Northern India Engineering College, New Delhi Question Bank Mobile Computing (ETEC 407) B. Tech. Computer Science & Engineering VII Semester

Transcription

1 Q1. Differentiate between signal and data. The term data represents message or information where the signal is the representation of the data, and it is also termed as information bearing signal. Q2. What is a periodic signal? In a signal if a particular signal pattern repeats over a time period systematically it is a periodic signal. Q3. What is a Aperiodic signal? In a signal if the same signal pattern does not repeat itself over a time period it is known as Aperiodic signal. Q4. Give an example for periodic and aperiodic signals. a. periodic signal x (t + T) = x(t). where - < t < + b. Aperiodic signal x (t + T) x(t). Q5. Define wavelength. The wavelength of a signal represents its distance or range it takes for one cycle. It is denoted as λ. Wavelength λ = c/f Q6. What is a bandwidth? Bandwidth is the range of frequencies and represented as BW = f 2 f 1, where f 1 f 2 are the first and last frequencies of the signal graph. Q7. Define attenuation. It is nothing but reduction in signal strength mainly at higher frequency ranges, and at receiving end this attenuated signal has reduced voltage levels. Q8. Draw the diagram of multiplexing. M D U One link E Input X M Outputs U X 1 Saurabh Gupta, AP - CSE

2 Q9. What is the principle used in multiplexers? The principle used in multiplexer is many to one concept. Many inputs are combined as one link or one output from a MUX unit where a DEMUX unit at the receiver reproduces the same many units at the end entity. Q10. What are the important multiplexing schemes? Multiplexing Frequency Division Time Division Code Division Multiplexing (FDM) Multiplexing (TDM) Multiplexing (CDM) Q11. What are the multiple access schemes? a) FDMA b) TDMA c) CDMA Q12. What is personal communication? Ans The vision for the emerging mobile and personal communication services and system is to enable communication with a person, at any time, at any place, and in any form. Besides providing unlimited reach ability and accessibility, this vision for personal communication is also underlines the increasing need for users of communication services to be able to manage their individual calls, and services according to their real time needs. Q13. What are the different kinds of mobility? Terminal mobility: Terminal mobility systems are characterized by their ability to locate and identify mobile terminals as it moves, and to allow the mobile terminal to access telecommunication services from any location-even while it is in motion. Terminal mobility is associated with wireless access and requires that the user carry a wireless terminal and be with in a radio coverage area. Personal mobility: personal mobility on the other hand, relies on a dynamic association between the terminal and the user, so that the call delivery and billing can be based on a personal identity assigned to a user. Personal mobility systems are therefore characterize by their ability to identify 2 Saurabh Gupta, AP - CSE

3 end users as they move, and allow end users to originate and receive calls, and to access subscribed telecommunication services on any terminal, in any location. Service portability: it refers to the capability of a network to provide subscribed services at the terminal or location designated by the user. The exact services the user can invoke at the designated terminal, of course, depend on the capability of the terminal and the network serving the terminal. Q14. Define guard band. It is unused (dummy) frequency inserted with actual spectrum to reduce adjacent channel interference to enhance accuracy. Q15. What are the types of spread spectrum and differentiate them? a) FHSS - Frequency Hopping Spread Spectrum b) DSSS Direct Sequence Spread Spectrum.. DSSS Each bit in transmission can be represented as multiple bits. FHSS Signal is transmitted in random series at fixed time intervals. Synchronization between transmitter and receiver is a must. Q16. Define a cell. The smallest geographical area covered by wireless communication is said to be a cell. Q17. What are the shapes related to a cell? In early days three shapes namely. a. Circle b. Square c. Hexagon were suggested for a cell. But coverage of signal was very accurate with hexagonal shaped cells and in later stage it was taken as standard. Q18. Define BTS. BTS is the base transceiver station available in each cellular region. 3 Saurabh Gupta, AP - CSE

