Kerala University B.Tech Computer Science Sixth Semester Computer Communication Previous Questions 2003 Scheme

COMPUTER COMMUNICATION

MODULE 1

> What is intersymbol interface in a communication channel? (5)
> Calculate the highest bit rate of a transmission line with a bandwidth of 4500Hz and SNR of 3162(5)
> What is diversity in microwave communication systems?Explain different diversities(10)
> Find the thermal noise power in watts for an electronic communication device operating at room temperature with a bandwidth of 20 KHz(5)
> What do you mean by impulse noise? Demonstrate its effect on digital data by giving an example(8)
> What is white noise(5)
> Derive an expression for noise bandwidth(10)
> Explain various noises in communication systems(9)
> What is the thermal noise level of a channel with a bandwidth of 10KHz carrying 1000 Watts of power operating at 500c?(12)
> Define the following terms with respect to a channel(8)
* Data rate
* Bandwidth
* Noise
* Bit Error Rate
> Differentiate synchronous and asynchronous data transmission methods.(6)
> Asynchronous Transmission(10)
> Synchronous transmission(10)
> Explain the main features of four guided transmission media(20)
> Discuss the characteristics of wireless media(20)
> Digital transmission is preferred over Analog transmission. Give the reasons(8)
> Give the block diagram for a simplified data communication model and explain(12)
> Explain the important features of optical fiber as a guided transmission media(12)
> Explain the important aspects of twisted pair and coaxial cable(12)
> Derive an expression for information rate(10)
> Discuss the various impairments in transmission media(10)
> Explain the three transmission impairments. How they can be controlled(20)
> State and explain sampling theorem(5)
> A digital signaling system is required to operate at 9600 bps. If a signal element encodes a 4 bit /8 bit words, what is the minimum required bandwidth of the channel(12)
> What is the channel capacity for a teleprinter channel with a 300 Hz bandwidth and SNR of 3dB?(8)
> Describe terrestrial microwave communication(8)
> Explain the physical features, transmission characteristics and applications of a terrestrial microwave system.(8)
> Draw and explain the various configurations used in satellite microwave systems.
> What is a VSAT? Describe.
> Explain the important aspects of any two broadband channels with suitable diagrams(20)

MODULE 2

> Determine the minimum number of bits required in a PCM code for a dynamic range of 90 dB. What is the coding efficiency?(10)
> Why should PCM be preferable to DM for encoding analog signals that represent digital data?(8)
> State the sources of noise in a PCM system(5)
> What is non-linear encoding in PCM(5)
> Describe companding and its advantages(5)
> A 3.3 KHz voice signal is sampled once every 125µsec and uses a 512 level quantizer. How many bits are transmitted per second?(6)
> Explain the following PSK.(10)
* BPSK
* QPSK
* 8-PSK
* 16-PSK
> What is the bandwidth efficiency for FSK, ASK, PSK and XPSK for a bit error rate of 10-7 on a channel with SNR 12 dB?(12)
> What is multiplexing? Why is it needed?(5)
> With relevant diagrams, explain TDM, FDM and WDM in detail(15)
> Describe the following(20)
* FDM
* Synchronous TDM
> Compare TDM and FDM.(10)
> How is link control carried out in a TDM system(8)
> Eleven sources are to be multiplexed on a single link using synchronous TDM. The first two sources are analog with 2 KHZ bandwidth, the third one is also analog but with 4KHz bandwidth and the balance eight are 7200 bps synchronous digital sources. Draw and explain how TDM can be implemented and calculate the typical composite bit rate.(12)
> Compare synchronous and asynchronous transmission(10)
> Encode the binary stream 01001100011 into NRZ-L, NRZ-I, Bipolar-AMI and Manchester schemes.(10)
> Encode the following bit stream into NRZ and Biphase encoding schemes 0101011110000(10)
> Explain the important aspects of the following
* NRZ-L encoding
* NRZ-I encoding
* Bipolar- AMI encoding
* Pseudoternary encoding
* Manchester encoding
* Differential Manchester encoding
Give the signal for each of the above encoding techniques for the digital data 11010011 (20)
> Explain two scrambling techniques used to overcome the demerits of Bipolar AMI encoding(12)
> Explain the working of delta modulation(10)
> Explain what do you mean by slope overload error and quantization error in Delta modulation(8)
> Derive an expression for the transmitted signal in the case of AM and FM(20)
> Describe the different types of Analog to Analog encoding techniques(15)
> What is the increase in SNR for 1 bit increase in A/D conversion?(12)
> With relevant waveforms, explain different encoding methods(20)
> Explain frequency shift keying(5)
> With neat sketches, explain QAM(10)
> Explain Delta modulation.(8)
> Discuss the following noise sources in detail.(20)
* Thermal
* Intermodulation
* Crosstalk
* Impulse

MODULE 3

> Explain the operation of crossbar switches.(5)
> Describe the forward error detection methods(7)
> Discuss the methods of generating convolution codes(8)
> Compare circuit switching, packet switching and message switching in terms of working concepts and performance.(12)
> Describe the following
* Circuit Switching(10)
* Packet Switching(10)
> Give important aspects of circuit switching(8)
> Give important aspects of packet switching(8)
> Compare the various ARQ techniques(8)
> Discuss the various ARQ schemes(8)
> Describe the Go-Back-N ARQ scheme(10)
> Suppose that a selective-reject ARQ is used where N=4. Show, by example, that a 3-bit sequence number is needed.(10)
> A channel has a data rate of 8kpbs and a propagation delay of 20ms. For what range of frame sizes does stop -and – wait give and efficiency of at least 50%?(10)
> Consider the use of 1000 bit frames on a 1 Mbps satellite channel with 270 ms delay. What is the maximum link utilization for stop and wait flow control?(10)
> For P=100111 and M=111100001, find the CRC(10)
> Obtain the CRC sequence for a message sequence M=110011 and polynomial sequence P=11001.(10)
> Explain the Digital logic implementation of CRC(12)
> Briefly describe the mathematical principles used in the design of CRC.(10)
> List the various categories of errors that are detectable if CRC is used(5)
> What is CRC? With a suitable example explain the CRC-16 code generation and checking.(20)
> Using the CRC- CCITT polynomial, generate the 16 bit CRC code for a message consisting of a 1 followed by 15 zeros(10)
> Error detection and retransmission is more often used than error correction at the receiver- Discuss(5)
> For P=110011 and M= 11100011, find the CRC(10).
> Using modulo-2 CRC compute the FCS for the following case(8)
* Data bit (D) = 1010001101
* Divisor (P) = 110101
> Suggest improvements to the bit stuffing algorithm to overcome the problems of single bit errors(10)
> If the bit string 0111101111101111110 is subjected to bit stuffing, what is the output string?(10)
> What is error correction and detection codes?(5)
> With a suitable example, explain error correction using Hamming code(15)
> Explain error correction using block codes.(12)
> Explain clearly block codes for error correction(12)
> Two stations communicate via a 1 Mbps satellite link with a propagation delay of 270 ms. The satellite serves merely to retransmit data received from one station to another with negligible switching delay. Using HDLC frames of 1024 bits with 3 bit sequence numbers, what is the maximum possible data throughput (not counting overhead bits)?(12)