DEPARTMENT OF ELECTRONICS & COMM. ENGG.
B.I.T. MESRA, RANCHI
EC7101 TELECOMMUNICATION SWITCHING CIRCUITS & NETWORKS
Switching in Telecommunication Systems:
Evolution of Telecommunications, General principle of switching, Classification of Switching Systems, Elements of Switching System, Signalling tones, DTMF, Common Control and Direct Control.
"Telecommunication Switching Systems & Networks", by T. Viswanathan, PHI, 2001.
Module – 2:
Electronic Space Division Switching:
Stored Program Control (SPC), Centralised SPC, Distributed SPC, Enhanced Services, Two-Stage Networks, Three-Stage Networks.
"Telecommunication Switching Systems &Networks", by T. Viswanathan, PHI, 2001. (Chap.4)
Module – 3:
Time Division Switching:
Basic Time Division Space Switching, Time Multiplexed Space Switching, Time Multiplexed Time Switching, Combination Switching, Three-stage Combination Switching.
"Telecommunication Switching Systems & Networks", by T. Viswanathan, PHI, 2001. (Chap. 6)
Module – 4:
Network Traffic Load and Parameters, Grade of Service and Blocking Probability, Modelling Switching systems, Blocking Models & Loss Estimates, Delay Systems.
"Telecommunication Switching Systems", by T. Viswanathan, PHI, 2001. (Chap 8)
Module – 5:
ISDN and its Motivation, New Services, Network and Protocol Architecture, Transmission Channels, Internetworking, BISDN.
"Telecommunication Switching Systems & Networks", by T. Viswanathan, PHI, 2001. (Chap 11)
Module – 6:
Network Subscriber Loop Systems, Switching Hierarchy & Routing, Transmission Plan, Numbering Plan, National Schemes, International numbering.
1. "Telecommunication Switching Systems & Networks", T. Viswanathan, PHI, 2001. (Chap. 9)
2. "Telecommunications Switching, Traffic and Networks", J. E. Flood, Chap. 10, Pearson Education Asia, 2004.
Module – 7:
Introduction to Asynchronous Transfer Mode (ATM), Protocol, Architecture, ATM Logical Connection, ATM Cells, Transmission of ATM Cells, ATM Adaptation Layer, Traffic and congestion control.
"Data & Computer Communications by William Stallings", 7/e, PHI. (Chaps – 11 & 12)
EC7101 TELECOMMUNICATION SWITCHING SYSTEMS & NETWORKS
1. Classify and explain different types of switching systems.
2. Draw the diagram of carbon granule microphone and derive the equation of voice-modulated current from the microphone.
3. Explain simplex, half duplex & full duplex communication systems and give at least two examples of each.
4. What is sidetone? How it is minimized using antisidetone circuit? Explain with circuit diagram.
5. Explain the following terms:
a. Symmetric network
b. Folded network
c. Blocking network
d. Non-blocking network
e. Blocking Probability
f. Busy-hour traffic
g. Transit Exchange
h. Erlang (E)
6. Name and explain different types of signalling tones.
7. What are the elements of a switching system? Explain using diagram.
8. Explain with suitable diagram the working of manned Common Battery exchange.
9. Compare and contrast between local battery exchanges and common battery exchanges.
10. What do you understand by PABX and DID (Direct Inward Dialling)?
11. What are the drawbacks of manual exchange?
12. Give the drawbacks associated with local battery exchange.
13. An electrical communication system uses a channel that has 20dB loss. Estimate the received power, if the transmitted power is one watt.
14. Estimate the rate of transmission for a channel used to connect 20,000 telephone subscribers (use voice B.W = 4 KHz and 1 sample = 8 bits).
15. If the noise power in a channel is 0.1dBm and the signal power is 20mw, what is the S/N ratio?
16. What is the importance of sidetone in a telephonic conversation?
17. Estimate the bandwidth requirements of a single satellite that is to support 10-lakh telephone conversations simultaneously.
