What is Mobile Computing?Wireless Communication SystemsMobile Communication Systems ArchitectureKey Technologies of Mobile ComputingApplications

Key Technologies of Mobile ComputingPositioningMobility managementRoutingMobile agent

Positioning Needs of PedestrainsGPSindoor

Positioning TechnologiesConcepts of positioningSatellite-based solutionsNetwork-based solutionsIMU-based solutions

Concepts of Positioningsurvey network infrastructureBS ()

Comparisons of Positioning TechnologiesSatellite-based solutionshigher hardware cost (terminal-based positioning)function well in outdoor environments [] example: GPS, A-GPS, D-GPSNetwork-based solutionsneed communication infrastructure [e.g. base station]more suitable in indoor environments [infrastructure]example: WiFi, PHS, GSM

IMU (Inertial Measurement Unit)-based solutionsextra hardware cost [G-sensor () M-sensor ()]without any infrastructure supportinherently accumulated errors []usually operate as auxiliary component

Satellite-Based SolutionsTriangulation (Trilateration)triangulationGPSBSTOA (Time of Arrival)trilateration: a method for determining the intersections of three sphere surfaces given the centers and radii of the three spheres.measure distances or angles of at least three reference pointsusually need specific hardware supportswidely used in many positioning systems, such as GPS

GPSGPSdistance is measured by time of arrival (ToA) []need very precise time synchronization1s time shift will result in 300m distance errorGPS systemsUSA: GPSRussia: GLONASSEurope: GalileoChina: Beidou

Data Transferred from SatellitesConstellation [] of 24 satellitesL1 frequency for civilian useL2 frequency for military and government use1500 bits/frame, 50bps (pretty low) [frameGPS]Time of week, TOW

Data Transferred from SatellitesBroadcast Ephemeris [;()] (accurate position)Almanac [;]At least 30 sec. for first fix [30 secLBS30 sec]

AGPS (Assisted GPS)GPSs weaknessesTTFF (Time To First Fix) of GPS > 30 seconds (average case: 2~3 min)signal cannot be correctly received in buildings or sheltered areasPossible solutionsA-GPSBSFCC: a preferred solution for E911operators: no need to change telecommunication infrastructure

AGPS Concept

Positioning Errors of GPSStandard Positioning Service (SPS)C/A-Code (Coarse/Acquisition Code)SA (Selective Availability)2000US ArmySA150m2000SA25mLBShorizontal accuracy: 100mvertical accuracy: 156mcommercial use

Deviation is more than 5 metersweather errormultipath errorGDOP (Geometric Dilution of Precision)receiver errorEphemeris errorSA (Selective Availability)cycle slips

DGPS (Differential GPS)Goal: increase the accuracy of positions derived from GPS receiversUse base receivers with known locations nearby the GPS receivers to achieve high positioning accuracy (< 5m) [(corrections)]

The cost of build-in GPS chip is more than 10% of the material cost of mobile phonesThe number of mobile phones equipped with GPS

OBSERVATION

Americans time spent indoors: 89%transport: 6%outdoors: 5%

Network-Based PostioningPropertiesneed communication infrastructuremore suitable in indoor environmentsexample: WiFi, PHS, GSMSite surveydeployment of base stationsradio mapCategoriescell-IDtriangulation / trilaterationfingerprinting

Cell-ID LocalizationError = 200m~1kmUserBSsite surveyBSCell-ID localization ()

Triangulation LocalizationProblems:propagation attenuation,multipathBS multipath

Fingerprinting LocalizationIndoor is better, error = 3m1. 2000Microsoft Lab 2. site survey BS (Radio Pattern)3. DB ( )4. Skyhook Wireless Technology Used in Revolutionary iPhone and iPod touch (802.11)5. indoor (3m)

IMU-Based PositioningPropertieswithout any infrastructure supportinherently accumulated errorsusually operate as auxiliary componentExtra hardware costinertia referencerelative acceleration (G-Sensor [], Pedometer [;] Function)relative angle (M-Sensor [], Compass Function)

Summary of Positioning TechnologiesA reliable and ubiquitous positioning technology is the key factor of LBSThere is no dominating positioning technologyHybrid positioning may be the answer

SMS for LocationSimple format for mobile phones short message service []Google Maps and Google Latitude support announce location via SMS (proprietary format).

