Tsn Qn Bank.docx

UNIT1 - MULTIPLEXING PART A 1.What Is Differential Encoding? Encoding in which signal significant conditions represent binary data, such as \"0\" and \"1\", and are represented as changes to succeeding values rather than with respect to a given reference. Differential encoding is phase-shift keying (PSK) in which the information is not conveyed by the absolute phase of the signal with respect to a reference, but by the difference between phases of successive symbols, thus eliminating the requirement for a phase reference at the receiver. 2. Define Payload Framing? The Multiplexing structure of SONET and SDH has been described in detail. To get useful work out of these different sized containers, a payload mapping is needed, that is, a systematic method for inserting and removing the payload from a SONET/SDH container. Although it is preferable to use standardized mappings for interoperability, a variety of proprietary mappings may exist for various purposes. 3.List out the various transmission system in telecommunication network? 1.Open Wire 2. Paired Cable 3.Pair Gain Systems 4.Define FDM modulation? In analog transmission, signals are commonly multiplexed using frequency-division multiplexing (FDM), in which the carrier bandwidth is divided into sub channels of different frequency widths, each carrying a signal at the same time in parallel. 5. Define line coding? Line coding is the process of converting binary data, a sequence of bits to a digital signal. For example data, text, numbers, graphical images, audio and video that are stored in computer memory are all sequences of bits. Line coding converts a sequence of bits to a digital signal. Some line coding schemes leave a residual direct-current (DC) component (zero-frequency). This component is undesirable for two reasons. First, if the signal is to pass through a system (such as a transformer) that does not allow the passage of a DC component, the signal is distorted and may create errors in the output. Second, this component is extra energy residing on the line and is use 7. What is digital biphase? A data recovery system for deriving digital data from a bi phase encoded stream wherein signal transition occurs at mid-bit or bit boundary having an edge detector for detecting the occurrence of each fallen edge of a data stream, an edge decoder connected to the detector for determining the time between

successive falling edges, a falling edge identifier connected to the edge decoder for determining whether a detected fallen edge occurs on a bit boundary or at a mid-bit, a falling edge memory connected to the falling edge identifier for remembering whether the previous falling edge occurred at a bit boundary or at mid-bit, a data decoder connected to receive input from the falling edge memory and the edge decoder, and having logic for determining the recovered data according to a table in which the data is identified in response to the occurrence at a bit boundary or at mid-bit and a selected spacing between falling edges. 8. Draw the frame format of STS-1 level? 9. What is Virtual Tributaries? VT structures can be individually assigned to carry one of four types of signals. Dependin on the data rate of a particular signal, more than one signal may be carried within a Vt structure as a group. 10. What short notes on SONET networks? Gate way network elements provide interfaces to external digital signals.These signals are mapped and unmapped by the gate way using the mapping format.Only bit stuffing used to synchronize the asynchronous tributaries to SONET. 11. Write down concept of freq justification? When the input data has a rate lower than the output data rate of a multiplexer, the positive stuffing will occur. The input is stored in a buffer at a rate which is controlled by the WRITE clock. Since the output (READ) clock rate is higher than the WRITE clock rate, the buffer content will be depleted or emptied. To avoid this condition, the buffer fill is constantly monitored and compared to a threshold. If the the content fill is below a threshold, the READ clock is inhibited and stuffed bit is inserted to the output stream. Meanwhile, the input data stream is still filling the buffer. The stuffed bit location information must be transmitted to the receiver so that the receiver can remove the stuffed bit. 12.Draw the block dig of SONET system? 13. Compare synchronous and statistical time division multiplexing. Plesiochronous digital hierarchy (PDH) was developed as a standard for multiplexing higher order frames. PDH created larger numbers of channels by multiplexing the standard Europeans 30 channel TDM frames. This solution worked for a while; however PDH suffered from several inherent drawbacks which ultimately resulted in the development of the Synchronous Digital Hierarchy (SDH). The requirementsSTDM is an advanced version of TDM in which both the address of the terminal and the data itself are transmitted together for better routing. Using STDM allows bandwidth to be split over 1 line. Many college and corporate campuses use this type of TDM to logically distribute bandwidth.If there is one 10MBit line coming into the building, STDM can be used to provide 178 terminals with a dedicated 56k connection (178 * 56k = 9.96Mb). A more common use however is to only grant the bandwidth when that much is needed. STDM does not reserve a time slot for each terminal, rather it assigns a slot when the terminal is requiring data to be sent or received.This is also called asynchronous time-division multiplexing(ATDM). 14.What is meant by data scrambling?

