Mobile computing

Introduction

1. MOBILE COMPUTING INTRODUCTION S J Savitha Assistant Professor Computer Science and Engineering Sri Ramakrishna Institute of technology 1

2. What Is Mobile Computing? What is computing? Operation of computers (according to oxfords advance learner’s dictionary ) What is the mobile? That someone /something can move or be moved easily and quickly from place to place What is mobile computing? Users with portable computers still have network connections while they move 2

3. Mobility provides the capability to change location while computing goes on. Computing denotes the capability to carry out processing automatically related to service provided to the user. 3 MOBILE COMPUTING = MOBILITY + COMPUTING

4. A simple definition could be: Mobile Computing is using a computer (of one kind or another) while on the move Another definition could be: Mobile Computing is when a (work) process is moved from a normal fixed position to a more dynamic position. A third definition could be: Mobile Computing is when a work process is carried out somewhere where it was not previously possible. 4

5. Mobile Computing involves the invocation of applications running on remote servers. Mobile Computation The main concept involves in Mobile Computing : 1.Mobile Communication 2.Mobile Software 3.Mobile Hardware 5

6. Mobile Communication: 6 Mobile communication refers to the infrastructure put in place to ensure that reliable communications goes on without any collision with other existing systems.

7. Mobile Software Mobile software is the actual program that runs on the mobile hardware. It deals with the characteristics and requirements of mobile applications. 7

8. Mobile Hardware Mobile hardware includes mobile devices or device components that receive or access the service of mobility. These devices are configured to operate in full- duplex, whereby they are capable of sending and receiving signals at the same time. 8

9. Mobile computing devices 9

10. Telecommunication Networks A Telecommunication networks is an arrangement of computing and telecommunication resources for communication of information between distant locations. Components : 1. Terminals 2.Computers 3.Telecommunication links 4.Telecommunication equipment 5.Telecommunication Software 10

11. Types of Communication Networks 11

12. LAN (LOCAL AREA NETWORK) 12

13. MAN (METROPOLITAN AREA NETWORK) 13

14. WAN(WIDE AREA NETWORK) 14

15. INTERNETWORK 15

16. WIRELESS NETWORK 16

17. MOBILE COMPUTING UNIT 1 mobile computing vs wireless networking 17

18. wireless networking A wireless network is any type of  computer network  that uses wireless data connections for connecting   network nodes. Wireless  means transmitting signals using radio waves as the medium instead of wires. 18

19.  Wireless technologies are used for tasks as simple as switching off the television or as complex as supplying the sales force with information from an automated enterprise application while in the field. 19

20. Characteristics of wireless networks Mobility   Reachability   Simplicity Maintainability   Roaming Services   New Services   20

21. Mobile computing vs wireless networking Two terms are not synonymous. Mobile computing essentially denotes accessing information and remote computational services while on the move. Wireless networking provides the basic communication infrastructure necessary to make this possible. Thus mobile computing is based on the wireless networking and helps to invoke the computing services on remote servers. 21

22. Instead of studying the different aspects of mobile computing applications, designs and development, we need to have a good knowledge of the basics of wireless communication technologies. Wireless networks are increasingly replacing the traditional networks. Wireless network can be classified into two basic types : 1. Extension of wired networks. 2. Ad hoc networks. 22

23. The extension of wired networks uses the fixed infrastructures such as base stations to provide essentially single hop wireless communication with a wired networks. Example : Wireless LAN(WLAN) that implements the IEEE 802.11 protocol. 23

24. An Ad hoc network does not use any fixed infrastructure and is based on multi-hop wireless communication. An ad hoc network is also called as a Mobile Ad hoc Network(MANET). 24

25. Mobile computing Applications Emergency services 25

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27. Useful to Executives

28. Credit card verification

29. For Legal Purposes

30. For Estate Agents

31. Taxi/Truck Dispatch

32. Electronic Mail/Paging

33. VEHICLES Transmission of news, road condition

34. TRAVELLING SALESMEN Direct access to central customer files consistent databases for all agents mobile office

35. WEB ACCESS Outdoor internet access

36. ENTERTAINMENT Ad-hoc networks for multi user games,movies,music

37. CHARACTERISTIC OF MOBILE COMPUTING Ubiquity It means –any time every where. This characteristic make the user to compute at anytime he needs and can compute anywhere he goes. Location Awareness A mobile devices with global positioning system can transparently provide information about the current location of a user to a tracking station. Adaption Adaption is the ability of the mobile devices to adjust to bandwidth fluctuation without distributing the user. 37

