Mobile computing

Introduction: Mobile Communications, Mobile Computing – Paradigm, Promises/Novel Applications and Impediments and Architecture; Mobile and Handheld Devices, Limitations of Mobile and Handheld Devices.
GSM – Services, System Architecture, Radio Interfaces, Protocols, Localization, Calling, Handover, Security, New Data Services, GPRS, CSHSD, DECT.

1. MOBILE COMPUTING
LECTURE NOTES
III-CSE
PRESENTED BY :
Dr R JEGADEESAN, Professor and
Head,Departmentof Computer Science and
Engineering

2. UNIT –I CONTENTS
▪MobileCommunication
▪MobileComputing
▪NovelApplications
▪Location dependentservices
▪Effects of deviceportability
▪Wireless n/w‘sin comparison with fixedn/w‘s
▪Limitations
▪Architecture (simple referencemodel)

3. 3
Goal of MobileComputing
➢Peopleandtheirmachinesshouldbeableto
accessinformationandcommunicatewith
eachothereasilyandsecurely,inanymedium
orcombinationofmedia
–voice, data, image, video, or multimedia any
time, anywhere, in a timely, cost-effectiveway.

4. 4
MobileComputing
•Mobilecomputingreferstocomputinginadistributed
systeminwhichsomeprocessesorprocessorscan
move.
–Moving processes logical mobility, realized byagents.
–Movingprocessorsphysicalmobility,realizedbymoving
devices.
•Mobilecomputingextendsadistributedcomputing
environment with a new dimension ofmobility.
–Mostexistingmobilecomputingsystemsarebasedonclient-
server computingsystems.
–Recentmobilecomputingsolutionsconsidergeneraldistributed
computing, namely, peer-to-peer computingenvironments.
•Manymobilecomputingtechniqueshavetheirrootin
distributedsystems.

5. processors
5
Distributedsystem
•Definition:
–Adistributedsystemconsistsofacollectionof
autonomouscomputers,connectedthroughanetwork
anddistributionmiddleware,whichenables
computerstocoordinatetheiractivitiesandtoshare
theresourcesofthesystem,sothatusersperceive
thesystemasasingle,integratedcomputingfacility.
•Multiple autonomouscomponents
•Components are not shared by allusers
•Resources may not beaccessible
•Softwarerunsinconcurrentprocessesondifferent

6. Mobile Computingcontd..,
•The process of computation on a mobiledevice
•Inmobilecomputing,asetofdistributedcomputing
systemsorserviceproviderserversparticipate,connect,
andsynchronizethroughmobilecommunication
protocols
•Mobilecomputingasagenerictermdescribingabilityto
usethetechnologytowirelesslyconnecttoanduse
centrallylocatedinformationand/orapplicationsoftware
throughtheapplicationofsmall,portable,andwireless
computingandcommunicationdevices
6

7. Mobile Computingcontd..,
•Providesdecentralized(distributed)computationson
diversifieddevices,systems,andnetworks,whichare
mobile,synchronized,andinterconnectedviamobile
communication standards andprotocols.
•Mobiledevicedoesnotrestrictitselftojustone
application, such as, voicecommunication
•Offers mobility with computingpower
•Facilitatesalargenumberofapplicationsonasingle
device
7

8. Introduction
MobileCommunication
•UserMobility:
–Referstoauserwhohasaccesstothesameorsimilar
telecommunication services at differentplaces.
–user mobility: users communicate (wireless) ―anytime,anywhere,
withanyone‖
•DevicePortability:
–The communication device moves with or without theuser
–deviceportability:devicescanbeconnectedanytime,anywhere
to thenetwork
•Acommunicationdevicecantheexhibitoneofthe
followingcharacteristics:
–Fixed and wired e.g. Typical desktopscomputer
–Mobile and wired e.g. somelaptops
–Fixed and wireless e.g. WIRELESSLANS
–Mobile and wireless e.g. Mobilephones 8

9. MobilityIssues
•Bandwidth restrictions andvariability
•Location-aware networkoperation
–User may wake up in a newenvironment
–Dynamic replication ofdata
•Querying wireless data & location-basedresponses
•Busty network activity during connections & handling
disconnections
•Disconnection
–OS and File System Issues -allow for disconnectedoperation
–Database System Issues -when disconnected, based onlocal
data
9