Data communication system and method with a data scrambling with high security. A data scrambling part is provided with a extended key memory for storing addresses of extended keys, and one of the extended keys is used as a parameter for scrambling an input data to be scrambled. In order to select one of the extended keys to be input to each processing block for converting the input data by using the parameter to output converted data, a selector varies the address of the extended key depending on a plaintext of the input data. PART B 1. Explain the concept of FDM multiplexing & TDM? 2. Write about SONET frame format? 3. Describe the ds3 pay load mapping and e4 payload mapping? 4. Explain the concept SONET rings? 5. Explain the working operation and administration of SONET systems? 6. Explain the following terms (i) TDM loops and rings (ii) Bit interleaving versus word interleaving ( iii ) Binary N – zero substitution 7. Explain the functions of SONET multiplexing and networks? 8. Discuss about the concept of digital transmission and multiplexing? 9. Draw and explain time division multiplex loops and rings. 10. Give a brief notes on binary N Zero substitution 11. State the advantages and disadvantages of partial response signaling. 12. Draw and explain the opearation of unidirectional patch switched and bi-directional line switched SONET rings. 13. Give a brief note on operation, administrative and maintenance features of SONET. UNIT 2 DIGITAL SWITCHING PART A 1. What is the need of multidimensional switching? A multidimensional switching that utilizes at least three degrees of freedom, time, wavelength and space. In one embodiment that involves point-to-point switching, each space channel between an input and an output is assigned a time slot and wavelength coordinate characteristic of the output and the input transmitter and output receiver are tuned to the appropriate time and wavelength coordinates and selective switching is used to complete the space channel between the input and output. 2. What is switching system? Based on the principles of time-division multiplexing of digitized analog signals. An electronic switching system digitizes analog signals from subscriber loops, and interconnects them by assigning the digitized signals to the appropriate time slots. It may also interconnect digital data or voice circuits. A

switching system with major devices constructed of semiconductor components. A semi-electronic switching system that had reed relays or crossbar matrices for its talk paths, as well as semiconductor components, was also considered to be an ess in the 20th century. 3. Define time switching? A time switch is an electric switch with a built-in clock that plugs into an electric socket, between the socket itself and a power plug. This physical arrangement allows the connected device(s) to automatically receive power for a desired duration of time. There are also time switches with several power plugs that can be independently programmed to turn on and off at specified times. 4. Define space switching? The simplest switching structure is a rectangular array of cross points. The switching matrix can be used to connect any one of N inlets two any one of M outlets. 5. Define Multiplexing? In multiplexing is a process where multiple analog message signals or digital data streams are combined into one signal over a shared medium. The aim is to share an expensive resource. For example, in telecommunications, several phone calls may be transferred using one wire. It originated in telegraphy, and is now widely applied in communications.The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. 6. Define path finding? Determining a path through a single stage switch is virtually automatic since the necessary cross point is uniquely specified by the inlet-outlet pair to be connected 7. What is non-blocking switching? A single Stage Switch is that it is strictly non blocking it is the main feature of this switching. If the called party is idle, the desired connection can always be established by selecting the particular cross point dedicated to the particular input output pair 8. Draw the lee graph of 3 stage switching network? Refer Book Digital Telephony Third Edition Page No 235 Fig 5.8 9. Draw the circuit diagram of folded four wire switches? Refer Book Digital Telephony Third Edition Page No 242 Fig 5.11 10. What is BORSCHT? The Complete list of the Interface Requirement for a digital switch interface is Known as BORSCHT. B-Battery Feed

