839181_634335443613367500

Wei Lou @ Department of Computing, Hong Kong Polytechnic Univ.

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COMP 437 Mobile Computing Overview of Mobile Computing

Overview of Mobile Computing


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Outline

What is mobile computing?

Mobile computing applications

Basic concepts of mobile computing

Challenges in mobile computing

Topics in mobile computing


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What is mobile computing?By 2012 the number of mobile subscribers throughout the world will reach 5 Billion, of which close to 1.5 Billion will use wireless communicators (3G) as gateways to the Internet


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What is mobile computing?World wide Internet penetration rate increases rapidly.

25% of the world population access to the Internetby 2012, >1 billion of Internet users will use mobile as their only access means


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What is mobile computing?Today, access to information and computing services is necessary everywhere

not only from our "home base," but also while we are traveling and when we reach a different location.

Mobile computing Techniques that allow mobile users to use portable computing devices to run stand-alone applications and / or to access remote ones via wireless networks.


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What is mobile computing?Mobile computing = mobile + computing, another wave in computing evolution.Different kinds of mobility

Terminal mobility: movement of processors / devices - caused by mobile devices.User mobility: movement of users – caused by traveling people.Logical mobility: movement of processes - caused by mobile codes.

Different modes of computingSmall office: take the service/application with users - computing is offlineHome office: maintain the access to the same service/application at different places – computing is onlineMobile office: move to different places and the service/application follows – computing is moving (follow-me)


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COMP 437 Mobile Computing Overview of Mobile ComputingEvolution of computing

paradigm

2010Unwired

Enterprise

1980

Branch

Age of DistributedComputing

Client/Server

1990

Office

Age of Personal

Computing

Personal Computer

2000

Remote Office

Age of NetworkedComputing

Internet

2003

Mobile Workplace

Age ofMobile

Computing

Mobile Internet

1960

Fixed Location

Age of Centralized Computing

Mainframe


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Mobile computing often uses wireless and mobile networks as access technologies.

Wireless and mobile networks extend networking capacity to cover the areas of lack of wired link and support movement of devices

Wireless communication plays an important role in mobile computing. But, mobile computing does not necessarily mean wireless.

What is mobile computing?


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Wireless mobile Examples

stationary computer

notebook in a hotel room

wireless LANs in historic buildings

Personal Digital Assistant (PDA)

Wireless vs mobile

mobile wireless


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Today’s applications

WAP GatewayMerchant 1

WAP / Agent Server

Merchant n

Internet

ProviderNetwork

WAP Terminal

SQL

SQL

SQL

- WML pages- list of merchants

Products

Products

Internet, Wireless Networks & Mobile ComputingMobile users use wireless communications to access to the Web information and services


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CorporationsM-business / M-office (working remotely - job dispatch, calendar, email, workflow, etc)M-commerce (logistics, inventory control)

ConsumersM-commerce (shopping, banking, payment, etc)Mobile web access / mobile email / SMSMobile P2P (file sharing, gaming, etc.)

Government / Public services / MilitariesM-healthcare (emergency with in-time patient condition info.)TransportationTourism (navigation with maps, location-aware travel hints, etc)Intelligent homeEnvironment monitoringBattle field communications

Today’s applications


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Enabling factorsMotivations and driving forces

Increasing demands on access to information, communication, and cooperation anywhere, anytime, anyway.Technology reality may support such demands

Increasing availability of wireless networks at reduced cost. Widespread use of handheld devices with increasing computing power and lower cost.Integration of communication and computing devices (PDA, i-Phone, smart phone, intelligent sensor).

Advances in techniques of detecting location of a device – location based services.


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Open Mobile Alliance (OMA)

No matter whatdevice I haveservice I wantcarrier or network I am using

I can communicate, access and exchange information

Visions


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Wireless Vision: ubiquitous communication


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Device VisionMobile phones

1973: First cellphone call

2007: ~ 3.3 billion mobile phone subscribers

2009: ~ 4.6 billion

Smart phones are mobile phoneshave operation systemscan connect to the internet: web browsing, email, etchave advanced computing ability: send and receive text & multimedia messages (SMS, MMS), take pictures, etc


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Convergences


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COMP 437 Mobile Computing Overview of Mobile ComputingMobile computing means

more…Mobile computing has a close relationship with distributed computing

Distributed computing: coordination of utilizing computing resources shared by multiple hosts over a network.

Mobile computing: extends distributed computing with new dimensions of mobility and wireless connection.


