Previous Year Questions: OSI Layer | Computer Networks - Computer Science Engineering (CSE) PDF Download

Q1: In the following pairs of OSI protocol layer/sub-layer and its functionality, the INCORRECT pair is  (2014 SET 3) 
(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
Ans: (b)
Sol: 
A. One of the main functionality of Network Layer is Routing. So, option (A) is CORRECT.
B. Bit Synchronization is always handled by Physical Layer of OSI model but not Data Link Layer. So, option (B) is INCORRECT.
C. End – to – End Process Communication is handled by Transport Layer. So, option (C) is CORRECT.
D. MAC sub layer have  types of protocols (Random, Controlled and Channelized Access).
So, option (B) is incorrect pair.

Q2: An IP machine Q has a path to another IP machine H via three IP routers R1, R2, and R3.  (2014 SET 2) 
Q---R1---R2---R3---H
H acts as an HTTP server, and Q connects to H via HTTP and downloads a file. Session layer encryption is used, with DES as the shared key encryption protocol. 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
Ans: (c) 
Sol: [I1] intruder cant see URL because it is well encrypted by DES at session layer..
[I2] TCP PORT number available to intruder because TCP header contains source as well as destination address.
[I3] Network layer header contains Source as Well as Destination IP.
[I4] Link address unavailable because on sniffing at R2 intruder can see link address of R1, R3 ,only not link address of  Q and  H
Answer is C.