38. Broadcast Due to the broadcast nature of mobile computing, efficient delivery of data can be made simultaneously to the hundreds of user . Personalization Services in mobile environment can be easily personalized according to a user’s profile. This is required to let the users easily avail information with their handheld devices. 38

39. Structure of mobile computing application A mobile computing application is usually structured in terms of the functionalities implemented. The structure of mobile computing can be implement with three tiers. The three basic layers are 1.Presentation layer(Tier-1) 2.Application layer(Tier-2) 3.Data layer(Tier-3) 39

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42. Presentation Tier The topmost level of a mobile computing application concerns the user interface. A good user interface facilitates the users to issue requests and to present the results to the them meaningfully. The computing codes of this layer usually runs on the client’s computer including web browsers and client programs to give information to the user and also to collect data from the user. 42

43. Application layer The application layer makes logical decisions and perform calculations according to the user’s query. It also moves and processes data between the presentation and data layers. This application layer is implemented using technology like java, .NET services etc., This layer is database independent and all these functionalities are implemented on a fixed server. 43

44. Data Layer Data layer provides the basic functions with data like storing data, retrieve data and manipulating data. Data layer has a database and all the information is stored and retrieved from the database. This layer is also implemented on a fixed layer. 44

45. MAC PROTOCOLS 45

46. Medium Access Control(MAC) The MAC protocol is a sublayer of the data link layer protocol and it directly invokes the physical layer protocol. The MAC layer emulates a full-duplex logical communication channel in a multi-point network. This channel may provide unicast, multicast or broadcast communication service . The MAC sublayer provides addressing and channel access control mechanisms that make it possible for several terminals or network nodes to communicate within a multiple access network that incorporates a shared medium. 46

47. The primary responsibility of a MAC protocol is to enforce discipline in the access of a shared channel when multiple nodes contend to access that channel. MAC protocol must ensure that no node has to wait for a long time, before it is allowed to transmit. The two objectives of MAC protocol are : 1.Maximization of the utilization of channel 2.Minimization of average latency of transmission. 47

48. Properties of Mac protocol It should implement some rules that help to maintain discipline when multiple nodes contend for a channel. It should help maximize the utilization of the channel. Channel allocation need to be fair. It should be capable of supporting several types of traffic having different maximum and average bit rates. It should be robust. 48

49. At present, IEEE 802.11 has emerged as a popular and standard MAC protocol for wireless networks. Wireless networks can be classified into two categories : 1.Infrastructure-based wireless networks (WLAN) 2.Infrastructure-less wireless networks.(MANET) The MAC protocols for the above two environments have many things in common, MAC protocols for infrastructure –less networks are much more complex. 49

50. Wireless MAC protocols : Issues HIDDEN and EXPOSED Terminal problem In Infrastructure-less networks , the issue of hidden and exposed terminals make a MAC Protocol extremely inefficient. The hidden terminal problem arises when at least three nodes (Ex : A, B, C) communicates among each other. 50 Hidden terminal problem

51. B is in the radio range of A and also in the radio range of C. However, the nodes A and C are not in the range of each other. If both A and C start to transmit a data to B at the same time, the data received at node B would get garbled. Such a situation arises because A and C are “hidden” from each other. In this situation, when one node starts to sense the medium before transmission, it cannot sense that the other node is also transmitting. This creates a very difficult and important arbitration problem. 51

52. E xposed Terminal problem : In exposed terminal problem, MAC protocols usually inhibit transmission when transmission from another terminal is detected. A node will not be able to transmit data to any node when B is transmitting to C. The problem occurs because A is exposed to B’s transmission. 52 Exposed terminal problem

53. Taxonomy of MAC protocols A large number of MAC protocols have been proposed. These MAC protocols can be broadly divided into three categories: 1.Fixed Assignment schemes 2.Random Assignment schemes 3.Reservation-based Schemes The Fixed assignment schemes are called as circuit-switched schemes. The random assignment and reservation based schemes are called as packet-switched schemes. 53

54. Fixed assignment schemes : 54 Fixed Assignment schemas FDMA (Frequency Division Multiple Access) CDMA(Code Division Multiple Access) TDMA (Time Division Multiple Access)

