Gujarat University
MCA Semester IV
Networking Technologies IV
Date: 22nd August, 1996 Marks:50
Instructions:
1. Answers to the two sections must be written in separate answer-books.
2. Q. Nos. 1 and 6 carry 9 marks each. Other questions carry 8 marks each.
3. Make necessary assumptions, wherever required, and state them clearly.
Section I
Q-1 (a) What is the Nyquist Rate? If a continuos signal is sampled at a rate lower than the Nyquist rate, what will
be the effects?
(b) A communication channel can send 1,000,000 bits/second reliably. It is to be used for sending voice
signals each of which is sampled at 8 khz. Each sample as digitized by using an 8-bits A/D converter. How
many users can be accommodated using TDM in the communication channel?
Q-2 (a) State the Shannon’s Theorem.
What should be the bandwidth of the channel for obtaining a channel capacity of 10,000 bits/sec. When the
signal power is 16 times the noise power?
(b) A 10 MHz signal is to travel on a pair of wires. If the velocity of propagation on the wires be 75% of the
speed of light, how far would the signal travel during 0.1 microseconds.
OR
Q-2 (a) A 10 Hz sine wave is used as the carrier with a square wave as the modulating signal. The square wave is
symmetrical and has a cycle time of 1 second. Sketch the time domain representation for the following
methods of modulation:
i) Amplitude Modulation
ii) Frequency Modulation with the frequency shifting from 10 Hz to 20Hz.
iii) Phase Modulation with a phase shift of 180 degrees.
(b) How does a PLL work? How does it perform the demodulation of FM signals?
Q-3 (a) What is Manchester Encoding? Compare the bandwidth it uses to that of the NRZ method of encoding.
What are the advantages of Manchester encoding?
(b) A system is sending out the following pattern:
0101 1110 1000
Draw the output for both the Manchester and the NRZ Encoding methods.
OR
Q-3 (a) A system is sending 1 ms bits at a rate of 500 bits/sec. It uses –10V to +10V signals. The time to slew from
negative to positive should be less than 10 percent of the bit time. What is the minimum acceptable slew
rate in Volts/ms?
(b) An asynchronous data communication system uses RS-232 operation with voltage levels of +12V and –
12V, with Even parity, with 1 start bit and with 1.5 stop bits. Its data rate is 1000 bits/sec. Sketch the line
output vs. time for transferring the following:
i) A using ASCII code
ii) 58 using ASCII code
iii) 58 in binary
What is the signal state of the data line when-
i) There is no data on the line?
ii) There is a BREAK?
Section II
Q-4 (a) State the important properties of the following media for communication:
Fiber-optic cable, coaxial cable, flat cable, twisted-pair of wires
(b) What are the two causes of Intersymbol Interference? How does looking at the eye-pattern help the
channel designer?
(c) Explain the following terms as used in Data Communication:
Adaptive Equalizer, Pre-compensator, Help-Duplex systems, Bandwidth Compression and Bandwidth
Reduction, CMRR
Q-5 (a) For an Asynchronous Data Communication System, give the cause(s) for each of the following types of
errors:
Framing error, Parity error, Overrun error.
(b) Explain the following terms for an RS-232 communication system:
RTS, CTS, DSR, BTR, Ring Detector
(c) Compare RS-422, RS-423 and RS-485 with RS-232.
OR
Q-5 (a) Define the role of each layer in the OSI model of data communication.
(b) Sketch the seven-layer OSI model, which allows a plant executive to communicate with both the office
staff (using Ethernet) and the production staff (using MAP).
Q-6 Write notes on ANY THREE of the following:
1. UART 8251
2. CRC Checksum method of error detection
3. MODEMS
4. Cellular Networks
5. ISDN