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more…Mobile computing is also closely related to Internet computing technologies

Mobile computing uses Internet computing technologies

The layered protocol stack and client/server paradigm

Mobile computing allows the application not to connect the network all the time

Mobile Internet, Wireless Internet

HTTP client / server protocols => WAP

XML, HTML => WML, XHTML

J2SE/J2EE, .Net => J2ME/J2EE, .Net Mobile


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more…Pervasive computing

Create a smart environment with ubiquitous, invisible, interconnected devices that provides services to the users without being noticed.

Improving users’ experience and quality of life without requiring them know the underlying technologies.

Mark Weiser, “The Computer for the 21st Century,” Sci. Amer., Sept., 1991.

“The most profound technologies are those that disappear. They weave themselves into the fabric of everyday life until they are indistinguishable from it.”


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Pervasive computing era


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Mobile computing means more…


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Tomorrow…

Pervasive and Mobile ComputingComputing is everywhere, invisible, and moving with you

WLAN Cellular


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Forthcoming applicationsExample: Vehicle Networks

transmission of news, road condition, traffic information, weather, music via DABpersonal communication using mobile phone networkspositioning via GPSlocal ad-hoc network with vehicles close-by to prevent accidents, report traffic jams, guidance system, etcvehicle data (e.g., from busses, high-speed trains) can be transmitted in advance for maintenance busses, trucks, and trains can transmit logistic information for, e.g., fleet management.

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Example: Intelligent lifeSystem knows your current location, and light turns on as you enter a room, and the seat you are sitting on is adjusted to your size.Your active ID-badge indicates your identity (and your preferences). So brightness can be adjusted also based on your preference.Music will continue when you leave a room and enter another.When you enter a range of 5 km of your home, the air-conditioner will be turned on so you get a cool environment upon arriving home.When you attend MTR, you are automatically connected to a group of people sharing the same interest with you in music, sports, games etc.

Forthcoming applications


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What’s the future picture?


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Wireless: Convergence


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COMP 437 Mobile Computing Overview of Mobile ComputingPervasive Internet of

“Things”…

The Economist, April 28, 2007


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Seamless Mobility

1xRTT / GPRSPDA

WiFi / 1x/ 3G PC

GSM / CDMAMobile

DeskPhone

PCLAN

LAN

PBX

DSL

LaptopPC

Headset

HomePhone

Phone

Web Kiosk

Corporate fixed / mobileCommunications

IP

User Mobility

Device Mobility

Network Mobility

PCWLAN

Mobile / PDA(eg. P900)

Work is something you do, not somewhere you goWork is something you do, not somewhere you go


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COMP 437 Mobile Computing Overview of Mobile ComputingChallenges of mobile computing

Where do the challenges come from? Distinct characteristics of mobile and wireless computing:

Wireless communications

Mobility

Mobile devices


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Wireless communicationsBoth wired and wireless communications are about transmission of data by the propagation and processing of signals over a transmission medium

Data – an abstract entity that conveys meaning or informationSignals - electric or electromagnetic representations of data in the physical worldTransmission medium - physical path between transmitter and receiver


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Wireless communications

Transmission mediumGuided Media

Signals are guided along a solid mediume.g., copper twisted pair, copper coaxial cable, optical fiber

Unguided MediaProvides means of transmission but does not guide electromagnetic signalsUsually referred to as wireless transmissione.g., atmosphere, outer space, water


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Wireless communicationsA wireless communication does not use wires (cables) for communications, but by the transmission of electromagnetic waves through ‘the air’.

Michael faraday, James C. Maxwell, Heinrich Hertz

Wireless communication has a long history, started in 1896 - Guglielmo Marconi invented the wireless telegraph

Advances in wireless technology include radio, television, mobile telephone, communication satellites.


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Wireless communicationsElectromagnetic waves are produced and received via antennas

Transmitting antenna - a transmitter delivers radiates alternating current into the surrounding environment in the form of radio or microwave signals

Receiving antenna - converts signals from the environment into alternating current and delivers it to the receiver.


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ChallengesWired channel

Wired channel can be easily engineeredToo many noises? – use shell to protect against electromagnetic noiseLarge signal attenuation? - use repeaters to amplify the signalData rate too low? - upgrade to coaxial cable or optical fiberLow error rate - Good quality: 10-6; Optical fiber: 10-11 ~ 10-12

Wireless channelWireless channel is hardly be engineered

High background noisesSignal strength fluctuates significantlyLow data rateHigh error rate – Radio: 10-2 or worse


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Wired channel – what if more than one transmitter?

Switching Center

or

Network Access Point

Every user accesses the network by means of a dedicated channelNew user is served by a new wired-line circuit

Access capacity is guaranteed.

Dedicated Channel

Challenges


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Wireless channel – what happens?

Base Station

Shared Channel

Wireless users access the network by means of a shared channel

Access capacity is inherently limited.