O-Overvoltage Protection R-Ringing C-Coding H-Hybrid T-Testing 11. What are the functions of TSI circuit? The exchange of information between two different time slots is accomplished by time slot interchange. The data words in incoming time slots are returned into sequential location of the data’s store memory 12. Write short notes on switch matrix control? When an available path through a common control switching network is determined, the control element of the switch transfers. The necessary information to the network to select the appropriate cross points. 13. Draw the circuit diagram of 4-wire digital switch? 14. Why higher sampling rates are preferred in analog time division switching? When connecting two wires in analog line, the two interfaces are necessarily implemented in a common module. The first controls gating of inputs on to the bus one sample at a time. 15. How the control memory in TS switches implemented? In case of solid state electronic switching matrix the general and the time division switching in particular, the no of cross points alone is a less meaningful measure of implementation cost. 16. Define time division switching. Time Division Switching is equally applicable to either analog or digital signals. When the cross points are shared in this manner much greater savings in cross points can be achieved. 17. Define Electronic Switching. The use of computers to control the switching functions of a central office lead to the ESS Or Electronic Automatic Exchange 18. Define Digital Switching. First digital switching did not use the program control. Digital switching was first introduced in the US network 1976 with AT and TS.

PART B 1. Explain the following 1. STS switching 2) TST switching. 2. Explain the principle of time division switching. 3. Discuss the concept of switch matrix control. 4. Explain in detail about No.4 ESS toll switch. 5. Discuss about the concept of two dimensional switching network. 6. Explain in working operation of digital memory switch? 7. Explain the concept of digital switching in an analog environment? 8. Explain the operation and features of No.4 ESS toll switch with a neat diagram. 9. Discuss the operation and application of digital cross connect system. 10. Write about digital switching in analog environment. 11. Discuss the operation and application of digital cross connect system. 12. Explain the S-T-S combination switching with necessary diagrams. 13. Draw and explain a three stage non blocking switching matrix and derive an expression for the minimum number of cross points required for non blocking operation. 14. Discuss the Lee’s method of blocking probability analysis. 15. Discuss the operation of TST switch with a neat diagram

UNIT- 3 NETWORK SYNCHRONIZATION CONTROL AND MANAGEMENT PART A 1. List out the timing inaccuracies? Slips Slip rate Asynchronous multiplex 2. Define clock instability? The variation in the output frequency is called clock instability.

3. What is Doppler shift? The most significant source of potential timing instability received clock occurs as a result of Doppler shifts from air planes or satellites. the Doppler shift occurs in essence as a result of path change. 4. What are elastic stores? In case of noise and interference induced jitter, the change in bit store occurs because the data are sampled at little earlier or little latter than nominal. 5. What is the application of elastic store? Clock offsets Unsynchronized clocks Sustained clock Instability in received clock 6. Define slip rate? The difference between the Elastic store input data rate and its output data rate is known as slip rate 7. What is waiting time jitter? The Jitter is commonly specified by the communication theorist as a power measurement.

8. List out the various approaches used in synchronizing a digital network? Network Synchronizing can also specify how the various nodes respond to degradation are complete failure of their references. Abrupt switch over often occur in the stratum four nodes can cause phase transients in the output clock. 9. Define time interval error? A TIE is the difference in delay between a ideal timing signal measured at the end of a particular time period an MITE is the maximum peak to peak variation. 10. Define timing jitter. When De Multiplexing high level TDM it is necessary to generate a clock for each derived sub channel. Because the sub channels are transferred as a synchronies data stream 11. Define an elastic store and also give its application.

