June 1998

Question Paper of CS-09 – Data Communication & Network of June 1998 from IGNOU

1 (a)(i)Which of the following access control methods is probabilistic?
Token passing.
Sliding window
(ii) Which three of the following terms are related?
Connection ID.
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
IEEE 802.6

(v) Which of the two networks can use possible hubs?
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

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

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

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

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

(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?

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

(b) Why is PCM sampling time set at 125 msec?
3 (a) What are the limiting factors on transmission capacity of physical mediums?

(b) Discuss the channel capacity in the presence of noise (refer to Shannon�s Law for explanation).

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

4 (a) Describe the relative advantages and disadvantages of
(i) Terrestrial links
(ii) Satellite links
(iii) Radio links
(iv) Optical fiber transmission
(b) Discuss line utilization in Stop and Wait type of protocol.
5 (a) Draw the control field of X.25 supervisory frame and explain it.
(b) What is binary exponential back-off algorithm in IEEE 802.3 protocol and why is it used?
(c) What is the acknowledgement procedure in IEEE 802.5 protocol?

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

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