Challenges


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Wireless channelLow and asymmetric bandwidth

High latency

High error rate

Large variation in available bandwidthBandwidth differences with orders of magnitude from open-space wireless to indoor wireless

Frequent disconnectionsNetwork failure is commonUser’s movement is frequent

Shared radio channelIncreased security risks

Challenges


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Mobility

Different entities of mobility

Physical / Terminal mobility

User mobility

Logical mobility


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MobilityDifferent modes of mobility

Personal mobility : reaching a mobile user using a logical identity, irrespective of what device he/she is using, current location in the network, or even which network he/she is located inSession mobility : maintaining access to the same network service / application at different placesService / application mobility : making a service/application available to mobile user when the user has moved to another location with other but similar resources (e.g., print using the nearest printer) – following me service


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ChallengesDynamic change of physical locations

Mobile users may use their phones at different places

Dynamic change of logical addressesUsers may use their laptops to access different networks

Frequent change of system configuration

Mobile users may use PDAs with cellular networks when outdoor and with WLANs when indoor.


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Location dependencyLocation management problem: How does the network know where the intended recipient of a message is currently located?

Cellular scenario

Where is 97532468?

Send broadcast messages from every base station.

Challenges


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Mobile devices

PagersCellular phonesPortable media playersPersonal digital assistants (PDAs)Tablet PCsLaptop computersMobile Internet devices (MIDs)


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Mobile computing devices are becoming smaller, cheaper, more powerful and better integrated

Small screen display sizeNo keyboard, only some buttonsSmall storage capacityLimited computation capabilityLimited battery powerLarge variations in design & usageFrequent disconnection & a short life span

Challenges


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Need new solutions to old / new problems to overcome the above constraints

Need to Reduce communication and operational costNeed to manage mobilityNeed to conserve energyNeed to design special interfaces for small devicesNeed to enforce wireless security Need to have new computing paradigms

asynchronous interactionshandling of disconnectionsadaptation (may need user’s involvement)mobile code and mobile agent

Cope with challenges


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The challenges can be tackled in various system components including

Mobile devices

Mobile wireless networks and protocols

Location tracking techniquesMobile computing models, application architectures, and software infrastructureProtocols, OS, and programming languagesApplication / user requirements, business models

Cope with challenges


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Wireless communications and networks

Modulation techniques, Multiplexing techniques, Medium access control (MAC), Routing, etc.

Design of different types of wireless networks

Cellular, WLAN, WPAN, WMAN, Satellites

Wireless ad hoc networks (WSN, MANET)


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Wireless communications and networks

Wireless networks can be classified in different ways

Short range vs. Long range

Infrastructured vs. Ad hoc

Heterogeneous


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Wireless communications and networksShort-range wireless pertains to networks that are confined to a limited area.

Local area networks (LAN): cover corporate building, school campuses, manufacturing plants, homes.Personal area networks (PAN): connect portable computers within close proximity to one another.

Operate over unlicensed spectrum reserved for industrial, scientific, medical usage (ISM)

No need to obtain a license, and free of chargeThe most common frequency band is at 2.4 GHzOther bands at 5GHz and 40GHz are also often used.



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Wireless communications and networksLong-range wireless networks span large areas - a metropolitan area, a state or province, an entire country, or across world.

The goal is to provide wider-area or even global coverage

Typically provided by companies that sell the wireless connectivity as a service.

Charging either by the minute or by the amount of data transferred.



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Wireless communication and networksInfrastructure-based wireless networks

mobile computers /devices connect to a wired network via hubse.g., cellular systems (base station infrastructure)e.g., a laptop access internet via WLAN access points


Fixed, wired backbone;Mobiles connectto Access Points.


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Wireless communication and networksAd hoc wireless networks

No infrastructure required, temporarily setup a network to meet immediate needse.g., rescue, home networking, military applicationse.g., wireless sensor networks


No wired backbone;Peer-to-peer;Multi-hop routes


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Wireless communication and networksHeterogeneous networks: integrated network combining different kinds of wireless & wired networks



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Wireless networks issuesThe essential aspects of differrent wireless networks are the same.

They share a common foundation in the design of

physical layer,

median access,

network planning and deployment, and

network operation.



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Mobile computing modelsMobile C/S Models

Simple C/S model, Client/Agent/Server model, Client/Intercept/Server model

Mobile Peer-to-Peer ModelMobile hosts plays the same role and cooperate to Discover peers and resources Route query requests Perform specified tasks

Mobile Agent ModelCode mobility (with computation, data, and state)Autonomous and Asynchronous



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Mobile C/S modelC/S model can still be used in mobile environment - mobile hosts act as the clients requesting service from server located at fixed network.

