June 2002

Question Paper of CS-09 – Data Communication & Network of June 2002 from IGNOU

1 (i) A digital signalling system is required to operate at 9600 bps. If a signal element en codes 16 bit word, what is the minimum bandwidth required for this channel?

(ii) Describe the various issues related to measuring network performances.

(iii) Using Dijkstra�s routing algorithm, find out a least cost route to all other nodes for nodes 1 through 6 for the following network.

Do the same for Bellman-Ford algorithm.

(iv) PPP (Point to Point Protocol) is based closely on HDLC which uses bit stuffing to prevent accidental flag bytes within the payloads from causing confusion. Suggest atleast one reason why PPP uses character stuffing instead.

(v) With reference to transport layer, outline the operation of 3-way handshaking. How does the 3-way handshake prevent old duplicate connection initiation from causing confusion? Show it diagrammatically.

2 Discuss the differences between the following:
� Circuit switched network and Packet switched network
� Pulse code modulation and Delta modulation
� 1-persistent CSMA nad Non-persistent CSMA
� Choke packets and Weighted fair queuing
� AAL1 and AAL2 protocols

3 (i) Draw the waveform for 11001110 in each of the following encoding methods :
� RZ
� Manchester
� Different Manchester

(ii) Where is the multicasting routing used? Discuss its adventages and disadvantages.

(iii) Why is there a need for compression? Compare between JPEG and MPEG standards.

4 (i) What is the advatage of QAM over ASK or PSK? Draw an 8-QAM constellation diagram with 2 amplitude and four phases.

(ii) Describe five types of cabling used in 802.3 LANS.

(iii) Give a potential diasadvantages when Nagle�s algorithm is used on a badly congested network.

5 (i) Discuss the following in the context of IEEE 802.3 frame format. List the important features of addressing. What is the need of minimum length frame?

(ii) Describe in detail about the physical description, applications of the following :
� Fibre optics
� Microwave
� Broadcast Radio

6 (i) Compare the individual fields of IPv4 header with IPv6 header. Account for the functionality provided by each IPv4 field by showing how the same functionality is provided in IPv6.

(ii) Discuss the advantages and disadvantages of credits vs. sliding window protocol.

(iii) Provide a brief explanation for each of the following equations :
(a) Under a light load, which LAN has smaller delay : Ethernet or Token ring.
(b) Under a high load, which LAN has a smaller delay : Ethernet o Token ring?

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