Gujarat University
MCA Semester IV
Networking Technologies IV
Date: 4th August, 1993 Marks:50
Instructions:
1. Answers to the two sections must be written in separate answer-books.
2. Q. Nos. 1 and 4 carry 9 marks each. Other questions carry 8 marks each.
Section I
Q-1 (a) Explain why an analog signal would carry more information than a digital one in a fixed amount of time.
Why , then, are digital and binary signals used extensively?
(b) What is Channel Capacity? What are the factors, which affect the capacity of a data communication
Channel? What is the Channel capacity of a channel with a bandwidth of 100 KHz, signal power equal to
1000 W, and noise power of 50 W?
Q-2 (a) What are the three fundamental types of modulation? What is varied in each case by the modulating
signals? Give two advantages and disadvantages of each of the three types of modulation.
(b) The 10-Hz sine wave is modulated by a square wave, which varies from 0 to full scale every 0.5 secs.
Sketch the time domain representation for these cases:
(i) AM . Assume any suitable value of depth of modulation.
(ii) FM. With the frequency shifting from 10 to 20 Hz, as the modulating square varies from 0 to full scale.
(iii) PM, with a phase shift of 180 degrees, as the modulating square wave varies from 0 to full scale.
OR
Q-2 (a) What are the two causes of intersymbol interference? How does looking at the eye pattern help?
(b) Explain the difference between FORMAT and PROTOCOL.
(c) Discuss SDLC giving its key characteristics.
Q-3 (a) How does a TDM system manage to convey all the necessary information from a single user, even though
the user signal is only samples?
What is the need for Synchronization in TDM? What are the two common ways of achieving this?
(b) A system is designed to handle 25 users via TDM. Each user signal takes 1-ms time slot. The user
identifier takes 2-ms.
i) Sketch the output of the multiplexer system for the first 10 users.
ii) What percentage of the time is devoted to user identifiers? Does it vary with the number of users?
iii) How many times per second can any given user be transmitted?
(c) What is Manchester Encoding? Compare the bandwidth it uses to that of the NRZ. What are the advantages
of Manchester encoding?
OR
Q-3 (a) State the Nyquist Sampling Theorem and describe its uses in determining how many users a TDM system
can support?
(b) A System is converting voice signals to digital format and then multiplexing many such identical signals.
Each signal is a 3 KHz bandwidth voice signal. It is sampled at twice the Nyquiat rate. The ADC is a 10 bit
unit.
i) What is the sampling rate for each signal?
ii) How many bits per second does each signal cause after it is digitized?
iii) What clock rate is needed for the multiplexing if there are eight identical users?
Section II
Q-4 Explain the concept of CRC checksum for error detection in Data Communication systems giving a suitable
example.
Q- 5 Compare the operation of command/response, interrupt-driven, token passing and CSMA/CD access, with
respect to efficiency, reliability, predictability and cost.
OR
Q-5 (a) Compare RS-232, RS-422 and RS-423 in terms of the following:
Bit-rate, distance, single-ended vs. differential signals, no. of users, voltage levels.
(b) How is handshaking avoided in current loop systems? Why is isolation sometimes needed? How does a
current loop easily provide this?
Q-6 Write notes on any three of the following:
1. MODEMS
2. 7 layer OSI Standard
3. Pulse Dialing Method in telephone systems
4. UART IC 8251
5. ISDN