Source: GPS

OPEN GeoSMS

ExamplesOMIA,1;2504.8015,N;12133.9766,E;1;101,02-81018898,GeoSMS/2;2502.01,N;12133.851,E;P;101/02-81018898/

Source: GPS

Application: Car Accident Insurance Process

Key Technologies of Mobile ComputingPositioningMobility managementRoutingMobile agent

Mobile Management Cellular System

GSM System Architecture

GSM Location Area Hierarchy

Handoff

Inter-LA Registration

Inter-MSC Registration

Inter-VLR Registration

Call Origination Procedure

Call Termination Procedure

Mobile Management Mobile IPv4Mobility issues in IP Networksonce a mobile terminal moves to a new subnet, a correspondent node needs to use the mobiles new IP addressit is difficult to force every possible correspondent node to keep track when a mobile terminal may change its IP address and what the mobiles new address will bechanging IP address will cause on-going TCP sessions to break

Mobility management shouldensure on-going TCP connection does not breakrestore quickly if TCP connection breaks

Home NetworkHome addressa globally unique and routable IP addresspreconfigured or dynamically assignedHome networkthe network whose network address prefix matches that of the mobile terminals home addressHome agent (HA)maintain up-to-date location information for the mobileintercept packets addressed to the mobiles home addresstunnel packets to the mobiles current location

Note: Network PrefixClass A Network (/8 Prefixes)Class B Networks (/16 Prefixes)Class C Networks (/24 Prefixes)

*IP addresses are divided into three different classeseach of the following figure defines different-sized network and host partsthere are also class D addresses specify a multicast group, and class E addresses that are currently unused in all cases, the address is 32 bits long

*IP addresses: (a) class A; (b) class B; (c) class C

*the class of an IP address is identified in the most significant few bitsif the first bit is 0, it is a class A addressif the first bit is 1 and the second is 0, it is a class Bif the first two bits are 1 and the third is 0, it is a class C addressof the approximately 4 billion (= 232)possible IP addressesone-half are class Aone-quarter are class Bone-eighth are class C

*Class A addresses7 bits for the network part and 24 bits for the host part126 (= 27-2) class A networks (0 and 127 are reserved)each network can accommodate up to 224-2 (about 16 million) hosts (again, two are reserved values)Class B addresses14 bits for the network part and 16 bits for the host part65,534 (= 216-2) hosts

*Class C addresses21 bits for the network part and 8 bits for the host part2,097,152 (= 22l) class C networks254 hosts (host identifier 255 is reserved for broadcast, and 0 is not a valid host number)

*IP addresses are written as four decimal integers separated by dotseach integer represents the decimal value contained in 1 byte (= 0~255) of the address, starting at the most significanteg., 171.69.210.245 Internet domain names (DNS)also hierarchicaldomain names tend to be ASCII strings separated by dots, e.g., cs.nccu.edu.tw

Foreign NetworkCare-of Address (CoA)assigned to the mobile by the foreign networka mobile uses its CoA to receive IP packets in the foreign network

Foreign agent (FA)provides CoAs and other necessary configuration information (e.g., address of default IP router) to visiting mobilesde-tunnels packets from the tunnel sent from a visiting mobiles HA and then delivers the packets to the visiting mobileacts as the IP default router for packets sent by visiting mobile terminalshelps visiting mobiles to determine whether they have moved into a different network

Two Types of COAs in MIPv4Foreign Agent CoAan IP address of a FAeach FA is responsible for providing FA CoAs to visiting mobileswhen FA CoA is used, the mobiles HA tunnels the packets to the mobiles current FA that addressed to the mobiles home addressthe FA will then de-tunnel the packets and deliver them to the mobile

Co-located CoAa CoA acquired by a mobile terminal through any method external to Mobile IPexample, a mobile may use the Dynamic Host Configuration Protocol (DHCP) to obtain a temporary address dynamicallythe mobile terminals HA tunnels the packets addressed to the mobiles home address directly to the mobile itself; these packets do not have to go through any FA

Key Technologies of Mobile ComputingPositioningMobility managementRoutingMobile agent

Ad Hoc Routing ProtocolsAd hoc routing protocols must deal withhigh power consumptionlow bandwidthhigh error ratesAd hoc routing protocols categorytable-driven source-initiated (demand-driven)

DSDVCGSRWRPAODVDSRLMRABRSSRTORA

Table-Driven Routing ProtocolsTable-driven routing protocols maintain consistent, up-to-date routing informationrequire each node to maintain one or more tables to store routing informationProtocolsDestination-Sequenced Distance-Vector Routing (DSDV)Clusterhead Gateway Switch Routing (CGSR)Wireless Routing Protocol (WRP)

Source-Initiated On-Demand Routing ProtocolsSource-initiated on-demand routing protocols creates routes only when desired by the source nodeSome routing schemeAd Hoc On-Demand Distance Vector Routing (AODV)Dynamic Source Routing (DSR)Temporally Ordered Routing Algorithm (TORA)Associativity-Based Routing (ABR)Signal Stability Routing (SSR)

Ad Hoc On-Demand Distance Vector Routing (AODV)A source node initiates a path discovery process whendesires to send a message does not already have a valid routePath discoverybroadcasts a route request (RREQ) packet to its neighbors neighbors then forward the request to their neighbors until either the destination or an intermediate node with a "fresh enough" route to the destination is located

