Test Papers / Previous Question Papers of IGNOU CS09 Data Communications and Networking December 1997

ADCA / MCA (II Yr)
Term-End Examination

December, 1997

CS09 : Data Communications and Networking

Time: 3 hours
Maximum Marks: 75

1 (a) Select the correct answer from the following: [8]

(i) Which two of these network standards are well suited to delivering time critical data?
· X.25
· IEEE 802.5
· Frame Relay
· ATM

(ii) Which of the following is one advantage that FDDI has over Token ring?
· Fibre optic cable is difficult to wiretap
· FDDI is capable of isolating cable breaks
· FDDI provides fair and timely access to networks
· FDDI has built in ring management

(iii) TCP uses the _________ mechanism to decide how much information a node can send or receive.

(iv) The most common type of data seen on a Netware LAN is ___________.

(v) OSI directory services are derived from
· CCITT X.400
· IEEE X.400
· CCITT X.500
· IEEE X.500

(vi) Gateways can function all the way upto
· Transport layer
· Session layer
· Presentation layer
· Application layer

(vii) Which is not an advantage of contention?
· Low overhead
· High user throughput at low traffic levels
· Simple access methods
· Probabilistic

(viii) Ethernet LAN uses
· Polar encoding
· Differential Manchester encoding
· Manchester encoding
· NRZ

(b) What signal-to-noise ratio is needed to put a T1 carrier on a 50 KHz line? [4]

(c) Frames of 1000 bits are sent over a 1 Mbps satellite channel. Acknowledgements are always piggybacked into data frames. The heads are very short. Three bit sequence numbers are used. What is the maximum achievable channel utilization for a protocol using goback n? [6]

(d) Consider the following network.

Draw the internal route tables for the following virtual circuits in the given order:
ABDE
ACD
BCDE
DEDE
DCBA [7]

(e) For hierarchical routing with 4800 IMPs what region and cluster sizes should be chosen to minimize the size of the routing table for 3-layer hierarchy? [5]

2 (a) What are the advantages of digitized transmission over the analog one? [5]

(b) A good number of voice signals are transmitted as digital bit streams over a digital channel. Explain a suitable scheme for transmission. [8]

(c) What is the advantage of frequency modulation over amplitude modulation and at what cost? [3]

3 (a) What is CRC error detection scheme? Explain how such a scheme is most efficient for the detection of burst errors? [8]

(b) A 3000 long T1 trunk is used to transmit 64 byte frames using Goback N Protocol. If the propagation speed is 6 m sec / km ,how many bits should the sequence number be? [7]

4 (a) Comment on packet fragmentation in Internetworking? [6]

(b) Explain Irland’s heuristics in the context of packet discarding. [6]

(c) “Centralized routing is always better as compared to the isolated routing.” Comment. [3]

5 (a) Explain IEEE, 802.3 MAC sublayer frame format. What is binary exponential back off algorithm? [10]

(b) Explain the possible problems which a 802.3 – 802.5 bridge should solve. [5]

6 (a) Explain [5]
(i) Indirect static and forward lockup deadlock.
(ii) Reassembly lockup.

(b) Suggest technique for avoiding indirect store and forward deadlock. [4]

(c)Where are the following operations carried out in electronic mail system? [6]
(i) Undelete previously deleted message.
(ii) Move message to another mail Box.
(iii) Deferred delivery of the mail.