Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: THEend8_
COMP3234 Computer and Communication Networks
Problem Set Assignment Two
Total 6 points
Answer all questions. Hand-in the assignment via the Moodle System.
Question 1 (1.2 points) (This question is related to ILO2a – “be able to comprehend the challenges and explain
the principles in providing reliable communication in an unreliable medium”, and ILO3 – “be able to calculate
packet delay, throughput, and channel efficiency according to different network protocols”.)
The Trivial File Transfer Protocol (TFTP) is an application layer protocol that uses the Stop-and-
Wait ARQ and runs on top of UDP to support reliable data transfer. To transfer a file from a
server to a client, the server breaks the file into blocks of 1024 bytes and sends these blocks to
the client using Stop-and-Wait ARQ.
Consider transferring a 2 MiB file from a server to a client using TFTP over a 1 Gb/s network
with a propagation delay of 3 milliseconds between the two ends. Suppose that each TFTP data
packet consists of a 1024-byte file block and 46 bytes of headers (from various layers including
TFTP header), and each TFTP acknowledgment packet consists of 46 bytes of headers only.
a) (0.6) Assume the transmissions are error-free (no corruption & loss), find the total time
used by the system to reliably transfer that 2 MiB file and the application file transfer
throughput. (As the size of the TFTP acknowledgment packet is given, please include it in
the analysis.)
b) (0.6) Assume TFTP adopts a fixed retransmission timeout duration of 1 second and the
underlying network is moderately congested with a loss rate of 1/64, estimate the total
time used by the system to reliable transfer that 2 MiB file and the average throughput of
the transfer.
Ignore queuing delay and processing delay.
Question 2 (1 point) (This question is related to ILO2a – “be able to comprehend the challenges and explain
the principles in providing reliable communication in an unreliable medium”, and ILO3 – “be able to calculate
packet delay, throughput, and channel efficiency according to different network protocols”.)
Consider the GBN and SR protocols. Suppose you are designing a sliding window protocol for a
30 Mbps point-to-point satellite link with a propagation delay of 420 milliseconds (between the
two ends). Assume that the size of each segment is 1500 bytes (including the data payload and
headers). To achieve the best throughput, what is the minimum number of bits in the header
for storing the sequence number in the following cases?
a) (0.5) Go-Back-N
b) (0.5) Selective Repeat