Mobile and Ubiquitous Computing

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Mobile and UbiquitousComputing Spring 2007 1

Mobile and Ubiquitous Computing

A background and overview

Vision of Mark Weiser

Challenges and Issues of Mobile Computing

Challenges and Issues of Ubiquitous Computing


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Reference Papers

[1] The Computer for the 21st CenturyMark Weiser,Palo Alto Research Center

1991, Scientific American

Reprinted in Pervasive Computing

January March 2002

[2] Fundamental Challenges in Mobile Computing

M. Satyanarayanan,Carnegie Mellon University

Published in 1996 in ACM (PODC96)

[3] Pervasive Computing: Vision and ChallengesM. Satyanarayanan,Carnegie Mellon University

Published in IEEE Personal CommunicationsAugust 2001


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Preview

The convergence of technologies

Issues pointed to by Mark Weiser

Problems and issues of Mobile Computing Five major research areas

Problems of Ubiquitous Computing

Integration of different technologies Major areas of research


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An Interesting Scenario Jane is at Gate 23 at the Pittsburgh airport, waiting for her

connecting flight

She would like to use her wireless connection to e-mail anumber of large documents Many passengers at Gates 22 and 23 are surfing the Web Aura observes that Jane wont be able to finish sending her

documents before her flight departs After consulting the airports flight schedule service, Aura

discovers that wireless bandwidth is excellent at Gate 15 A dialog box pops up on Janes screen suggesting that she

go to Gate 15, which is only three minutes away It also asks her to prioritize her e-mail, so that the most

critical messages are transmitted first Jane accepts Auras advice and walks to Gate 15 Aura informs her that it is close to being done with her

messages, and that she can start walking back The last message is transmitted during her walk, and she is

back at Gate 23 in time for her boarding call [3]


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Specialized elements of hardware and software,connected by wires, radio waves and infrared, willbe so ubiquitous that no one will notice theirpresence

Ubiquitous

Invisible computers embedded in everyday objects thatwould replace PCs

Technology should disappear to make computers ubiquitous

Issues:Scale and the knowledge of where the user is located toadapt to the surroundings


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Embodied virtuality

Modified virtual realityProcess of drawing computers out of theirelectronic shells

Devices that implement the technologyInteraction between devices is more important thanmaking them

Parts that build a ubiquitous system Low cost and low power computers Software Network that ties the computer together


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The Computer Hardware is satisfactory

The Operating System needs a changeMicrokernel approach

Network requirements:

Transparent and wireless link between modules

Protocols that are efficient in mobile networks

A large number of channels

A future where computers disappear


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Problems and issues of mobile computing

Constraints of mobile computing and their impact ondistributed systems

All constraints are intrinsic to mobility Mobile elements are resource poor Mobility is inherently hazardous Mobile connectivity is highly variable Mobile elements rely on a finite energy source

Solution lies in the mobile client being

ADAPTIVE


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Adaptive implementation has two extremes

Total autonomy: Adaptation is the responsibility ofthe individual application

Application transparent adaptation: Responsibility of

adaptation lies entirely on the system

Actual implementation lies between the twoextremesApplication aware adaptation

Use an extended client-server modelto implement

mobile application The client may have to take the role of a server


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Experimental results on Coda file systemExperiment conducted to study the effect ofmobility and application transparent adaptation

1. Disconnected operation is feasible, effective and

usableUse techniques of hoarding, update logging andreintegration on reconnection

2. Optimistic replica control strategy is applicable

Use techniques of log-based directoryresolution, application-specific file resolution,containment and manual repair


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Experimental results on Coda file system.3. Support weak connectivity to avoid the limitations of

disconnected operationsUse techniques of adaptive transport protocols,rapid cache validation mechanism, trickle

reintegration mechanism and model-basedcache miss handling

4. Use isolation-only transaction to cope with detectionand handling of read-write conflicts during

disconnected operationsUse database transactions

5. Server replication can be used to complementdisconnected operation


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Areas of research in mobile computing

Five areas of research are identified1. Caching Metrics

Problems of common metric - Miss ratio

Should be consistent and easy to monitor

Open problems: What is an appropriate set of caching metrics for

mobile computing?

Under what circumstances does one use each

metric? How does one efficiently monitor these metrics?

What are the implications of these alternativemetrics for caching algorithms?


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2. Use cache validation instead of maintainingcache coherence to reduce remotecommunication Use callbacks

Maintain cache coherence at multiple levels of

granularity

Use semantic validation to maintain cachecoherence at multiple levels of granularity

Open questions are related to predicate Q that

is a function of the block value P How useful are semantic validation and callbacks?

What forms can P and Q take for data types?


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3. Algorithms for resource revocation Application aware adaptation complicates the problemof resource management

Open problems are: How does one formulate the resource revocation

problem? How does one characterize the differential impact of

revocation on different applications? What strategies does one use if multiple resources

must be simultaneously revoked? How does one distinguish between resources whose

revocation is easy to recover from and those which areexpensive or impossible to recover from?

How does one handle deadlocks during revocation


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4. Analysis of adaptation

Primary figure of merit for mobile clients: Agility

Ideal mobile client is highly agile and very stable

Open questions:

What are the right metrics to measure agility?

Are there systematic techniques to improve the agility ofa system?

How does one decide when a mobile system is agileenough?

What are the right metrics to measure system stability?

Can one develop design guidelines to ensure stability?

Can one analytically derive the agility and stabilityproperties of an adaptive system without building it?


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5. Global estimation from local observations

Adaptive mobile clients should have the capability to inferglobal changes by detecting local changes

Issues are:

Are there systematic ways to perform global estimation fromlocal observations?

