Gujarat University
MCA Semester IV
Networking Technologies IV
Date: 2nd August, 1991 Marks:50
Instructions:
1. Answers to the two sections must be written in separate answer-books.
2. Figures to the right indicate full marks allocated to question.
3. Assure suitable data wherever necessary.
Section I
Q-1 Draw the ISO reference model for computer networks and describe the various levels of abscration.
Explain the working of the physical layer. [9]
OR
Q-1 (a) State the relative merits and demerits of the star connection over the Ring connection in computer
networks. [9]
(b) What are the three fundamental types of modulation methods used in analog as well as digital
communication? Give two relative advantages and disadvantages of each of the three types of
modulation.
(c) The 10 Hz sine wave is modulated by a square wave, which varies from 0 to full-scale every 0.5
seconds. Sketch the time domain representation for the following three cases:
(i) AM
(ii) FM with frequency shift from 10 Hz to 20 Hz
(iii) PM with a phase shift of 1800.
Q-2 Answer any three of the following: [8]
(a) Compare RS-232, RS-422, RS-423 and RS-485 with respect to bit rate, distance single ended VS.
differential signals and signal voltage levels.
(b) What are the functions of MODEM?
(c) State the Generator Polynomial commonly used in SDLC protocols.
Draw the circuit consisting of a shift Registers and Ex-OR gates to generate the CRC check sum for this polynomial.
(d) Explain aliasing error and jitter.
Q-3 State the Nyquist Sampling Theorem. How does the Nyquist rate help determine the no. of users a TDM
system can support? A system must be designed to support 18 users. Each user signal has a bandwidth of 3
KHz. The Nyquist sampling in this application, needs 50% over sampling. How many samples per second
must the system provide?
OR
Q-3 (a) What is Channel capacity? How is it related to bandwidth? [8]
(b) State the Shannon’s formula relating a communication channel’s bandwidth and capacity.
What is the channel capacity for a signal power of 50 W, noise power of 3 W and bandwidth of 15 KHz?
(c) What is bandwidth reduction? How does it differ from bandwidth compression? Give an example of
each.
Section II
Q-4 (a) State the important properties of the following media for data communication: [9]
Fiber-optic cable, coaxial cable, flat cable, twisted-pair of wires.
(b) What are the two causes of Late Symbol Interference? How does looking at the eye pattern help the
channel designer?
(c) Explain the terms:
Equalization, Precompensation, Adaptive Equalizer, CMRR
Q-5 (a) A system is being designed to handle five pairs of users. Sketch the system, using block diagram, for
Implementation with: [8]
(i) SDM
(ii) FDM
(iii) TDM
If the user signals are essentially similar, sketch the time-domain representation for both the SDM and TDM cases.
(b) A TDM system uses an identifying code for each user of a five-user system. Each user is connected by
the time division multiplexer for 20 ms and the identifier takes 20 ms. Calculate the fastest rate at which
each user can have access to the link if all five users must be served.
OR
Q-5 (a) Explain clearly the difference between FORNAT and PROTOCOL. [8]
(b) Where is SDLC used? What are some of its key characteristics?
(c) A system is using an 8-bit asynchronous format to send a 50-character message. If one start and one
stop bit be used, how many bits will have to be sent for the message?
Q-6 (a) In data communication systems, what is the relationship between slew rate and maximum band value?
[8]
(b) Define the following:
Framing error, Overrun error, Parity error.
Give the cause(s) for each one of the above errors.
(c) Explain the following terms for RS-232 communication system:
RTS, CTS, DSR, Ring Detector.
(d)Why is the break function sometimes needed? How is break detected at the detector?
OR
Q-6 (a) Describe the operation of the following four protocol systems: [8]
Command/ Response, Interrupt-Driven, Token-Passing, CSMA/CD
(b) Draw the circuit using EX-OR gates to generate parity bits for a 4-bit data group.