A functional model of an multiplexer is associated with each lower level input is an elastic store to hold incoming data until it is transferred to the higher level output. 12. What is meant by Pulse Stuffing? In the Essence the TDM links of the network would provide TDM Channels through which user data flows at lower and variable rates the difference being absorbed by the pulse stuffing. PART B 1. Describe in details about 1. Phase locked loop 2.Jitter measurements 3.Systematic jitter. 2. Explain the concept of network control and network management? 3. With suitable block diagram explain the function of jitter removing regeneration repeater 4. Discuss in details about timing in accuracies? 5. Explain the working operation of M12 multiplexer. 6. Explain the concept of network synchronization? 7. Discuss about the concept of network timing performance measurement. 8. Discuss the main sources of clock instability in a digital network. 9. Discuss the principle of network control and management.

10. Enumerate the different approaches of synchronizing digital networks. 11. Explain the major sources that cause clock instability in digital networks. 12. Write a brief note on flow control in telecommunication networks. 13. Explain the different approaches used in network synchronization. UNIT 4 DIGITAL SUBSCRIBER ACCESS PART A 1. Differentiate ADSL and VDSL. ADSL allows for high data rates to the subscriber and moderate to low rate to low rates from the subscriber to the network. ADSL channels are separated from the public network at the line interface of the PSTN.

2. Write the concept of PCM modem operation. A method and apparatus is provided for robust measuring of the communications channel in which the digital modem\'s transmitter is silenced during generation of training signals by the analog modem, with the silencing of the digital modem\'s transmitter eliminating problems associated with echo during channel measurement at the digital modem. The above method thus eliminates echo during channel estimation and removes any dependencies on the performance of the echo canceller normally used. 3. What is ADSL? Asymmetric digital subscriber line (ADSL) is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voice band modem can provide. It does this by utilizing frequencies that are not used by a voice telephone call. A splitter or micro filter - allows a single telephone connection to be used for both ADSL service and voice calls at the same time. ADSL can generally only be distributed over short distances from the central office, typically less than 4 kilometres (2 mi) but has been known to exceed 8 kilometres (5 mi) if the originally laid wire gauge allows for farther distribution. 4. Define ISDN? Integrated services digital network is a set of communications standards enabling traditional telephone lines to carry voice, digital network services, and video. Prior to ISDN, the phone system was viewed as a way to transport voice, with some special services available for data. The key feature of the ISDN is that it integrates speech and data on the same lines, adding features that were not available in the classic telephone system. There are several kinds of access interfaces to ISDN defined as basic rate interface (BRI), primary rate interface 5. List out 2 principles of ISDN? The ISDN is intended to be a single, uniformly accessible, worldwide network » It is intended to replace the current public telecommunications network and computer networks. » It is already in its second generation without achieving the universal deployment hoped. 6. Name some services provided by ISDN. Integrated services refer to ISDN\'s ability to deliver at minimum two simultaneous connections, in any combination of data, voice, video, and fax, over a single line. Multiple devices can be attached to the line, and used as needed. That means an ISDN line can take care of most people\'s complete communications needs at a much higher transmission rate, without forcing the purchase of multiple analog phone lines. 7. List out the various features of ISDN B channel? A B channel is a 64-Kbps unit of clear digital bandwidth. Based on the data rate required to carry one digital voice conversation, a B channel can carry any type of digital information (voice, data, or video) with no restrictions on format or protocol imposed by the ISDN carrier.

