Department of Electrical and Computer Engineering
Concordia University
Communications Networks and Protocols - COEN 366
Inst.: Ferhat Khendek
Winter 2026
Assignment #1 (Due for Friday February 06, 2026, 23:59)
Question 1.
a. List 2 distributed application protocols that rely on TCP, 1 application protocol that
relies on UDP, and explain how they are used.
b. Explain briefly and clearly the role of each of the following layers:
Link, Transport, and Presentation.
Question 2. Control flow function is performed at layer 2 and layer 4 of the OSI
architecture. Is this redundant or necessary? Explain.
Question 3.
Consider a code of 10-bits long words (from 0000000000 to 1111111111). Now, you add
4 parity bits, p1, p2, p3 and p4 for each word, with:
p1 = b9 Å b8 Å b7 Å b6 Å b5
p2 = b4 Å b3 Å b2 Å b1 Å b0
p3 = p1 Å p2
p4 = p3
What is the Hamming distance of this new code? Explain in a rigorous manner.
Question 4.
A CRC error detection system has a pattern P = 1011. Determine the FCS it would
generate for message M = 10010010 and give the transmitted frame T.
Question 5.
In Go-Back-N scheme, REJ(N) and RR(N) frames are used by HDLC both to acknowledge
correct receipt of frames up to N-1. What is the difference between these two control
frames?
Question 6.
Two nodes (A and B) use sliding-window protocol with a 3-bit sequence number. The
ARQ mechanism, Go-Back-N is used with a window size of 5. Assuming A is transmitting
and B is receiving, show the window positions for the following succession of events.
a. Before A sends any frame.
b. After A sends frames 0, 1, 2, 3 and B acknowledges 0, 2 and the ACK are received by
A.
c. After A sends frames 4, 5, 6, 7 and B acknowledges 6 and the ACK is received by A.
d. After A sends frames 0, 1 and B acknowledges 1 and the ACK is received by A.
1
Question 7. Find the errors in the following HDLC operations.
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+ + !I
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+ J + !.
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/ DA M !
C"
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+ + !.
!
2
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