10. PortabilityIssues
•Battery powerrestrictions
•Risks todata
-Physical damage, loss,theft
-Unauthorizedaccess
-encrypt data stored onmobiles
-Backup critical data to fixed (reliable)hosts
•Small userinterface
-Small displays due to battery power and aspect ratio
constraints
-Cannot open too manywindows
-Difficult to click on miniatureicons
-Input -Graffiti, (Dictionary-based)Expectation
-Gesture or handwriting recognition with Stylus PenVoice
matching or voicerecognition
10

11. Evolutions of the MobileSystems
1GAnalogsystems
2Gsystems
➢voicecommunication
➢CircuitSwitched
2.5Gsystems
➢Circuit switching forvoice
➢Packet switching fordata
3Gsystems
➢Packet switching for voice anddata
➢Highspeed
➢Compatible with different accesstechnologies
11

12. 5.Gsystems
➢Evolved RadioInterface
➢IP based coreNetwork
➢Compatible with different accesstechnologies
4Gsystems
➢New AirInterface
➢Very High bit rateservices
➢Convergence of Wireline, Wireless, and IPworlds
12
Evolutions of the MobileSystems

13. Evolutions of the MobileSystems
AIRINTERFACE
VOICE
D A TA
2G
(2000)
E A R L Y3 G
(2001)
L A T E3 G
(2003)
4G
(2005)
CIRCUIT CIRCUIT CIRCUIT
CIRCUIT PACKET PACKET
PACKET
ACCESSNETWK
VOICE CIRCUIT CIRCUIT
PACKET PACKET
D A TA CIRCUIT CIRCUIT
C O R EN E T W K
VOICE CIRCUIT
PACKET PACKET PACKET
13
D A TA
OVERLAY
PACKET

14. NovelApplications
14

15. Novel Applications[2]
15

16. Novel Applications[3]
16

17. Location DependentServices
17

18. Effects of DevicePortability
18

19. Wireless Networks in
Comparison with fixednetworks
19

20. Cellular Subscriber(Sept-2008)
20

21. 21
Limitations of the MobileEnvironment
•Limitations of the WirelessNetwork
–heterogeneity of fragmentednetworks
–frequentdisconnections
–limited communicationbandwidth
–Interference: the quality of service(QoS)
–Bandwidth: connectionlatency
•Limitations Imposed byMobility
–lack of mobility awareness bysystem/applications
–routebreakages
–Dynamic changes in communication environment: variations insignal
power within a region, thus link delays and connectionlosses
•Limitations of the MobileComputer
–short batterylifetime
–limitedcapacities

22. Simple ReferenceModel
22

23. Layerfunctionality
23

24. 24
PART-II
Global System forMobile
Communication[GSM]

25. 25
•Introduction
•MobileServices
•GSMArchitecture
•RadioInterface
•Protocols
•Localization andCalling
•Handover
•Security
•New DataServices
CONTENTS

26. 26
Introduction toGSM
GlobalSystemforMobile(GSM)
isasecondgenerationcellular
standarddevelopedtocatervoice
servicesanddatadeliveryusing
digitalmodulation

27. 27
Introduction to GSM[2]
•Developed by Group Special Mobile (founded 1982) which was an
initiative of CEPT ( Conference of European Post and Telecom)
•Aim : to replace the incompatible analogsystem
•Presently the responsibility of GSM standardization resides withspecial
mobile group under ETSI (European telecom Standards Institute)
•GSM have 124 duplex channels, each 200Khz wide, are used forFDMA.
•GSM offer data rates ofupto9.6Kbps and up to a speed of250Km/hr
•Under ETSI, GSM is named as ―Global System for Mobile communication―
•Today many providers all over the world use GSM (more than 190
countries in Asia, Africa, Europe, Australia,America)
•More than 1300 million subscribers in world & 45 million subscriber inIndia.

