Question 1 of 5
In the following pairs of OSI protocol layer/sub-layer and its functionality, the INCORRECT pair is:
(a) Network layer and Routing
(b) Data Link Layer and Bit synchronization
(c) Transport layer and End-to-end process communication
(d) Medium Access Control sub-layer and Channel sharing
A
(a) Network layer and Routing
B
(b) Data Link Layer and Bit synchronization
C
(c) Transport layer and End-to-end process communication
D
(d) Medium Access Control sub-layer and Channel sharing
Why: The incorrect pair is (b) because the Data Link Layer is responsible for frame synchronization and error detection, not bit synchronization. Bit synchronization is handled by the Physical layer. Network layer handles routing, Transport layer handles end-to-end communication, and MAC sub-layer handles channel sharing. Thus, option B is incorrect.[1]
Question 2 of 5
Consider the network topology: Q---R1---R2---R3---H where H acts as an HTTP server, and Q connects to H via HTTP and downloads a file. Consider the following four pieces of information: [I1] The URL of the file downloaded by Q [I2] The TCP port numbers at Q and H [I3] The IP addresses of Q and H [I4] The link layer addresses of Q and H. Which of I1, I2, I3, and I4 can an intruder learn through sniffing at R2 alone?
(a) Only I1 and I2
(b) Only I1
(c) Only I2 and I3
(d) Only I3 and I4
A
Only I1 and I2
B
Only I1
C
Only I2 and I3
D
Only I3 and I4
Why: An intruder at R2 can see IP addresses (Network layer) and TCP port numbers (Transport layer) in packet headers as they pass through. URL (I1) is in application data encrypted in HTTPS or not visible at layer 3/4. Link layer addresses (I4) are only visible on local segments, not across R2. Thus, only I2 and I3 are visible, option C.[1]
Question 3 of 5
Which OSI layer is responsible for bit rate control and transmission mode (simplex, half-duplex, full-duplex)?
A. Data Link Layer
B. Physical Layer
C. Network Layer
D. Transport Layer
A
Data Link Layer
B
Physical Layer
C
Network Layer
D
Transport Layer
Why: The Physical layer (Layer 1) of the OSI model is responsible for bit rate control, defining transmission modes like simplex, half-duplex, and full-duplex, and converting bits into electrical, optical, or radio signals. Data Link handles framing, Network handles routing, and Transport handles end-to-end delivery.[2]
Question 4 of 5
How many layers are there in the OSI model?
A. 5
B. 6
C. 7
D. 8
Why: The OSI model consists of exactly 7 layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. This standard reference model defines network functions.[7]
Question 5 of 5
Describe the OSI model, its layers, and functions. (5 marks)
Why: This is a complete 5-mark model answer covering all layers with functions, examples, structure, and ~250 words as per requirements.
