DipIETE – ET (OLD SCHEME)

Code: DE20 Subject: ELECTRONIC SWITCHING SYSTEMS

Time: 3 Hours Max. Marks: 100

NOTE: There are 9 Questions in all.

· Question 1 is compulsory and carries 20 marks. Answer to Q.1 must be written in the space provided for it in the answer book supplied and nowhere else.

· Out of the remaining EIGHT Questions, answer any FIVE Questions. Each question carries 16 marks.

· Any required data not explicitly given, may be suitably assumed and stated.

Q.1 Choose the correct or the best alternative in the following: (210)

a. In a telephone channel, bandwidth is 3 kHz, SNR is 30 dB. The maximum bit rate of the channel is _______.

(A) 40 bps (B) 30 bps

(C) 40 kbps (D) 30 kbps

b. In a circuit switched system _________.

(A) data is first transferred and then the receiver is connected to the source

(B) data is first divided into small blocks and then transferred

(C) the circuit connection is first made complete & then data is transferred

(D) None of the above

c. In a strowger switching system, the testing circuit _________.

(A) tests the circuit for faults

(B) hunts and seizes control of the circuit for conversation

(C) searches only for a free outlet circuit

(D) tests only the free condition of the circuit

d. In a crossbar switching circuit with 8 subscribers, the number of switching elements equals to________.

(A) 16 (B) 256

(C) 4096 (D) 16384

e. In a time multiplexed space switch, with 32 channels, memory access time of 100 ns and transfer time of 100 ns, the number of trunks that can be supported is ________.

(A) 20 (B) 30

(C) 25 (D) 35

f. Unvoiced sounds are generated due to _________.

(A) vibration of vocal chords

(B) expelling of air through lips and teeth

(C) expelling air through nose

(D) none of the above

g. Microwave communication involves __________.

(A) frequency range between 15 MHz & 150 GHz

(B) line of sight communication

(C) time sharing techniques

(D) all of the above

h. Busy hour call attempt _________.

(A) is the number of calls attempted during busy hour

(B) determines the processing capacity of an exchange

(C) is counted when someone makes a call during busy hour

(D) All of the above

i. In an OSI model the media for data transmission __________.

(A) is connected to the transport layer

(B) is connected to the data link layer

(C) is connected to the physical layer

(D) All of the above

j. The highest link to link layer is ________.

(A) network layer (B) transport layer

(C) data layer (D) physical layer

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2 a. With the help of a block diagram, explain the OSI reference model. (8)

b. What are the various signalling tones available for a telephone exchange? Briefly explain each tone along with its frequency range. (8)

Q.3 a. Explain the process of quantization of analog signals. How is the process different from sampling? What are the side effects of reducing the quantization error? (8)

b. With the help of a block diagram explain how a subscriber connects to another subscriber in a crossbar exchange? (8)

Q.4 a. In an exchange 60 subscribers initiate calls in 30 mins. The total duration of the calls is 6000 secs. Calculate the load offered to the network and the average subscriber traffic. (8)

b. An exchange uses a 40 volt battery. A resistance of 200 Ω is used in series for protection. Determine the farthest distance a subscriber can be located if the telephone used offers a DC resistance of 50 Ω. The microphone requires a current of 23 mA for its functioning. The wire used is of 24 AWG. (8)

Q.5 a. What are the different types of store and forwarding networks? Explain the differences between the types of store and forwarding networks. (8)

b. What is DID? How does DID work? (8)

Q.6 a. How does the physical link layer work? Explain the various signal conversion in the physical link layer. (8)

b. Compare the three topologies used for implementation of LAN. (8)

Q.7 a. Give a brief comparison of satellite communication and terrestrial communication. (8)

b. What is “singing” in a transmission line? Why does singing occur? (8)

Q.8 a. What are loading coils? What is the need of loading coil in a telephone exchange? (8)

b. Explain the concept of ionospheric communication. (8)

Q.9 Write short note on any TWO of the following: (82)

(i) Circuit Switching & Packet switching.

(ii) Token ring system of data transmission.

(iii) TDM and FDM.

(iv) DTMF Signalling.