Dec 1997

Question Paper of CS-09 – Data Communication & Network of Dec 1997 from IGNOU

1 (a) Select the correct answer from the following:

(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?
(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?

(d) Consider the following network.

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

(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?

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

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

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

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

(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?

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

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