28. 28
GSMDevelopments
GSM900
Mobile toBTS (uplink):890-915Mhz
BTS to Mobile(downlink):935-960Mhz
GSM 1800 (DCS –Digital Cellular System)
Mobile toBTS (uplink):1710-1785 Mhz
BTS to Mobile(downlink) 1805-1880Mhz
GSM 1900 (PCS –Personal CommunicationService)
Mobile toBTS(uplink):1850-1910Mhz
BTS to Mobile(downlink) 1930-1990Mhz

29. GSM inWorld
Figures: March,2005
ArabWorld
3%
3%(INDIA)
3%
3%
AsiaPacific
Africa
East CentralAsia
4% 37% Europe
Russia
43%
4%
1%
India
NorthAmerica
SouthAmerica
29

30. GSM inIndia
Bharti
27%
BSNL
22%
Spice
4%
IDEA
13%
Hutch
19%
Aircel
4%
BPL
6%
Figures: March2005
Reliance
3%
MTNL
2%
Bharti
BSNL
Hutch
IDEA
BPL
Aircel
Spice
Reliance
MTNL
30

31. 31
MobileServices
•Tele-services
•Bearer or DataServices
•Supplementaryservices

32. 32
TeleServices
•Telecommunication services that enablevoice
communication
via mobilephones
•Offeredservices
-Mobiletelephony
-Emergencycalling

33. 33
BearerServices
•Include various data services for information transfer
between GSM and other networks like PSTN, ISDNetc
at rates from 300 to 9600bps
•Short Message Service(SMS)
–up to 160 character alphanumeric datatransmission
to/from the mobileterminal
•Unified MessagingServices(UMS)
•Group 3fax
•Voicemailbox
•Electronicmail

34. SupplementaryServices
Call related services:
•Call Waiting-Notification of an incoming call while onthe
handset
•Call Hold-Put a caller on hold to take anothercall
•Call Barring-All calls, outgoing calls, or incomingcalls
•Call Forwarding-Calls can be sent to various numbers
definedbytheuser
•Multi Party Call Conferencing -Link multiple callstogether
•CLIP –Caller line identificationpresentation
•CLIR –Caller line identificationrestriction
•CUG –Closed usergroup
34

35. GSM SystemArchitecture
BS
C
BS
C
MSC
MS
MS
MSBT
S
BT
S
BT
S
GMSC
PST
N
ISDN
PDN
EIR
AUC
HLR
VLR
35

36. 36

37. Components
•Mobile Station(MS)
Mobile Equipment (ME)
Subscriber Identity Module(SIM)
•Base Station Subsystem (BSS)
Base Transceiver Station(BTS)
Base Station Controller(BSC)
•Network SwitchingSubsystem(NSS)
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitor Location Register (VLR)
Authentication Center (AUC)
Equipment Identity Register(EIR) 37

38. 38
Mobile Station(MS)
The Mobile Station is made up of twoentities:
1.Mobile Equipment(ME)
2.Subscriber Identity Module(SIM)
MobileEquipment
•Portable, vehicle mounted, hand helddevice
•UniquelyidentifiedbyanIMEI(InternationalMobile
EquipmentIdentity)
•Voice and datatransmission
•Monitoringpowerandsignalqualityofsurrounding
cells for optimumhandover
•Power level : 0.8W –20W
•160characterlongSMS.

39. 39
Subscriber Identity Module(SIM)
•Smart card contains the InternationalMobile
Subscriber Identity(IMSI)
•Allows user to send and receive callsand
receive other subscribedservices
•Encoded network identificationdetails
-Key Ki, Kc and A3,A5 and A8algorithms
•Protected by a password orPIN
•Can be moved from phone to phone –contains
key information to activate thephone

40. Base Station Subsystem(BSS)
BaseStationSubsystem
communicateacross
iscomposedof
thestandardized
twopartsthat
Abisinterface
allowingoperationbetweencomponentsmadebydifferent
suppliers
1.Base Transceiver Station(BTS)
2.Base Station Controller(BSC)
1.Base Transceiver Station(BTS):
•Encodes, encrypts,multiplexes,modulates and feedsthe
RF signals to theantenna.
•Frequencyhopping
•Communicates with Mobile station andBSC
•Consists of Transceivers (TRX)units 40

41. 41
•Manages Radio resources forBTS
•Assigns Frequency and time slots for all MS‘sin
itsarea
•Handles call setup
•Transcoding and rate adaptationfunctionality
•Handover for eachMS
•Radio Powercontrol
•It communicates with MSC andBTS
2. Base Station Controller(BSC)

42. 42
Network SwitchingSubsystem(NSS)
Mobile Switching Center(MSC)
•Heart of thenetwork
•Manages communication between GSM andother
networks
•Call setup function and basicswitching
•Callrouting
•Billing information andcollection
•Mobilitymanagement
-Registration
-LocationUpdating
-Inter BSS and inter MSC callhandoff
•MSC does gateway function while its customer roamsto
other network by usingHLR/VLR.