55. FDMA : In FDMA, the available bandwidth is divided into many narrower frequency bands called channels. Each user is allocated a forward link(channel) for communicating from it(mobile handset) to base station A reverse channel for communicating from the BS to it. 55

56. Two unique frequency –transmitting and receiving signal No other user would be allocated the same frequency band to make a call Unused transmission or when no user is allocated a band it goes to idle or waste FDMA does not achieve high channel utilization 56

57. TDMA Multiple nodes are allocated different time slots to access the same physical channel Timeline is divided into fixed sized time slots and these are divided among multiple nodes who can transmit All sources use the same channel but take turns in transmitting Round robin method is been used with each user being assigned one time slot per frame Unused time slots go idle leading low channel utilization 57

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59. CDMA Multiple users are allocated different codes that consists of sequence of 0 and 1 to access the same channel. Different users who have assigned separate codes are multiplexed on the same physical channel. A code for a user should be orthogonal to the code assigned to other codes. Bandwidth >space allocated to each transmission. 59

60. Random Assignment Schemes Connectionless Packet Switched Scheme. No resource reservation are made. The node transmit as soon as they have a packet to send. CATEGORIES 1.ALOHA 2. Slotted ALOHA 3.CSMA 4.CSMA/CD 5.CSMA/CA 60

61. Aloha scheme Simple communication scheme The basic ALOHA Scheme is called as Pure ALOHA ( simple protocol). If a node has data to send it begins to transmit. Does not check whether the channel is busy before transmitting. If the frame is successfully reaches the next frame is sent, if it fails it has to be resent. It works only when small amount of sender data is sent. Collision occurs when transmission is high. 61

62. Improvement over pure ALOHA is slotted ALOHA. Slotted ALOHA Time is divided into equal time slots in which packets are sent. By this packet size is restricted Only at the beginning of a slot packet can be sent Beacon signals for transmitting the data if the number of contending to send data is high, this protocol does not work 62

63. CSMA Scheme Popular MAC attribution technique. A node senses the medium before starting to transmit. Two popular extensions are 1. CSMA/CD 2. CSMA/CA CSMA/CD If it sense the channel to be free and transmit the data still collision occurs Received signal from other nodes would be too weak compared to its own signal and can be masked by noise. 63

64. Destination node will have corrupted frame after it computes . But in wired network when a node is detected with collision it immediately stops transmitting Minimizing channel wastage. 64

65. CSMA/CA Avoidance scheme works better compared to collision detection in wireless. When it is released after a packet transmission Not only one node but several nodes might be wanting to transmit. These nodes be monitoring the channel and waiting it to be free. To reduce the transmission of nodes at a time, the node is set to wait for random time and sense the medium again before transmission. 65

66. Reservation based schemes RTS/CTS is the basic form of reservation scheme.(RTS –Ready To Send , CTS –Clear To Send) Sender transmits an RTS packet to the receiver before the actual data transmission. Receiver sends a CTS packet, and the actual data transfer commences after that. Examples: MACA,MACAW,MACA–BI ,PAMAS,DBTMA, MARCH,S-MAC. 66

67. MACA MACA- Multiple Access Collision Avoidance. It solves the hidden/exposed terminal by transmitter power. With MACA, A does not start its transmission at once, but sends a request to send ( RTS) first . 67

68. 68 B receives the RTS that contains the name of sender and receiver, as well as the length of the future transmission. This RTS is not heard by C, but triggers an acknowledgement from B, called clear to send (CTS). The CTS again contains the names of sender (A) and receiver (B) of the user data, and the length of the future transmission . This CTS is now heard by C and the medium for future use by A is now reserved for the duration of the transmission.

69. After receiving a CTS, C is not allowed to send anything for the duration indicated in the CTS toward B. A collision cannot occur at B during data transmission, and the hidden terminal problem is solved. Still collisions might occur when A and C transmits a RTS at the same time. B resolves this contention and acknowledges only one station in the CTS. No transmission is allowed without an appropriate CTS. 69

70. Now MACA tries to avoid the exposed terminals in the following way : With MACA, B has to transmit an RTS first containing the name of the receiver (A) and the sender(B). C does not react to this message as it is not the receiver, but A acknowledges using a CTS which identifies B as the sender and A as the receiver of the following data transmission . 70

71. C does not receive this CTS and concludes that A is outside the detection range. C can start its transmission assuming it will not cause a collision at A. The problem with exposed terminals is solved without fixed access patterns or a base station. 71

72. END………………… 72