18. A central battery exchange is powered with a 48V battery. The carbon microphone requires a minimum of 24mA as energizing current. The battery has a 4.0ohm resistance in series for short circuit protection. The D.C. resistance of the microphone is 50ohm. If the cable used for subscriber lines has a resistance of 50ohm/km, determine the maximum distance at which a subscriber station can be located.
19. For a carbon granule microphone, determine a suitable value for m, if the contribution from each of the higher order terms is to be less than 0.01 Io.
20. What is the importance of a steady current flowing through a carbon microphone?
21. A 1000 line exchange is partly folded & partly non-folded. Forty percent of the subscribers are active during peak hour, if the ratio of local to external traffic is 4:1, estimate the number of trunk lines required.
22. What are the advantages of Automatic switching systems?
23. Differentiate between pulse dialling and multifrequency dialling.
24. Give the advantages of multifrequency dialling over pulse dialling of rotary dialling.
25. Draw the pulse dialling waveform for 24.
26. Calculate the time required to dial 00-91-44-414630 using a rotary dial telephone. Assume that the subscriber takes 6000ms on an average to rotate the dial for a single digit.
27. Name the basic circuits used in all the selector control circuits.
28. A busy tone does not imply that the called party is actually engaged in a conversation. Explain.
29. A long distance dialer hears four different types of call-in-progress signals while establishing call. What can be concluded?
30. Describe the working of a rotary switch. Differentiate between forward acting and reverse acting types.
31. Differentiate between common control and direct control.
32. Explain the function of touch dial arrangement.
33. What is dual tone multifrequency (DTMF) signalling? What are its advantages?
34. What is the series of tones that are sent when dialling the number 911 in DTMF Touch Tone Pad?
1. Blocking crossbar switch is to be designed to support 1000 subscribers. If the estimated peak traffic is 10 Erlangs with average holding time of three minutes per call, estimate the number of cross points required.
2. Explain centralized stored program control (SPC).
3. Differentiate between centralized & distributed SPC.
4. Describe various configurations of dual processor architecture.
5. Given that MTBF = 2000 hrs & MTTR = 4 hrs. Calculate the unavailability for single and dual processor systems.
6. Derive the expression for the switching elements for two stage and three stage networks.
7. For a Close network derive the expression for minimum number of switching elements.
Module – 3:
1. Explain basic time division space switching and time division time switching.
2. Explain different types of combination switching.
i. Time space
ii. Space time
iii. Time space time
iv. Space time space.
3. In a time space switch M = 128, N = 16 & the number of subscribers connected to the system is 0.1 MN. Determine the blocking probability of a switch if
(a) all the subscribers are active at the same time
(b) Only 5-% of the subscribers are active simultaneously.
Module – 4:
1. Explain the following terms:
a. Busy hour
b. Peak busy hour
c. Time consistent busy hour.
2. An exchange serves 2000 subscribers. If the average BHCA is 10,000 & CCR is 60%, calculate the busy hour calling rate.
3. Over a 20-minute observation interval, 40 subscribers initiate calls. Total duration of the calls is 4800 sec. Calculate the load offered to the network by the subscribers and the average subscriber traffic.
4. Show that grade of service (GOS) is equal to blocking probability for erlang traffic.
5. Derive the expression for GOS for Engest traffic.
6. A call processor in an exchange requires 120 ms to service a complete call. What is the BHCA rating for the processor? If the exchange is capable of carrying 700 erlangs of traffic, what is the call completion rate? Assume an average call holding time of two minutes.
7. Explain the following:
(a) Grade of service
(b) Blocking probability
(c) Delay probability
8 A switching system serves 10,000 subscribers with a traffic intensity of 0.1E per subscriber. If there is a sudden spurt in the traffic increasing the average traffic by 50%. What is the effect on the arrival rate?
9 10,000 subscribers are connected to an exchange. If the exchange is designed to achieve a call completion rate of 0.8 when the busy hour calling rate is 4.8, what is the BHCA that can be supported by the exchange. What should be the call processing time for this exchange?
10 In an exchange, the calls arrive at the rate of 1100 calls per hour, with each call holding for duration of three minutes. If the demand is serviced by a trunk group of 50 lines, determine the GOS.