43. 43
Home Location Registers(HLR)
-permanent database about mobile subscribers in a
large service area(generally one per GSM network
operator)
-database contains IMSI, MSISDN,prepaid/postpaid,
roaming restrictions, supplementaryservices.
Visitor Location Registers(VLR)
-Temporary database which updates whenever newMS
enters its area, by HLRdatabase
-Controls those mobiles roaming in itsarea
-Reduces number of queries toHLR
-Database contains IMSI, TMSI, MSISDN,MSRN,
Location area, authenticationkey

44. 44
Authentication Center(AUC)
-Protects against intruders in airinterface
-Maintains authentication keys and algorithmsand
provides security triplets (RAND,SRES,Kc)
-Generally associated withHLR
Equipment Identity Register(EIR)
-Database that is used to track handsets usingthe
IMEI (International Mobile EquipmentIdentity)
-Made up of three sub-classes: The White List,The
Black List and the GrayList
-Only one EIR perPLMN

45. 45
Radio Interface(Um)
•Air Interface: MS toBTS
•Uplink/Downlink of25MHz
–890 -915 MHz for Uplink
–935 -960 MHz for Downlink
•Combination of frequency division andtime
divisionmultiplexing
–FDMA -124 channels of 200kHz
–TDMA -Burst
•Modulation Method : GMSK (Gaussian
Minimum Shift Keying ) @ 270.833Kbps

46. FDMA/TDMA
46

47. PhysicalChannel
47

48. GSM-FrameStructure
48

49. LogicalChannels
TCH
(traffic)
CCH
(control)
BCH
CCCH
Dedicated
2.4kbps
4.8kbps
9.6kbps
FCCH(Frequencycorrection)
SCH(Synchronization)
PCH(Paging)
RACH(RandomAccess)
AGCH(AccessGrant)
SDCCH(StandAlone)
Half rate11.4kbps
Full rate22.8kbps
Speech
Data
SACCH(Slow-associated)
FACCH(Fast-associated)49

50. 50
BCCH
•BTS toMS
•send cell identities, organization info aboutcommon
control channels, cell service available,etc
•Radio channelconfiguration
•Current cell + Neighbouringcells
•Synchronizinginformation
•Frequencies + framenumbering
•RegistrationIdentifiers
•LA + Cell Identification (CI) + BaseStation
IdentityCode

51. 51
BCCHSub-Channels
•Frequency CorrectionChannel
•send a frequency correction data burst containing all
zeros to effect a constant frequency shift of RFcarrier
–Mobile station knows which frequency touse
–Repeated broadcast of FrequencyBursts
•SynchronizationChannel
•send TDMA frame number and base station identitycode
to synchronizeMSs
–MS knows which timeslot touse
–Repeated broadcast of SynchronizationBursts

52. 52
CCC
•Access Grant Channel(AGCH)
•BTS toMS
•Used to assign an SDCCH/TCH toMS
•Paging Channel(PCH)
•BTS toMS
•PageMS
•Random Access Channel(RACH)
•MS =>BTS
•SlottedAloha
•Request for dedicatedSDCCH

53. DCCH
•bidirectional point-to-point --mainsignaling
channels
•SDCCH (stand-alone dedicated control channel):
for service request, subscriber authentication,
equipment validation, assignment to a traffic
channel
•SACCH(slowassociatedcontrolchannel):for
out-of-bandsignalingassociatedwithatraffic
channel,eg,signalstrengthmeasurements
•FACCH (fast associated control channel): for
preemptive signaling on a traffic channel, eg,for
handoffmessages
•Uses timeslots which are otherwise used by theTCH
53