However, mobile C/S model deviates from the C/S model used for distributed system in several ways. Mobile C/S model cannot assume continuous network connectivity and powerful client ability

RPC (Remote process control) is not suitable due to disconnection; Direct message exchange is not good neither due to weak connectivity and slow network.Need to decouple the communication in synchronous RPC; Use indirection with messages queued at the two ends.



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Mobile C/S modelNo clear division of functionality between mobile client and server at the fixed networkResource limitation on mobile client justifies moving client activities to server side (“thin client”); However, client can not be too “thin”, since disconnection and low bandwidth force us to place some processing ability on client for disconnected operations (“smart client”)

Need synchronization between client and server



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Mobile C/S issuesOptimization

Data compressing / filtering

Mobile date managementData dissemination and broadcast

Caching and invalidation

Disconnected operations

Location based services

Context-aware adaptation



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Mobile P2P modelNo central server, actually no difference between client and server:

All nodes have the same role, serving as both server and clientRelying on collaboration

Completely decentralized & asynchronous operationsNodes can communicate with each other directly



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Mobile P2P applicationsData sharing and disseminationInstant messagingCollaborationEntertainment (e.g., gaming)…



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Mobile P2P featuresGood programming model for ad hoc network

Good architecture for cooperative applications

Server side can also move: more flexible

Good system scalability

Both sides need resource rich devices

Complexity in protocol design



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Mobile P2P issuesRapid mutual peer discovery and connection establishment

Message routing between peers

Data sharing among peersSearching / discovery (routing of queries)

Caching and invalidation

Security



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Mobile agent (MA) modelA MA is a “process on the move” – dispatched by one host, encapsulating a thread of execution along with a package of code, data, and execution state

Executes at a host for a while, halts execution, dispatches itself to another host, and resumes execution there - all under its own control

mobile agent X

logic

mobile agent X

logic

Host A Host B

Migratingmobile agent

X

logic



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Mobile agent featuresMobility

Actively travels across the network, carrying partial / intermediate results calculated at the previous hostNot just alternative to message passing; can perform additional tasks along its way of traveling

AutonomousDecides by itself what to do and how, when and where it ought to move

AsynchronyMobile agents and users can execute at the same time without blocking each other



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Mobile agent advantages

Reducing remote communicationPerform tasks locally: save network bandwidth

Intermediate result data is processed locally rather than transferred back and forth over the network

Go to the data if the data can’t come to you



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ClientAgent Service

ServerHost

MA model of service MA model of service providingproviding

Client

Host

Service

ServerNetwork

Network


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Mobile agent advantages

Overcome message passing latency

Local, “instant” interaction with the other party

Latest up-to-date information

Be adaptiveCan encapsulate policies and protocols



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Mobile agent advantagesSupport disconnected/intermittent connectivity, slow network.

Support disconnected/weak connectivity operation



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Mobile agent applications

Especially good for those mobile computing applications

Require long connection time and/or user has bad connection/highly mobility

User can disconnect and do something else while mobile agent performing tasks over the network

E.g., information search, retrieval, filtering, E-commerce, network management, etc.



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Mobile agent applications

Site B

Site A Site C

Site D

Dispatch

Computing

ComputingComputing

Computing

Site EReceive



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Site B

Site A Site C

Site D

Dispatch

Computing

Computing Computing

Computing

Site E

collaborating

Topics in mobile computingMobile agent applications


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Mobile agent issuesNeed powerful mobile devices if need to have mobile agent platform installed on devices

Fault tolerance

Security issue is the main obstacle



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Mobility managementTypes of mobility management

Handoff management

Location management

Mobility management in cellular networks

Mobility management in Mobile IP

Location services in MANET



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Protocols / algorithms for resource-constrained mobile environments

MAC protocols

Routing protocols

Clustering

Synchronization

Data dissemination

Data aggregation


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Location based servicesMobile positioning techniques

Cellular phone positioning Network-based vs Handset based solutions

GPSWLAN positioningOther technologies (in-door, road beacon, identity)

Location-based servicesGIS

LBS architecture



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Mobile computing middleware

Service discovery in mobile computing

Security in mobile computing

Reliability in mobile computing



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Related journal & conferences

IEEE Transactions on Communications IEEE Transactions on Parallel and Distributed SystemsIEEE/ACM Transactions on Networking IEEE Transactions on Vehicular TechnologyIEEE Transactions on Computers Transactions on Mobile ComputingMobile Networks & ApplicationsIEEE Communications MagazineMobile Computing and Communications ReviewProceedings of the MOBICOMProceedings of the MOBIHOCProceedings of the INFOCOMProceedings of the GLOBECOMProceedings of the Vehicular Technology ConferenceProceedings of ICDCS…

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