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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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Vision of Mark Weiser
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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Vision of Mark Weiser
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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Vision of Mark Weiser
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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Problems and issues of mobile computing
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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Problems and issues of mobile computing
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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Problems and issues of mobile computing
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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Areas of research in mobile computing
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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Areas of research in mobile computing
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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Areas of research in mobile computing
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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Areas of research in mobile computing
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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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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Problems and Issues of Ubiquitous Computing
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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Problems and Issues of Ubiquitous Computing
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 and Issues of Ubiquitous Computing
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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Problems and Issues of Ubiquitous Computing
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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Problems and Issues of Ubiquitous Computing
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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Problems and Issues of Ubiquitous Computing
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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Problems and Issues of Ubiquitous Computing
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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Problems and Issues of Ubiquitous Computing
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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Problems and Issues of Ubiquitous Computing
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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Problems and Issues of Ubiquitous Computing
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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Problems and Issues of Ubiquitous Computing
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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Problems and Issues of Ubiquitous Computing
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
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