Code: C-12 / T-10 Subject: DATA COMMUNICATION & NETWORKS
Time: 3 Hours Max. Marks: 100
NOTE: There are 11 Questions in all.
· Question 1 is compulsory and carries 16 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.
· Answer any THREE Questions each from Part I and Part II. Each of these questions carries 14 marks.
· Any required data not explicitly given, may be suitably assumed and stated.
Q.1 Choose the correct or best alternative in the following: (2x8)
a. Propagation time is _____________ proportional to distance and __________ proportional to propagation speed.
(A) Inversely, Directly (B) Directly, Inversely
(C) Inversely, Inversely (D) Directly, Directly
b. Coding can help in _________ at the receiver.
(A) Synchronization (B) Error Detection
(C) Attenuation (D) Both (A) and (B)
c. A 56 K modem can download at a rate of __________ Kbps and upload at a rate of ________ Kbps.
(A) 33.6; 33.6 (B) 33.6; 56.6
(C) 56.6; 33.6 (D) 56.6; 56.6
d. Error detection at data link level is achieved by
(A) Bit Stuffing. (B) CRC.
(C) Hamming Code. (D) Equalizations.
e. DMT is a modulation technique that combines elements of ________ and _________.
(A) FDM; TDM (B) QDM; QAM
(C) FDM; QAM (D) PSK; FSK
f. What is present in all HDLC field formats?
(A) P/F bit (B) N (R)
(C) N (S) (D) Code bits
g. A Bluetooth frame needs __________ 
for hopping and
control mechanisms.
(A) 625 (B) 259
(C) 3 (D) A multiple of 259
h. Decryption and Encryption of data are the responsibility of________layer.
(A) Presentation (B) Data Link
(C) Sessions (D) Network.
PART I
Answer any THREE Questions. Each question carries 14 marks.
Q.2 a. Complete the following table : (8)
|
Sno. |
Characteristics |
10 Base 2 |
10 Base 5 |
10 Base T |
|
1 |
No of Segments |
|
|
|
|
2 |
Segment Length |
|
|
|
|
3 |
Number of Stations/Segment |
|
|
|
|
4 |
Topology |
|
|
|
b. What do you mean by Star LAN? What is the speed and segment length of Star LAN? Explain transceiver of a Star LAN. (6)
Q.3 a. (i) Can a device have more than one IP address. Give reason
(ii) Why would an application use UDP instead of TCP?
(iii) How can TCP handle urgent data?
(iv) What is MTU and how fragment is related to it? (8)
b. Draw the IP datagram header format. “IP datagram has a checksum field
still its called unreliable protocol.” Justify. (6)
Q.4 a. We have four sources, each creating 250 characters per sec. If the interleaved unit is a character and 1 synchronizing bit is added to each frame. Find
(i) the data rate of each source,
(ii) the duration of each character in each source,
(iii) the frame rate,
(iv) the duration of each frame (8)
b. Discuss two-dimensional parity check method. Discuss the strength & weakness of the method in error detection. (6)
Q.5 a. Explain the principle of :
(i) Message Switching (ii) Circuit Switching
(iii) Packet Switching. (6)
b. Deduce the formula to find, in a three-stage crossbar switch, the number of cross-points ‘n’ in terms of the number of input/output lines ‘N’, the number of first – and third – stage switches ‘K’, and the number of second –stage switches ‘L’? (5)
c. Explain TDM. (3)
Q.6 a. Give the Electrical & Functional specifications of RS-232C standard. (6)
b. What do you mean by Link-to-Link layers of OSI reference model?
Explain functions of each layer briefly. (8)
PART II
Answer any THREE Questions. Each question carries 14 marks.
Q.7 a. What is an internetwork? State and compare internetworking devices used to connect different LAN segments. (6)
b. What is the function of Modem? Define the bandwidth of Line. What is the bandwidth of a traditional telephone line? (4)
c. List the operational features of ASK and QAM. (4)
Q.8 a. Justify the statement “Slotted ALOHA achieves double efficiency than pure ALOHA”. (8)
b. (i) What is the difference between a confirmed service and an unconfirmed service? Give examples for each.
(ii) Define 1-persistent and p-persistent CSMA. (6)
Q.9 a. Compare flow control and congestion control. Why a choke packet is used? (4)
b. Compare and contrast Link state and distance vector routing algorithms? (4)
c. Using Dijkstra’s algorithm, compute the shortest path
from E to all other network nodes. (6)
Q.10 a. What is the mechanism of
(i) Stop-and-wait and
(ii) Continuous ARQ strategies. (6)
b. (i) Describe the term “reciprocity” in relation to RSA algorithm.
(ii) Encrypt the following message using monoalpha betic substitution
with key = 4 :-
THIS IS A GOOD EXAMPLE (4)
c. Explain the working principle of E-mail. Compare the mailing protocols – SMTP and MIME. (4)
Q.11 a. Explain any THREE of the following:
(i) IEEE 802.6.
(ii) FDDI.
(iii) Transmission Media.
(iv) Encryption and Decryption techniques.
(v) ISDN. (9)
b. Discuss the following :-
(i) ATM cells.
(ii) ATM signalling. (5)