Introduction

1. MOBILE COMPUTING
INTRODUCTION
S J Savitha
Assistant Professor
Computer Science and Engineering
Sri Ramakrishna Institute of technology
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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
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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.
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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.
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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
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6. MOBILE COMMUNICATION:
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 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.
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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.
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9. MOBILE COMPUTING DEVICES
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Modem
Laptop
Palm-
top
GPS
Mobile
phone

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
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11. TYPES OF COMMUNICATION NETWORKS
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12. LAN (LOCAL AREA NETWORK)
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13. MAN (METROPOLITAN AREA
NETWORK)
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14. WAN(WIDE AREA NETWORK)
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15. INTERNETWORK
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16. WIRELESS NETWORK
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17. MOBILE COMPUTING
UNIT 1
MOBILE COMPUTING VS
WIRELESS NETWORKING
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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.
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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.
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20. CHARACTERISTICS OF WIRELESS NETWORKS
 Mobility
 Reachability
 Simplicity
 Maintainability
 Roaming Services
 New Services
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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.
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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.
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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.
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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).
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25. MOBILE COMPUTING APPLICATIONS
 Emergency services
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26. 26

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.
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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.
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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)
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40. 40

41. 41

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.
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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.
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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.
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45. MAC PROTOCOLS
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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.
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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.
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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.
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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.
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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.
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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.
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52.  Exposed 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.
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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.
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54. FIXED ASSIGNMENT SCHEMES :
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Fixed Assignment
schemas
FDMA (Frequency
Division Multiple Access)
CDMA(Code Division Multiple
Access)
TDMA (Time Division
Multiple Access)

55. FDMA :
o In FDMA, the available bandwidth is divided into
many narrower frequency bands called channels.
o 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.
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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
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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
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58. 58

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