54. Localization andCalling
•Localization means same phone number is valid
worldwide
•Periodic locationupdates
•VLR informs the HLR about MS locationchanges
•Changing VLRs with uninterrupted availability of all
servicescalledRoaming
•To locate and address to the MS, GSMneeds
–MSISDN,MSRN
–IMSI,TMSI
•Two ways ofcalling:
–Call Originating from MS(MOC)
–Call termination to MS(MTC)
54

55. OutgoingCall
(MOC)
1.MS sends dialled numberto
BSS
2.BSS sends dialled numberto
MSC
3,4MSC checks VLR if MS is
allowed the requestedservice.If
so,MSC asks BSS to allocate
resources forcall.
5MSC routes the call toGMSC
6GMSC routesthecalltolocal
exchange of calleduser
7,8,
9,10Answer back(ring back)tone
is routed from called user toMS
viaGMSC,MSC,BSS 55

56. IncomingCall
(MTC)
1.Calling aGSM
subscribers
2.Forwarding callto
GSMC
3.Signal Setup toHLR
4.5. RequestMSRN
fromVLR
6.Forwardresponsible
MSC toGMSC
7.Forward Call to
currentMSC
8.9. Get currentstatus
ofMS
10.11. Paging ofMS
12.13. MSanswers
14.15. Securitychecks
16.17. Setup
connection
56

57. HANDOVER
•Single cell do not cover the whole service
area
•Smaller the cell size, faster themovement
of MS, but morehandovers
•However, a handover should not causea
cut-off
•Two reasons to usehandover
–Maintain same quality of radio link atreciever
–Loadbalancing
57

58. HandoverScenario
•Within 1 –IntraCell
•Between 1 and 2–
Inter BTS / Intra
BSC
•Between 1 and 3–
Inter BSC/ Intra
MSC
•Between 1 and 4–
InterMSC
58

59. 59
GSM networks varioussecurity
features
•A wireless radio based network system
quite sensitive to the unauthorized useof
resources
•GSM employ various security features
designed to:
→Designed to protectsubscriber
privacy
→Secured network against misuseof
resources by unregisteredusers

60. 60
GSM networks varioussecurity
features
•Controlled access to the networkby
Mobilestation
•Required to use a PIN before it can
access the network through Uminterface

61. 61
Security inGSM
•SecurityServices:
–Access Control andAuthentication
–Confidentiality : all user dataencrypted
–Anonymity: not disclosed useridentity
•GSM Uses the information stored in AuC andSIM
•SIM protected data with PIN againstunauthorized
use.
•3 algorithms are specified:
-A3 algorithm forauthentication
-A5 algorithm forencryption
-A8 algorithm for keygeneration

62. 62
Authentication
•An AuC (authentication centre) for the
operation and maintenance subsystemof
the GSMnetwork
•Authentication of the Mobilestation
•The AuC first authenticates the subscriber
Mobile station and only then does the
MSC provide the switching service to
another terminalTE

63. 63
Authenticationalgorithm
•Use a random number sent by theAuC
during the connection setup
•An authentication key which is already
saved in theSIM
•Authentication algorithm used differsfor
different mobile serviceprovider

64. AuC sending random number for BTS
andBTS
sending cipher key forencryption
pherkey
Mobile
tion
rBTS
ndom
mber
64

65. Authentication in GSM
65

66. 66
IMSI and TMSI of theMobile
station
•Its publicidentity
•TMSI is the identity granted on movingto
a particularlocation
•When a Mobile station moves to a new
location area, the VLR (visitor location
register) assigns a TMSI which is storedin
the SIM of the Mobilestation

67. 67
TMSI
•The identification of the subscriberduring
communication done not using the IMSI
but theTMSI
•The VLR assigned TMSI generatesthat
ID
•This protects the Mobile stationagainst
eavesdropping from externalsources

68. 68
Encryption
•The BTS and the Mobile stationperform
ciphering before call initiation or before
connecting for receiving acall
•The Mobile station uses acipher
(encryption key) forencryption

69. 69
Thecipher
•A result of performing mathematical
operations on (a) the cipher key saved in
the SIM and (b) the cipher number
received from the BTS when the call setup
isinitiated
•The BTS transmits the cipher number
before a call is set up ortransmitted

70. Encryption
70

71. 71
Advantages of GSM over Analog system
•Capacityincreases
•Reduced RF transmission power and longer batterylife.
•International roamingcapability.
•Better security against fraud (through terminal validationand
userauthentication).
•Encryption capability for information security andprivacy.
•Compatibility with ISDN,leading to wider range ofservices

