1. Match the following:
(a) Physical layer (i) Allow resources to network access
(b) Data link layer (ii) Move packets from one destination to another
(c) Network layer (iii) Process to process message delivery
(d) Transport layer (iv) Transmission of bit stream
(e) Application layer (v) Formation of frames

Codes: a b c d e
(A) iv v ii iii i
(B) v iv i ii iii
(C) i iii ii v iv
(D) i ii iv iii v

June 2014 – Paper II Q.No 5
Ans:- A
Explanation:- If you find many options confusing choose one which you are very confident and about and then compare the rest of the options. Here, Transmission of bit streams is the work of the physical layer is something which one can be very sure about. So, a is matched to iv. There is only one option which does that and it is A. So just compare the rest of the codes and confirm that they are right. Data link layer is formation of frames. Network layer move packets from one destination to another. Transport layer is process to process message delivery and finally Application layer is allow resources to network access. So the correct answer is A.

2. Which layers of the OSI reference model are host-to-host layers?
(A) Transport, session, presentation, application
(B) Network, transport, session, presentation
(C) Data link, network, transport, session
(D) Physical, data link, network, transport
June 2014-Paper III
Ans:- A
Explanation:- The host-to-host layers are the four from the upper layers. Application, presentation, session, transport. The last three are referred to as media layers.

3. Encryption and decryption is the responsibility of _____layer.
(A) Physical
(B) Network
(C) Application
(D) Data link
December 2013 – Paper II
Ans:- C
Explanation:- Since the presentation layer is not available as an option, the right answer is Application. In the explanation above for Presentation layer, there is a mention that in practice it is combined with Application. So the right answer is C.

4. Which layer of OSI reference model is responsible for decomposition of messages and generation of sequence numbers to ensure correct re-composition from end to end of the network?
(A) Physical
(B) Data link
(C) Transport
(D) Application
December 2013 – Paper III
Explanation:- Actually physical, data link and application are completely ruled out for the above question and so the right answer is C.