4 Q19. What is a MSC? What are the functions of MSC in network and switching subsystem? It is mobile switching center and it enables connectivity between BTS and PSTN. (i) It is like a normal switching node for PSTN fixed telephone and for cellular subscribers of the same network. (ii) It is possible to have functions like registration, location updating, and authentication, call routing etc. Q20.What is known as handoff'? Handoff is a principle used to continue the call established in mobile communication. When the subscriber is towards the cell boundary the signal strength reduces by which the BTS of that cell hand over the call to the next BTS of another cell where the subscriber enters. Q21. What are the types of handoff? a) Hard hand off. b) Soft handoff. Q22. What is mobility management? Mobility management is one of the major functions of a GSM or a UMTS network that allows mobile phones to work. The aim of mobility management is to track where the subscribers are, allowing calls, SMS and other mobile phone services to be delivered to them. Q 23.What is frequency reuse in cellular systems? The key characteristic of a cellular network is the ability to re-use frequencies to increase both coverage and capacity. As described above, adjacent cells must utilize different frequencies, however there is no problem with two cells sufficiently far apart operating on the same frequency. The elements that determine frequency reuse are the reuse distance and the reuse factor. The reuse distance, D is calculated as where R is the cell radius and N is the number of cells per cluster. Cells may vary in radius in the ranges (1 km to 30 km). The boundaries of the cells can also overlap between adjacent cells and large cells can be divided into smaller cells. The frequency reuse factor is the rate at which the same frequency can be used in the network. It is 1/K (or K according to some books) where K is the number of cells which cannot use the same frequencies for transmission. Common values for the frequency reuse factor are 1/3, 1/4, 1/7, 1/9 and 1/12 (or 3, 4, 7, 9 and 12 depending on notation). 4 Saurabh Gupta, AP - CSE

5 In case of N sector antennas on the same base station site, each with different direction, the base station site can serve N different sectors. N is typically 3. A reuse pattern of N/K denotes a further division in frequency among N sector antennas per site. Some current and historical reuse patterns are 3/7 (North American AMPS), 6/4 (Motorola NAMPS), and 3/4 (GSM). If the total available bandwidth is B, each cell can only utilize a number of frequency channels corresponding to a bandwidth of B/K, and each sector can use a bandwidth of B/NK. Cells with the same number have the same set of frequencies. Here, because the number of available frequencies is 7, so the frequency reuse factor is 1/7. That is each cell is using 1/7 of available cellular channels. Q 24. What is cluster? A cluster is a group of cells. No channels are reused with in a cluster. Figure shows 7-cell cluster. 5 Saurabh Gupta, AP - CSE

6 Q25. List all the services provided by GSM. a) Tele services. b) Bearer services. c) Supplementary services. Q26. What are the services provided by supplementary services? User identification Call redirection Call forwarding Closed user groups Multiparty Communication Q27. What are the different managements under GSM protocol architecture? (i) Mobility management (ii) Connection management (iii) Radio resource management (iv) Message transfer Q28. What is a TCH/H GSM channel? It is half rate traffic channel that supports traffic channels with half-rate speech coding. It can use up to 16 slots in one frame with a data rate of 11.4 kbps/sec. Q29. What are the common control channels? The common control channels (CCCH) are used for call establishment and they are basically one way channels. 6 Saurabh Gupta, AP - CSE

7 Q30. What are types of CCCH? (i) Random access channel (RCH) (ii) Paging channel (PCH) (iii) Access grant channel (AGCH) Q31. What is a RCH? For establishing a call RCH (Random access channel) is used by mobile station to access the base station involved. Q32. What is DCCH? What are the types of DCCH? It is duplicated control channels known as two way channels and it is useful for signaling and control operations for individual subscribers. DCCH types: (i) Stand alone dedicated control channel (SDCCH) (ii) The slow associated control channel (SACCH) (iii) The fast associated control channel (FACCH) Q33. What are the four types of handover available in GSM? (i) Intra cell Handover (ii) Inter cell Intra BSC Handover (iii) Inter BSC Intra MSC handover (iv)inter MSC Handover Q34. What are subsystems in GSM system? Radio subsystem(rss) Network & Switching subsystem(nss) Operation subsystem(oss) Q35.What are the information in SIM? card type, serial no, list of subscribed services Personal Identity Number(PIN) Pin Unlocking Key(PUK) An Authentication Key(KI) Q36. What is meant by GPRS? The General Packet Radio Service provides packet mode transfer for applications that exhibit traffic patterns such as frequent transmission of small volumes. Q37. What is the function of an AuC? The authentication center (AuC) maintains copy of secret key that is stored in each and every subscribers SIM card. It is used to protect user s database. 7 Saurabh Gupta, AP - CSE

