srand(9999); /* init random number generator */
sum = 0.0; /* test random number generator for students */
for (i=0; i<1000; i++)
sum=sum+jimsrand(); /* jimsrand() should be uniform in [0,1] */
avg = (float)(sum/1000.0);
if (avg < 0.25 || avg > 0.75) {
printf("It is likely that random number generation on your machine\n" );
printf("is different from what this emulator expects. Please take\n");
printf("a look at the routine jimsrand() in the emulator code. Sorry. \n");
return -9;
}
ntolayer3 = 0;
nlost = 0;
ncorrupt = 0;
time=0.0; /* initialize time to 0.0 */
generate_next_arrival(); /* initialize event list */
return 0;
}
/************************** TOLAYER3 ***************/
void tolayer3(int AorB,struct pkt packet)
{
struct pkt *mypktptr;
struct event *evptr,*q;
////char *malloc();
float lastime, x, jimsrand();
int i;
ntolayer3++;
/* simulate losses: */
if (jimsrand() < lossprob) {
nlost++;
if (TRACE>0)
printf(" TOLAYER3: packet being lost\n");
return;
}
/* make a copy of the packet student just gave me since he/she may decide */
/* to do something with the packet after we return back to him/her */
mypktptr = (struct pkt *)malloc(sizeof(struct pkt));
mypktptr->seqnum = packet.seqnum;
mypktptr->acknum = packet.acknum;
mypktptr->checksum = packet.checksum;
for (i=0; i<20; i++)
mypktptr->payload[i] = packet.payload[i];
if (TRACE>2) {
printf(" TOLAYER3: seq: %d, ack %d, check: %d ", mypktptr->seqnum,
mypktptr->acknum, mypktptr->checksum);
for (i=0; i<20; i++)
printf("%c",mypktptr->payload[i]);
printf("\n");
}
/* create future event for arrival of packet at the other side */
evptr = (struct event *)malloc(sizeof(struct event));
evptr->evtype = FROM_LAYER3; /* packet will pop out from layer3 */
evptr->eventity = (AorB+1) % 2; /* event occurs at other entity */
evptr->pktptr = mypktptr; /* save ptr to my copy of packet */
/* finally, compute the arrival time of packet at the other end.
medium can not reorder, so make sure packet arrives between 1 and 10
time units after the latest arrival time of packets
currently in the medium on their way to the destination */
lastime = time_local;
/* for (q=evlist; q!=NULL && q->next!=NULL; q = q->next) */
for (q=evlist; q!=NULL ; q = q->next)
if ( (q->evtype==FROM_LAYER3 && q->eventity==evptr->eventity) )
lastime = q->evtime;
evptr->evtime = lastime + 1 + 9*jimsrand();
/* simulate corruption: */
if (jimsrand() < corruptprob) {
ncorrupt++;
if ( (x = jimsrand()) < .75)
mypktptr->payload[0]='Z'; /* corrupt payload */
else if (x < .875)
mypktptr->seqnum = 999999;
else
mypktptr->acknum = 999999;
if (TRACE>0)
printf(" TOLAYER3: packet being corrupted\n");
}
if (TRACE>2)
printf(" TOLAYER3: scheduling arrival on other side\n");
insertevent(evptr);
}