8. List out the various features of ISDN D channel? A D channel is a signalling channel. It carries the information needed to connect or disconnect calls and to negotiate special calling parameters (i.e., automatic number ID, call waiting, data protocol). The D channel can also carry packet-switched data using the X.25 protocol. The D channel is not a clear channel. It operates according to a well-defined pair of layered protocols: 9. Write short notes on basic rate and primary rate access to ISDN. Basic Rate Access is based on new technology conceived especially for ISDN. Designed to provide service to individual users or small businesses, Basic Rate Access provides two 64-Kbps B channels and one 16-Kbps D channel Primary Rate Access, which is based on pre-ISDN digital carrier technology, is designed to provide highcapacity service to large customers for applications such as PBX-to-PBX trunking. There are two kinds of Primary Rate Access: 23B+D and 30B+D. Each depends on the kind of digital carrier available in a given country. 10. What is S bus? The ISDN S Bus is a 4-wire digital bus, with iso- lated transmit and receive pairs. This invention uses these isolated pairs to establish an analog signal path between extension phones on the S Bus. This permits these phones, up to the maximum of 8 allowed on the S Bus, to be conferenced on the S Bus and to be conferenced into the ISDN system. Circuitry is provided to maintain constant audio levels regardless of the number of exten- sion phones in use. 11. Write notes on fiber in the loop? Fiber in the loop designed to provide a media of return patch for a fiber optic signal; typically it is used for fiber optic testing applications or network restorations. For the testing applications, the loopback signal is used for diagnosing a problem. Sending a loopback test to network equipment, one at a time, is a technique for isolating a problem. Similar as fiber optic patch cords, fiber loopback can be with various jacket types and cable diameters, and they can be with different terminations and length. 12. What is LMDS local microwave distribution service? LMDS commonly operates on microwave frequencies across the 26 GHz and 29 GHz bands. In the United States, frequencies from 31.0 through 31.3 GHz are also considered LMDS frequencies. LMDS was conceived as a broadband, fixed wireless, point-to-multipoint technology for utilization in the last mile. Throughput capacity and reliable distance of the link depends on common radio link constraints and the modulation method used - either phase-shift keying or amplitude modulation. In general deployment links of up to 5 miles (8 km) from the base station are possible, but distance is typically limited to about 1.5 miles (2.4 km) due to rain fade attenuation constraints. Some point-to-point systems also use the LMDS frequencies and can reach slightly farther distances due to increased antenna gain 13. What is PCM modem?

In a full duplex PCM modem system, a method and apparatus is provided for robust measuring of the communications channel in which the digital modem\'s transmitter is silenced during generation of training signals by the analog modem, with the silencing of the digital modem\'s transmitter eliminating problems associated with echo during channel measurement at the digital modem. The above method thus eliminates echo during channel estimation and removes any dependencies on the performance of the echo canceller normally used. 14. State any two basic features of ISDN – B channels. A B channel is a 64-Kbps unit of clear digital bandwidth. Based on the data rate required to carry one digital voice conversation, a B channel can carry any type of digital information (voice, data, or video) with no restrictions on format or protocol imposed by the ISDN carrier. 15. Write the features and applications of VDSL. VDSL (Very High Speed Digital Subscriber Line 2) is that exploits the existing infrastructure of copper wires that were originally deployed for POTS. It can be deployed from central offices, from fibrefed cabinets located near the customer premises, or within buildings. VDSL2 is the newest and most advanced standard of DSL broadband wireline communications. Designed to support the wide deployment of Triple Play services such as voice, video, data, high definition television (HDTV) and interactive gaming. VDSL2 is purported to enable operators and carriers to gradually, flexibly, and cost efficiently upgrade existing xDSL-infrastructure. 16. What are the functions of ISDN U interface? The U interface is a two-wire interface between the exchange and a network terminating unit, which is usually the demarcation point in non-North American networks.

17. Compare FTTH and FTTC. Fiber optic cables are made of glass fiber that can carry data at speeds exceeding 2.5 gigabits per second (gbps). FTTH services commonly offer a fleet of plans with differing speeds that are price dependent. At the lower end of the scale, a service plan might offer speeds of 10 megabits per second (mbps), while typical DSL (Digital Subscriber Line) service running on existing copper lines is 1.5 mbps. A more expensive FTTH plan might offer data transfer speeds of over 100 mbps —- that\'s about 66 times faster than typical DSL. FTTCis cost-prohibitive in many cases. Installing FTTH can be expensive, and the monthly charge for broadband services thereafter can also be off-putting, though these figures vary widely. Expense is likely to drop with time as FTTH becomes more common. PART B 1. Explain the following 1.ISDN D channel protocol ii. Hybrid fiber coax systems. 2. Write in detail about ISDN basic rate access architecture.