Can one bind the error in global estimates?

What is the relationship between global estimation and agilityof adaptation?

Can one provide system support to improve global estimation?

Can one quantify the benefits of out-of-band channels?


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Problems and Issues of Ubiquitous Computing

Pervasive Computing

Technology that disappears

Relationship with distributed systems and mobilecomputing

Problems solved in distributed systems

Remote communication

Fault tolerance

High availability

Remote information access

Security Key constraints of mobility forced the development of

specialized techniques

Four areas of research in ubiquitous computing


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2005-2006 M. Satyanarayanan intro-18

Remote communicationprotocol layering, RPC, end-to-end args . . .

Fault toleranceACID, two-phase commit, nested transactions . . .

High Availabilityreplication, rollback recovery, . . .

Remote information accessdist. file systems, dist. databases, caching, . . .

Distributed securityencryption, mutual authentication, . . .

Distributed

Systems

Mobile networkingMobile IP, ad hoc networks, wireless TCP fixes, . . .

Mobile information accessdisconnected operation, weak consistency, . . .

Adaptive applicationsproxies, transcoding, agility, . . .

Energy-aware systemsgoal-directed adaptation, disk spin-down, . . .

Location sensitivityGPS, WaveLan triangulation, context-awareness, . . .

MobileComputing

Smart spaces

Invisibility

Localized scalability

Uneven conditioning

PervasiveComputing

How Did We Get Here?


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Areas of research:

Effective use of smart spaces context-aware space

Invisibility minimal user distraction

Localized scalability

Masking uneven conditioningsmartness of environments

varyFirst requirement for any application is proactivity

All technologies for implementing the scenario is available

Whole is much greater than simply the sum of its parts

Requires seamless integration of component technologiesProblems lie in the architecture, component synthesis andsystem level engineering


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User

Immersed in a PC environment

Adaptable and reconfigurable

Client

May take the role of a server

A multilayered architecture

Environment

Smart spaceServer


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The structure of an Aura Client


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Problems that need to be solved

User intent needs to be established

A number of research questions need to beanswered

Deal with the conflicting requirement of higher

functionality and limited resources

Use available resources in the smart space

Cyber foraging and surrogate of mobile computing

Cyber foraging living off the land exploit wired hardwareinfrastructure

Hardware starts playing the role of surrogateof the mobilecomputer


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Areas to explore

Cyber foraging

Adaptation strategies

High level energy management

Client thickness

Context awareness

Balancing proactivity and transparency

Privacy and trust Impact on layering


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Cyber foraging gives rise to a number ofresearch problems

Discover the presence of surrogates

Level of trust with a surrogate

Load balancing Time to stage

Effect of scalability

System support needed for seamless andminimally intrusive surrogate


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Adaptation strategies Client may guide the application to reduce fidelity

Use reservation based Quality of Service

Client may suggest the user a corrective action

Unanswered questions: Factors that affect the decision to choose between the

adaptation strategies

Is reservation based QoS the best strategy?

Multiple and competing requests for reservations Practicality of adaptation using corrective actions

Methods of lowering fidelity


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Mobile and Ubiquitous

Computing Spring 2007 26


High level energy management High level system should get involved for energy

management

Energy aware memory management

Unanswered questions Methods of managing energy

Impact on invisibility

Can knowledge of user intent be exploited in energymanagement?

Use of smart spaces and surrogates to reduce energydemand

Remote execution to extend battery life


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Client thickness

The clients need to be as thin as possible but should bethick enough to fulfill the requirements

Research questions are:

Quantify client thickness and environmental conditioning

Can the system alert a user when it migrates to a lesshospitable environment?

Is transparent migration from a thinner to a thicker clientpossible?

Can computers be reconfigured to serve as optimal mobile

clients under diverse environmental conditions? Can semi-portable infrastructure be carried with a user to

augment less hospitable environments?


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Context awareness Required for a minimally intrusive computing

system

Issues:

How is context represented internally? How frequently does context information need

to be consulted?

Minimal services that the environment needs

to provide What are the relative merits of various

location-sensing technologies?


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Balancing proactivity and transparency Both are important requirements

Proactive systems may not always work well

Transparency is especially important in distributedsystems with scarce resources

Unanswered questions

How are individual user preferences and tolerancesspecified and taken into account?

How is it possible to determine the balance?

Can the existing balancing mechanisms be used toprovide a systematic design guideline to applicationdesigners?


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Privacy and trust

System contains detailed information related to a user

User trust is achieved by keeping the informationstrictly confidential and private

Research issues Balance between seamless system behavior and the

need to alert users to potential loss of privacy

What are the authentication techniques best suited topervasive computing?

How is access control enforced using the identity ofusers?


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Impact on layering

Layering techniques help solve large problems

Helps hiding some details but exposes others that arerequired to solve a problem

Issues are: Preserving the benefits of layering while

accommodating the needs of ubiquitous computing

Are existing layers best extended for pervasivecomputing by broadening their primary interfaces or

creating secondary interfaces?

What is the complexity involved in design andimplementation of layers for ubiquitous computing?


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Areas exploredrecent publications

Research areas (2005-2006)

Internet suspend/resume (ISR) VM technology and Distributed File systems

Same hardware architecture at least to ISAlevel

Remote execution

Cyber foraging

Resource monitoring and predictingresource demands


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Conclusion

Challenging research problems exist inthe field of Mobile and UbiquitousComputing

Integration of technologies is the mainissue

HCI, Software agents, AI are other areasthat are integrated in the field

A lot has been achieved

More to be explored


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Thank you

Documents

Mobile and Ubiquitous Computing