72. 72
New Data Services:HSCSD
•High Speed Circuit Switched Data(HSCSD)
–Combined several GSM 9.6 Kbps channels to increase
bandwidth
–It allocates several TDMA slots within a TDMAframe
–In theory, an MS could use all 8 slots within a TDMA frameto
achieve an Air Interface User Rate(AIUR).
–Only requires software upgrades in an MS andMSC
•HSCSD exhibits some majorlimitations
–Still uses connection-orientedmechanism
–Not efficient for bursty and asymmetricaltraffic
–Charged based on channelsallocated

73. 73
New Data Services:GPRS
•General Packet Radio Service (GPRS)features:
–It is a 2.5G system, is poised to take off this year inpopularity.
–Building on the GSM network, it will provide the muchneeded
packet data services to most areas of theworld.
–Useful for frequent small volume or infrequentsmall/medium
volume ofdata
–Time slots are not allocated in a fixed or pre-determinedmanner,
but on demand
–Allow broadcast, multicast and unicastservice
–―Always On‖, no connection has to be setup prior to datatransfer
–Resources are reserved only when needed and charged
accordingly

74. 74
GPRS[2]
•It offers point-to-point packet transfer in 2versions
–PTP connection-oriented service(PTP-CONS)
–PTP connectionless service(PTP-CNLS)
•It also offers Multicasting, calledPoint-to-Multipoint
(PTM)service
•User specify QoSprofile
–Service precedence (high, normal,low)
–Reliabilityclass
–Delayclass
–Peak throughput class fordata
–Mean throughput class fordata

75. GPRSArchitecture
BTS
BTS
MS
BSC
Gb
MSC/VLR
HLR/GR
Gn
SGSN
GGSN
Gi
PDN
GGSN
OtherGPRS
PLMN
SGSN
PLMN : GSM Public Land MobileN/w
PDN: Public DataNetwork
Gn
Gn
EIR
75

76. 76
Entities
•The Serving GPRS Support Node(SGSN)
–MobilityManagement
–Authentication
–Requests user information from the GPRS Register(GR)
–Gathers ChargingInformation
•Gateway GPRS Support Node(GGSN)
–Gateway between UMTS Core Network and externalnetworks
–Address allocation forMS
–Gathers ChargingInformation
–Filtering
•Base Station Subsystem (BSS) : BSC,BTS

77. Physical Layer =L1
PLL+RFL =Radio
GMSK= Gaussian minimum shiftkeying
Top Layer =IP/X.25
77

78. LayerFunctionalities
•All data within GPRS backbone (b/w GSNs), is transferred using the
GTP (GPRS TunnelingProtocol).
•GTP can uses two transport protocol TCP andUDP.
•The N/w protocol for the GPRS backbone is IP.
•The SubNetwork Dependent Convergence Protocol (SNDCP) used to
adapt different characteristics of the underlying n/ws b/w an MS and
SGSN.
•On top of SNDCP and GTP, user data packet is tunneled from theMS
to the SGSN and viceversa.
•To achieve a high reliability of packet transfer b/w SGSN and MS,a
special LLC is used, which compute ARQ andFEC.
•A Base Station Subsystem GPRS Protocol (BSSGP) is used to
convey routing and QoS related info b/w BSS andSGSN.
•BSSGP does not perform error correction and works on the top of
frame relay(FR),
•The Radio Link Control (RLC) provides a reliable link, whileMAC
controls access with signaling procedure for radiochannel.
78

79. Future OfGSM
❖2ndGeneration
❑GSM -9.6 Kbps (datarate)
❖2.5 Generation ( Future ofGSM)
❑HSCSD (High SpeedcktSwitcheddata)
➢Data rate : 76.8 Kbps (9.6 x 8kbps)
❑GPRS (General Packet Radioservice)
➢Data rate: 14.4 -171.2Kbps
❑EDGE (Enhanced data rate for GSMEvolution)
➢Data rate: 547.2 Kbps(max)
❖3Generation
❑WCDMA(Wide bandCDMA)
➢Data rate : 0.348 –2.0Mbps
79

80. Thank you