3. Explain in detail about digital satellite service. 4. Explain the function of digital loop carrier systems.. 5. Explain in detail about ADSL with suitable block diagram. 6. Explain the concept of down stream V.90 modem. 7. Explain the following i. Local microwave distribution service ii. Fiber in the loop. 8. Enumerate the ISDN basic rate access architecture with a neat diagram. 9. Give a brief account on the different services supported by ISDN. 10. Describe the digital loop carrier systems with neat diagrams. 11. Write a brief note on fiber in the loop. 12. Explain the techniques used in high data rate digital subscriber loops. 13. Discuss the principles of digital loop carrier systems. 14. Write short notes on; i. Hybrid fiber coax systems ii. PCM modems iii. ISDN B and D channels.

UNIT 5 TRAFFIC ANALYSIS PART A 1. Define an Erlang. Traffic intensity is usually expressed in terms of Erlang. 2. Define traffic intensity. Traffic intensity is obtained by dividing the traffic volume by the length of time during which it is measured. Thus the traffic intensity represents the average activity during a period of time. 3. Define Busy hour. The maximum capacity of a single server is defined as one erlang, which is said to be busy hour. 4. What is loss system?

The long term average of offered traffic is less than the capacity of the network. A delay system carries all carried traffic. If the number of requests that can be waiting for service is limited. A delay system also takes on properties of a loss system. 5. What is TASI? System that closely fits the lost calls held model is time assignment speech interpolation (TASI). A TASI system concentrates some number of voice sources onto a number of transmission channels. In modern counter parts of TASI rae referred to as digital circuit multiplication systems. 6. What is delay system? The Tele traffic analysis concerns systems that delay nonserviceable requests until the necessary facilities become available.. these systems are variously ref as the delay systems. 7. What is blocking probability? The arrival rate when N servers are busy is (M-N)/M times the arrival rate when no servers are busy, then the blocking probability is determined for lost calls cleared with a finite source. 8. Draw the queuing system notation of a delay system. 9. What are the two categories used to analyze the traffic? Arrival distributions Holding time distributions Network blocking probabilities

10. Distinguish call congestion and time congestion. Time congestion is a percentage of time that all servers in a group are busy Time congestion and Call congestion are identical because the percentage of arrivals encountering all servers busy is exactly equal to the time congestion. In a finite source system, call congestion is always less than the time congestion. 11. What is packet switched node? When the ATM packet is an intermediate node, the IP packet is passed back down through a AAL5 interface to get back into the ATM network. 12. Define call congestion. Call congestion are identical because the percentage of arrivals encountering all servers busy is exactly equal to the time congestion. PART B

1. Discuss about loss system. 2. Explain in details about Delay systems. 3. Explain the following traffic characterizations i. Arrival distribution ii. Holding time distribution. 4. Short notes on following i. End to end blocking probalities ii. Lost call cleared systems. 5. Discuss about the last call cleared system & lost calls returning system in switching system. 6. Describe the effect of blocking probability on the network traffic. 7. What is probability that a talk spurt experience clipping in a TASI system with 10 sources & 5 channels? Assume activity factor of each talker is 0.4. 8. Explain the LCC systems with infinite sources and derive the Erlang B formula. What happens when the sources become finite? 9. A rural telephone exchange normally experiences four call origination per minute. What is the probability that exactly seven calls occur in an arbitrarily chosen interval of 20 seconds? 10. Compare LCH and LCR systems. 11. Discuss the applications of delay systems in modeling and analyzing communication networks. 12. Discuss LCC systems with infinite and finite sources. 13. A TASI system has 10 channels and 20 sources connected to it. What is the probability of clipping if the activity factor for each source is 0.4? 14. Explain the arrival and service time distributions used in telecommunication traffic analysis. 15. A PCO is installed in a busy part of a town. 150 persons use the booth everyday.Average holding time for a call is 1.5 mm. Find the probability of delay and average waiting time. Assume a single server queue.