Assignment3: Transport Layer -> Reliable Data Transfer
CS390 Data Networking
YOU MAY WORK WITH A PARTNER // GO-BACK-N IS EXTRA CREDIT
In this assignment you and your partner will explore the stop and wait, selective repeat
reliable, and go-back-n (extra credit) data transfer protocols. For each protocol create a sender
which breaks up a 10M file into 1K segments and sends the segments to the receiver. Each
time a segment is sent the probability that a segment will:
-
arrive okay 70%
not arrive (use a timeout) 10%
be corrupted (use a random bit error) 10%
arrive out of order (use a sequence number) 10%
at the receiver.
After the receiver has received to segment the receiver will send a response (ack/nack ).
Each time the ack/nack is sent to probability that the ack/nack will:
-
arrive okay 70%
not arrive (use a timeout) 10%
be corrupted ( use a random bit error) 10%
arrive out of order (use a sequence number) 10%
For each protocol, write a sender and receiver that handles reliable data transfer. If you are
working with a partner, you and your partner should divide the work up so that one partner
writes the sender and the other partner writes the receiver.
You should try to realistically simulate unreliable data transfer:
- to simulate a segment that does not arrive at the receiver:
For the stop and wait protocol you should not send the segment to the receiver and
have the absence of an ack from the receiver trigger a timeout. Follow this link to see
how to test for a timeout on a receive:
http://stackoverflow.com/questions/30395258/setting-timeout-to-recv-function
For sliding window protocols it is more challenging because you need to be able to have
multiple in flight segments… and if each segment send is followed by a recv for the ack,
you won’t be able to the send the next segment after the lost segment until the recv for
the lost segment’s ack times out... unless you use threads (a different course) so this
reduces to stop and wait… not good.
So for the sliding window protocols send a segment to the receiver with a flag that
marks the segment as “YOU AREN’T SUPPOSED TO GET THIS”, then have the receiver
send back an ack that says to the sender “I DIDN’T GET THE SEGMENT”. Deal with the
simulated timeout after the rest of the segments in the window have been sent.
-
to simulate a corrupted segment you should generate a random bit error in the
segment and have the receiver detect the bit error through a checksum.
-
to simulate a segment which arrives out of order you should include a sequence
number in each segment and transmit a segment with the wrong sequence number two
receiver.
Provide feedback in your program for the protocol. For no error, have the sender/receiver
print out the action that was taken when a segment/ack is send/received. Have the
sender/receiver print out the TYPE of unreliable data transfer detected, then print out the
action taken to deal with the unreliable data transfer. For example (stop and wait):
Receiver:
Receiver:
Receiver:
resending
segment corrupted, bad checksum, sending nack
segment 42 received, sending ack42
segment 42 received, duplicate segment, ignoring,
ack42