Test Papers / Previous Question Papers of IGNOU CS09 Data Communications and Networking June 1998

ADCA / MCA (II Yr)
Term-End Examination

June, 1998

CS09 : Data Communications and Networking

Time: 3 hours
Maximum Marks: 75

1 (a)(i)Which of the following access control methods is probabilistic? [8]
· Polling.
· Contention.
· Token passing.
· Sliding window

(ii) Which three of the following terms are related?
· Port.
· Connection ID.
· Socket.
· Service Address.

(iii) Which two of the following statements are true?
· The data link layer deals with device to device traffic.
· The network layer deals with traffic between upper layer processes.
· The transport layer deals with traffic between end nodes
· All of the above are true.

(iv) Which two of the following are regarded as WAN Protocols?
· Frame Relay
· Slip
· IEEE 802.6
· X.25

(v) Which of the two networks can use possible hubs?
· Ethernet
· Arcnet
· Token Ring
· All of the above

(vi) What are the primary characteristics that distinguish a cell from a packet?
· Cells are generally smaller than packets.
· Cells do not incorporate physical address.
· All cells have the same fixed length.
· Packets cannot be switched.

(vii) Which two of these standards use token passing for media access control?
· IEEE 802.4
· IEEE 802.6
· Frame Relay
· FDDI

(viii) Which two of these standards are designed to support audio data?
· IEEE 802.3
· ATM
· ISDN
· Frame Relay

(b)Television Channels are 6 MHz wide. How many bits/sec can be sent if 4-level digital signals are used? [6]

(c) Compare the maximum data rate of noiseless 4 KHz channel using

(i) Analog encoding with 2 bits per sample. [5]
(ii) The T1 PCM system. [6]

(d) Class 0 of the OSI transport protocol does not have any explicit flow control procedure. Does this mean that a fast sender can overload slow transmitter with data? [5]

2 (a) How does digital transmission work? How does delta modulation improve the performance of PCM (Pulse Code Modulation). [10]

(b) Why is PCM sampling time set at 125 msec? [5]

3 (a) What are the limiting factors on transmission capacity of physical mediums? [5]

(b) Discuss the channel capacity in the presence of noise (refer to Shannon’s Law for explanation). [5]

(c)Assume a bandwidth of 3100 Hz. A typical value of S/N for a voice grade line is 30 dB. Calculate channel capacity. [5]

4 (a) Describe the relative advantages and disadvantages of
(i) Terrestrial links
(ii) Satellite links
(iii) Radio links
(iv) Optical fiber transmission [10]
(b) Discuss line utilization in Stop and Wait type of protocol. [5]

5 (a) Draw the control field of X.25 supervisory frame and explain it. [5]
(b) What is binary exponential back-off algorithm in IEEE 802.3 protocol and why is it used? [5]
(c) What is the acknowledgement procedure in IEEE 802.5 protocol? [5]

6 (a) Explain briefly how flow control and buffer management is done in transport layer. [5]
(b) Draw all synchronization points in session layer. [5]