11 Derive the expression for the switching elements and blocking probability of a three-stage network.
12 A telephone administration provides leased lines at the rate of Rs. 600 per Km for a minimum rental period of 3 months. A heavy point-to-point traffic user has his offices located 600 Km apart and is confronted with the choice of using STD or leased lines. At what traffic volume per day should he move over to leased line? Assume 20 working days per month and a rate of Re. 1 per unit recorded by the meter.
13 A telephone exchange supporting 5000 subscribers uses DTMF dialling and a common control subsystem with 100 digit receivers. Each digit receiver is assigned for duration of five seconds per subscriber for call processing. If 20% of the subscribers attempt to call simultaneously, what is the worst-case wait time for a subscriber before he receives the dial tone?
14 Estimate the number of cross points required to design an exchange that supports 500 users on a non-blocking basis and 50 transit, outgoing or incoming calls simultaneously.
15 Explain the differences between micro programmed control unit and hard-wired control unit.
16 How many subscribers can be supported in bi-directional PAM switching bus, if the pulse width of the PAM sample is 125 ns?
17 Derive an expression for the blocking probability of a TSTS switch if each stage is individually non-blocking.
18 An exchange serves 2000 subscribers. If the average BHCA is 10,000 and the CCR is 60%, calculate the busy hour calling rate.
19 In a group of 10 servers, each is occupied for 30 minutes in an observation interval of two hours; calculate the traffic carried by the group.
20 A group of 20 servers carry traffic of 10 erlangs. If the average duration of a call is three minutes, calculate the number of calls put through by a single server and the group as a whole in a one-hour period.
21 A subscriber makes three phone calls of three minutes, four minutes and two minutes duration in a one-hour period. Calculate the subscriber traffic in erlangs; CCS and CM.
22 Over a 20-minute observation interval, 40 subscribers initiate calls. Total duration of the call is 4800 secs. Calculate the load offered to the network by the subscribers and the average subscriber traffic.
23 In a telephone system, there are 20 servers and 100 subscribers. On an average, there are 10 busy serves at any time. The probability of all the servers being busy is 0.2. Calculate GOS assuming (i) Erlang traffic (ii) Engest traffic.
24 What is on-hook and off-hook? When a subscriber handset goes "off-hook", what occurs at the serving switch?
25 A subscriber pair, with a fixed battery voltage, is extended. As we extend the loop further, two limiting performance factors come into play. Name them.
26 What are the two basic parameters that define "traffic"? Explain them.
27 Distinguish between offered traffic and carried traffic.
28 Distinguish a full availability switch from a limited availability switch.
29 A particular exchange has been dimensioned to handle 1000 calls during the busy hour. On a certain day during the busy hour; 1100 calls are offered. What is the resulting grade of service?
30 Explain holding time and delay with regard to SPC systems.
31 On a particular traffic relation the calling rate is 461 and the average call duration is 1.5 min during the busy hour. What is the traffic intensity in CCS, in erlangs?
32 In traffic theory there are three ways lost calls are handled. What are these? Explain them.
Module – 5:
1. Give the basic principles on which ISDN is based.
2. Explain the factors responsible for the development of ISDN.
3. What are the services that ISDN can support?
4. Explain the processes that take place in E-mail.
5. Explain the ISDN architecture.
6. Explain the signalling used in ISDN.
7. Name & explain the different layers of the ISDN protocol architecture.
8. Explain the following:
(i) Video text (ii) Teletext
(iii) Compare & Contrast telex and e-mail systems
Module – 6:
1. How many wires connect the telephone to the central exchange?
2. What are the names given to the wires connected to the phone?
3. What is a line?
4. What is a trunk?
5. What are the advantages of a central exchange?
6. Discuss the various topologies adopted for interconnecting exchanges.
7. Discuss the CCITT hierarchical structure for routing traffic between exchanges.
8. Discuss the National and International telephone numbering plan.
Module – 7:
1. What is ATM?
2. (a)Explain the cell structure of ATM.
a. Cell header at the B – ISDN UNI and cell header at the B – ISDN NNI.
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