8 Q38. What are the three types of switching methods? a. Circuit switching b. Message switching c. Packet switching Q39. What is QoS in GPRS. In GPRS the users can specify the QoS profile where the profile determines important things like reliability class, delay class and service precedence. Q40. What is the use of SS7? (a) In network subsystem the SS7 (signaling system number 7) is used for signaling between different functional entities. (b) SS7 is used for SMS, roaming prepaid network functions. (c) SS7 is also used for trunk signaling. Q41. What are the parameters considered for defining QoS in GPRS technology? (i) Service precedence (ii) Delay (iii) Throughput (iv) Reliability Q42. A certain city has an area of 1300 square miles and is covered by a cellular system using a seven cell reuse pattern. Each cell has a radius of 4 miles and the city has 40 MHz spectrum with a full duplex channel bandwidth of 60KHz. Find: (i) The number of cells in the service area. (ii) The number of channels per cell. (iii) Total number of subscribers that can be served. (i) Radius of a cell = 4 miles Area covered by cell = 50 square miles. For 7 cell reuse pattern Area covered by cluster = 7*50 = 350 square miles. So, no. of cells required to cover 1300 square miles is 28. (ii)no. of channels per cell = total no. of channels/no. of cells in a cluster Available frequency = 40MHz Channel bandwidth = 60 KHz No. of channels available = 40 MHz/60KHz = 666 channels No. of channels per cell = 666/7= 95 channels per cell. (iii)total number of subscriber that can be served =666*4 = 2664 subscribers. Q43. If a total of 33 MHz of bandwidth is allocated to a particular cellular system which uses two 25 KHz Simplex channels to provide full Duplex voice. Compute the number of channels available per cell if the system uses: (i) 4 cell reuse (ii) 7 cell reuse 8 Saurabh Gupta, AP - CSE

9 Available bandwidth = 33 MHz Channel bandwidth = 25 KHz Total no. of channels available = 1320 simplex channels. (i) (ii) For 4 cell reuse No. of channels per cell = 1320/4 = 330 channels For 7 cell reuse No. of channels per cell = 1320/7 = 188 channels Q44. What are the functions of MSC in network and switching subsystem? (i) It is like a normal switching node for PSTN fixed telephone and for cellular subscribers of the same network. (ii)it is possible to have functions like registration, location updating, and authentication, call routing etc. Q45. State the requirements of mobile IP. i. Compatibility ii. Transparency iii. Scalability and efficiency iv Security Q46. What is COA? How is it assigned? Care-or address (COA): The COA defines the current location of the MN from an IP point of view. There are two different possibilities for the location of the COA: Foreign agent COA Co-located COA Q47. How does a MN identify that it has moved? Mobile IP describes two methods: agent advertisement and agent solicitation, which are in fact router discovery methods plus extensions. Q48. What are the contents of mobility binding? Mobility binding containing the mobile node s home IP address and the current COA. Additionally, the mobility binding contains the lifetime of the registration which is negotiated during the registration process. Q49. Define encapsulation. List the types of encapsulation. Encapsulation is the mechanism of taking a packet consisting of packet header and data and putting it into the data part of new packet. The reverse operation, taking a packet out of the data part of another packet, is called decapsulation. IP-in-IP encapsulation 9 Saurabh Gupta, AP - CSE

10 Minimal encapsulation Generic routing encapsulation Q50. State any 4 features of IPv6. No special mechanisms as add-ons are needed for securing mobile IP registration. Every IPv6 node masters address auto configuration the mechanisms for acquiring a COA are already built in. Neighbor discovery as a mechanism mandatory for every node is also included in the specification; special foreign agents are no longer needed to advertise services. Combining the features of auto configuration and neighbor discovery means that every mobile node is able to crate or obtain a topologically correct address for the current point of attachment. Every IPv6 node can send binding updates to another node, so the MN can send its current COA directly to the CN and HA. Q51. State the layers in WAP architecture. Transport layer Security layer Transaction layer Session layer Application layer Q52. What are the different security levels offered by WTLS? (i) Privacy (ii) data integrity (iii) authentication Q53. How is reliability achieved in WTP? (i) duplicate removed (iii) acknowledgements Q54. What are the functions of WSP? (i) session management (iii)content encoding Q55. List any 4 basic features of WML. (i) Text and images representation. (ii) Navigation (ii) retransmission (iv) unique transaction identifier. (ii) Capability negotiation (ii) User interaction (iv) Context management. 10 Saurabh Gupta, AP - CSE

11 Q56. List any 4 capabilities of WML script. (i) Validity check of user input (iii) Local user interaction (ii) Access to device facilities (iv) Extension to the device software. Q57. What are the benefits of IMT-2000 over 2G systems? (i) Circuit and packet bearer capability up to 144 kbps. (ii) User authentication and ciphering. (iii) Multimedia services. (iv) Emergency and priority calls. Q58. Compare MEO and LEO satellite types. Characteristics MEO LEO Satellite lifetime 10 to 15 years 4 to 8 years Altitude range 10,000 to km 500 to 2000 km Round - trip delay 40 to 80 msec 5 to 10 msec Q59. What is a GEO? The communication satellite (GEO) orbits in geo stationary orbit which is at km above earth's surface. The satellite revolves with same speed as that of the earth (1 Rev / day) that revolves around sun. Q60. What are examples of global mobile satellite system? (i) Iridium (ii) Teledesic (iii) Global star Q61. Give three specifications of Global star and Iridium systems. Characteristic Global star Iridium System type LEO LEO Data speed 7.2 kbps 2.4 kbps Launched year Saurabh Gupta, AP - CSE