Propagation of the PREQ

RREQ & RREPintermediate nodes record the address of the neighbor from which the first copy of the broadcast packet is received if additional copies of the same RREQ are later received, these packets are discardedonce the RREQ reaches the destination, the destination node responds by unicasting a route reply (RREP) packet back if a route entry is not used within the specified lifetime, the route will be deleted

Path of the RREP to the Source

Key Technologies of Mobile ComputingPositioningMobility managementRoutingMobile agent

What is a Mobile Agent?Mobile Agent (Intelligent Message) an electronic message carries a computer program either procedural or declarative it can be executed by the receiving servers on behalf of the originating client the program in the message can instruct a receiving server to forward the message to another server continuously in a pipeline fashion

Mobile Agent Model

The agent model is based on the concepts of places and agents places places provide the environment for executing mobile agents a place is entirely located on a single node of the underlying network an agent system consists of a number of these places

agents mobile agents are active entities, which may move from place to place to meet other agents and to access the places' services an agent can be identified by a globally unique agent identifier, which is generated at the agent's creation time and is not changed throughout its life communication between agents may be local or global

Example of a Mobile Agentl : 2 : (airline A)3 : 4 : AVIS5 : 6 : 7 : 8 : (PCsmart phone)9 : 10 :

Mobile Agent Itinery

Classification of Agents in a Mobile Agent SystemMobile agents Service agents system services application-level services

Types of Agents CommunicationAgent / service agent interaction [client/server]Mobile agent / mobile agent interaction [peer-to-peer]Anonymous agent group interaction User / agent interaction

Agent / Service Agent Interaction Service agents are the representatives of services in the agent world, the style of interaction is typically client/server Services are requested by issuing requests, results are reported by responses An RPC-like communication mechanism should be provided

Client Server Paradigm

Mobile Agent / Mobile Agent InteractionThe rule of the communication partners in this type are peer-to-peer rather than client/server Each mobile agent has its own agenda and hence initiates and controls its interactions according to its needs and goals

Mobile Agent Paradigm

Why Mobile Agents for Mobile Computing?Resolve the problems with wireless communications noisy expensive low bandwidth unreliable (intermittent connection) limited battery lifeScalable clients

Resource optimization if an agent's goals require extensive communication with a particular resource on the network, moving closer to the resource can reduce or eliminate network traffic, allowing the agent to perform its duties more quicklyDistributed parallel processing agents can move to lightly loaded machines when necessary and delegate subtasks to other mobile agents, allowing true parallel processing

Reliability mobility and autonomy allow an agent to move from its point of origin into a network and continue to operate, even if the originating device is temporarily or permanently disconnected from the networkby doing so, the agent can provide services and satisfy predefined goals without user intervention

Mobile Agent Systems

Sheet1

Mobile Agent SystemAuthorLanguageSecure CommunicationServer ResourceAgent Protection

TelescriptGeneral MagicCreated their ownAgent transfer is authenticatedCapability-basedNot supported

OO, type-safeusing RSA and encryptedresource access. Quotas

languageusing RC4can be imposed.

Authorization based on

agent's identity

TacomaCornell UniversityTcl, but is createdNot supportedNot supportedNot supported

University of Tromso,to be written in other

Norwayscripting languages

D'AgentsDartmouth CollegeTcl interpreter, mo-Uses PGP for authenticationUses safe-Tcl as itsNot supported

dified to executeand encryptionsecure execution envireon

scripts and capturement. No support for

state of execution atowner-based authorization

thread level

AgletsIBMJava. IBM developedNot supportedStatically specified accessNot supported

a separate classrights, based on only two

library to createsecurity categories:

mobile agentstrusted and untrusted

VoyagerObjectSpaceJava. Unique featureNot supportedProgrammer must extendNot supported

is a utility whichSecurity Manager. Only

takes any Java classtwo security categories:

and creates a remo-native and foreign.

tely-accessible ver-

sion of it.

ConcordiaMitsubishi ElectricJava. Has ItineraryAgent transfer is encrypted andSecurityManager screenAgents protected from

object, which keepsauthenticated using SSLacceses using a staticallyother agents via the

track of an agent'sconfigured ACL based onresource access

migration pathagent owner identitymechanism

AjantaUniversity ofJavaTransfer is encrypted usingCapability-based resourceMechanisms to detect

MinnesotaDES and authenticated usingaccess. Authorizationtampering of agent's

ElGamal protocolbased on agent's ownerstate and code

Sheet2

Sheet3

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***********Step 1: BCCH(LAC, Location code) SDCCH new VLR MS Temporary Mobile Subscriber Identity (TMSIVLR VLR MSC VLR : MSC, TMSI, old LAI, target LAI .Step 2:IMSI VLR VLR TMSI VLR IMSI VLR authentication TMSI IMSI Step 3: VLR HLR VLR IMSI MS PLMN, i.e., HLR HLR VLR Step 4: VLR TMSI Step 5:3HLR VLR VLR

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