void stuff(void){
packet p;
dequeuet(p.load);
enqueue(p);
counter++;
newcount++;
if(newcount==stops){
newcount=1;
ii++;
p.eop=1;
}else{
p.eop=0;
}
to_network_layer(p);
}
void receiver3(void)
{
seq_nr frame_expected;
frame r, s;
event_type event;
frame_expected = 0;
while (true) {
wait_for_event(&event); /* possibilities: frame_arrival, cksum_err */
if (event == frame_arrival) {
/* A valid frame has arrived. */
from_physical_layer(&r); /* go get the newly arrived frame */
if (r.seq == frame_expected) {
/* This is what we have been waiting for. */
to_network_layer(&r.info); /* pass the data to the network layer */
inc(frame_expected); /* next time expect the other sequence nr */
}
init_frame(&s);
s.ack = 1 - frame_expected; /* tell which frame is being acked */
to_physical_layer(&s); /* only the ack field is use */
}
}
}
void protocol6(void)
{
seq_nr ack_expected; /* lower edge of sender's window */
seq_nr next_frame_to_send; /* upper edge of sender's window + 1 */
seq_nr frame_expected; /* lower edge of receiver's window */
seq_nr too_far; /* upper edge of receiver's window + 1 */
int i; /* index into buffer pool */
frame r; /* scratch variable */
packet out_buf[NR_BUFS]; /* buffers for the outbound stream */
packet in_buf[NR_BUFS]; /* buffers for the inbound stream */
boolean arrived[NR_BUFS]; /* inbound bit map */
seq_nr nbuffered; /* how many output buffers currently used */
event_type event;
enable_network_layer(); /* initialize */
ack_expected = 0; /* next ack expected on the inbound stream */
next_frame_to_send = 0; /* number of next outgoing frame */
frame_expected = 0; /* frame number expected */
too_far = NR_BUFS; /* receiver's upper window + 1 */
nbuffered = 0; /* initially no packets are buffered */
for (i = 0; i < NR_BUFS; i++) arrived[i] = false;
while (true) {
wait_for_event(&event); /* five possibilities: see event_type above */
switch(event) {
case network_layer_ready: /* accept, save, and transmit a new frame */
nbuffered = nbuffered + 1; /* expand the window */
from_network_layer(&out_buf[next_frame_to_send % NR_BUFS]); /* fetch new packet */
send_frame(data, next_frame_to_send, frame_expected, out_buf); /* transmit the frame */
inc(next_frame_to_send); /* advance upper window edge */
break;
case frame_arrival: /* a data or control frame has arrived */
from_physical_layer(&r); /* fetch incoming frame from physical layer */
if (r.kind == data) {
/* An undamaged frame has arrived. */
if ((r.seq != frame_expected) && no_nak)
send_frame(nak, 0, frame_expected, out_buf); else start_ack_timer();
if (between(frame_expected, r.seq, too_far) && (arrived[r.seq%NR_BUFS] == false)) {
/* Frames may be accepted in any order. */
arrived[r.seq % NR_BUFS] = true; /* mark buffer as full */
in_buf[r.seq % NR_BUFS] = r.info; /* insert data into buffer */
while (arrived[frame_expected % NR_BUFS]) {
/* Pass frames and advance window. */
to_network_layer(&in_buf[frame_expected % NR_BUFS]);
no_nak = true;
arrived[frame_expected % NR_BUFS] = false;
inc(frame_expected); /* advance lower edge of receiver's window */
inc(too_far); /* advance upper edge of receiver's window */
start_ack_timer(); /* to see if (a separate ack is needed */
}
}
}
if((r.kind==nak) && between(ack_expected,(r.ack+1)%(MAX_SEQ+1),next_frame_to_send))
send_frame(data, (r.ack+1) % (MAX_SEQ + 1), frame_expected, out_buf);
while (between(ack_expected, r.ack, next_frame_to_send)) {
nbuffered = nbuffered - 1; /* handle piggybacked ack */
stop_timer(ack_expected % NR_BUFS); /* frame arrived intact */
inc(ack_expected); /* advance lower edge of sender's window */
}
break;
case cksum_err: if (no_nak) send_frame(nak, 0, frame_expected, out_buf); break; /* damaged frame */
case timeout: send_frame(data, get_timedout_seqnr(), frame_expected, out_buf); break; /* we timed out */
case ack_timeout: send_frame(ack,0,frame_expected, out_buf); /* ack timer expired; send ack */
}
if (nbuffered < NR_BUFS) enable_network_layer(); else disable_network_layer();
}
}