12 Q62. What are the advantages of Iridium satellite system? (i) Inter-satellite links are possible. (ii) Number of satellites possible is 66 and 6 numbers of satellites can be maintained as spares. (iii) The terminal types can be of dual mode, mobile or handheld. Q63. Give few advantages of GEO satellites. (i) They have large footprints and provide large coverage. (ii)used for communication related applications. Q64. What is the demerit of GEO satellite? Their round trip time delay is long due to high altitudes, and it results in qua1ity degradation. Q65. What are the advantages of LEO satellites? (i) LEO satellites provide higher global coverage. (ii) High spectrum utilization. (iii)the propagation delay is lower (say 5 to 10 msec). Q66. What are the demerits of LEO system? (i) The network architecture is complex. tough. (iii) Routing mechanism is difficult. (ii) Satellite movement is rapid and analysis is (iv) Long period of deployment. Q67. What is IEEE ? Explain 802.ii family. IEEE is a set of standards for implementing wireless local area network (WLAN) computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee (IEEE 802). IEEE Family protocol Freq. (GHz) Bandwidth (MHz) Data rate per stream (Mbit/s) Allowable MIMO streams Modulation ,2 1 DSSS,FHSS 12 Saurabh Gupta, AP - CSE

13 a ,9,12,18,24,36,48,54 1 OFDM b ,11 1 DSSS g ,9,12,18,24,36,48,54 1 OFDM,DSSS n 2.4/5 20/40 7.2, 14.4, 21.7, 28.9, 43.3, 57.8, 65, 72.2/ 15, 30, 45, 60, 90, 120, 135, OFDM Q68. What is WLL? Draw the WLL setup diagram. WLL is a system that connects subscribers to the local telephone station wirelessly. It is based on: Cellular Satellite (specific and adjunct) Microcellular Its Other names: Radio In The Loop (RITL) Fixed-Radio Access (FRA). A general WLL Setup 13 Saurabh Gupta, AP - CSE

14 Q69. State the modes possible when the slave is in connection state in Bluetooth. (i) Active (ii) Sniff (iii) Hold (iv) Park Q70. What are elements available under link security of Bluetooth technology? (i) Authentication (ii) Key management (iii) Encryption Q71. What is a LMP? List three security services under LMP. It is link manager specification that is responsible for radio link between the master and slave in Bluetooth. This protocol also involves message exchanges in the form of LMP-PDU s. a) Authentication b) Change link key c) Encryption Q72. What is Bluetooth? List few functions of Bluetooth. It is a low power short range wireless standard and it can operate in situations where several users are involved. At the maximum eight different devices can communicate in a network using this standard. (i) It can make call from a headset (wireless) to a mobile phone which is at a distant place. (ii) It can trigger MP3 players on some other machines to download audio signals like music in wireless environment. (iv) It mainly eliminates cables in many user applications. Q73. Differentiate piconet and scatternet in Bluetooth technology. (i) Piconet It is a basic network supported by Bluetooth standard where one master and seven slaves (total eight devices) can interact. (ii) Scatternet A device in one piconet either a master or slave can interact with other device that is overlapping of one piconet on other piconet is possible and termed as a Scatternet. Q74. What is an IrDA standard? IrDA is a standard that is specified by Infrared Data Association formed in the year It was developed mainly to enhanced point-to-point or point-to-multipoint communication. It is dependant on line of sight (LOS) operation. The infrared rays can be used wherever LOS is preferred and useful for this indoor consumer applications. Q75. What are the specifications of IrDA? The IrDA standard 1.0 supports the data rate up to kb/sec. for the range up to 1m and next version IrDA 1.1 developed later supports data transfers up to 35 times faster when compared to IrDA Saurabh Gupta, AP - CSE

15 Q76. What are the new specifications supported by current Bluetooth? The short range Bluetooth technology is improved for meeting the distance of 100m in open air and 30 m within building infrastructures for it s operation. It works with data rate of 1 Kbps. Q77. What re the two kinds of profiles in Bluetooth 1.1 version? The two main profile classification is nine application profiles and four system profile and as a whole thirteen profiles are supported by Bluetooth 1.1 version. Q78. What are the system profiles used in Bluetooth 1.1 version? The system profiles are generic object exchange, object push, file transfer and synchronization profiles. 15 Saurabh Gupta, AP - CSE