1. Dynamic Reconfiguration Support for Pervasive Computing
Dongman Lee
Collaborative Distributed Systems & Networks Lab.
Information and Communications Univ.

2. Contents
Overview
Key Requirements
Case Study
Technical Challenges

3. Paradigm Shift
Technology is moving from personal computers to handheld, intelligent, and everyday devices with embedded technology and connectivity
From Pervasive Computing: Vision and Challenges by Satyanarayanan, M.

4. Ubiquitous Computing Vision
The most profound technologies are those that disappear. They weave themselves into the fabric of everyday life until they are indistinguishable from it – Mark Weiser
Computation is freely available everywhere – IBM
People, places, and things are first class citizens of the connected world, where e-services meet the physical world, where humans are mobile, devices and services are federated and context-aware – HP
Brings computing away from the desktop and into the world, where people live and work – Microsoft
Provides each user with an invisible halo of computing and information services that persists regardless of location – CMU
By extending the reach of traditional computing systems to encompass the devices and physical space surrounding the machines, entities, both physical and virtual, may be allowed to seamlessly interact – UIUC

5. Key Characteristics of Ubiquitous Computing
Human-centered
Distraction-free
Minimal administration
Context-aware
Invisibility
Ideal – complete disappearance of pervasive computing technology from a user’s consciousness
Practical – reasonable approximation to this ideal – minimal user distraction
Not only hardware but also software
Hardware aspect (physically invisible)
Tangible interfaces, smart appliances, etc.
Software aspect (logically invisible)
Not intrude to users, self-configure, self-adaptive system

6. Key Features of Ubicomp Middleware
To Support “Pervasiveness”, the system should provide the followings:
Sense environment changes
Provide mechanisms to gather the sensed information
Sensed should be converted to context information
Decision should be made by itself to provide efficient services to users without intrusion to the user
Service discovery mechanism to discover currently available service based on current context
New services or devices should be dynamically plugged into system without interventions of users
The changed information should be distributed to other entities in the environment
Environment Sensing
Context Management
Service Discovery
Dynamic Reconfiguration Support

7. Why Dynamic Reconfiguration?
Motivation
Heterogeneity
Ubiquitous computing environment contain a collection of heterogeneous devices (resources)
Different environments have different number of resources
Dynamics
Not only devices but also users dynamically enter and leave an environment
Multi-users
Group of users share an environment
Dynamic Reconfiguration Support
Polymorphic and Transparent Application Transformation with minimal administration
Applications are dynamically and automatically adapted to current context
Efficient use of resources – system aspect
User context (preference) – user aspect

8. Key Considerations Adaptability Flexibility Transparency
Dynamic and heterogeneous nature of a ubiquitous computing environment
Applications are dynamically and automatically adapted to current context with minimal intrusions to users
Flexibility
Different environments have different devices and services
We may not assume that exactly same service (or devices) are available in environments
Transparency
Allow applications to spontaneously reconfigure with new services or established services regardless of context changes

9. Aura - Overview Aura Objectives Challenges Two Broad Concepts in Aura
Intended for pervasive computing environments involving wireless communication, wearable or handheld computers, and smart spaces.
Aims to provide User distraction-free computing environment
Moving workspace
Challenges
Human attention is an especially scarce resource in pervasive environment
Minimize distraction or intrusion of system
Variable bandwidth connectivity, short battery life, and client resource constraints in mobile communication
Two Broad Concepts in Aura
Proactivity
A system layer’s ability to anticipate requests from a higher layer
Self-tuning
Layers adapt by observing the demands made on them and adjusting their performance and resource usage characteristics

10. Intelligent Networking
Aura - Architecture
Aura Components
Odyssey
Resource monitoring and application-aware adaptation
Coda
Support for nomadic, disconnectable, and bandwidth-adaptive file access
Spectra
Adaptive remote execution mechanism that uses context to decide how to best execute the remote call
Prism
Responsible for capturing and managing user intent
Layered above application and provides high-level support for proactivity and self-tuning
Intelligent Networking
Linux Kernel
Coda
Nomadic file access
Odyssey
Resource Monitoring, Adaptation
Spectra
Remote Execution
Other Aura runtime support
Application
Prism
Task Support, user intent, high-level proactivity
Aura System Architecture

11. Aura - Adaptation
Coarse-grained Adaptation (Application Re-composition or reconfiguration)
Ongoing work (does not provide yet)
Focus on Inter-environment Task Migration
Describe Current Task
Leverage Aura File Space (Extended Coda) to store task description
Restore current task using task description
Bird eye view of Aura Adaptation
Description of Video Playing Service

12. Gaia - Overview Gaia Objectives Challenges
People-Centric Pervasive Environment
Mobile users in pervasive computing environment
Many resources, devices per user
Resource management and infrastructure for pervasive computing
Context sensitive adaptation of applications, services, and resources
Challenges
Software infrastructure with which to develop applications for ubiquitous computing habitats or living spaces
Unified infrastructure for Active Space
Active Space
A physical space coordinated by a responsive context-based software infrastructure that enhances mobile users’ ability to interact with and configure their physical and digital environments seamlessly

13. Gaia - Architecture Gaia System Software Application Framework
Gaia Kernel
Component Management Core
Dynamically loads, unloads, transfers, creates, and destroys all Gaia Components
Event Manager
Supports creation of named event channels and distribution of load
Context Service
Provides a taxonomy and uniform representation of context types
Context File System
Make personal data automatically available to applications, conditioned on user presence
Component Repository
Provides persistent storage of components
Presence Service
Detects the presence of digital and physical entities
Space Repository
Centralized repository containing information about active entities
Gaia Architecture
Application Framework
Model – Presentation – Controller – Coordinator Application Framework
Model
Implements the application logic
Presentation
Exports the application data
Controller
Maps input sensor events into method requests for the model
Coordinator
Manages the first four components

14. An Example of Group-aware Application (MP3 Player) Policy
Gaia - Adaptation
Manual Adaptation
Provide GUI to select appropriate presentations and controllers
Automatic Adaptation
Use policies to drive application adaptation automatically
Generate ACD from AGD with predefined policies
GUI for Manual Adaptation
An Example of Group-aware Application (MP3 Player) Policy
ACD generator

15. Active Surroundings - Overview
Explore ways in which surroundings are enabled to socially interact with themselves as well as human beings by embodiment of cognition, learning, emotion, behavior, etc.
Active, not just reactive
Surroundings are tangible, sociable, and cooperative
Explore the context of groups as well as individuals
Develop a framework by which surroundings can assist and help human beings, exploiting location- or context-aware understanding dynamically and adaptively
Dynamic reconfiguration support
Develop an application model suitable to a ubiquitous environment where there exist heterogeneous and dynamic resources, devices, services, security policies, etc.
Provide application developers with an infrastructure with which they can develop applications transparently without concerning the context changes or target environments
Allow flexible application adaptation to such a heterogeneous and dynamic environment

16. Active Surroundings - Architecture

17. Active Surroundings – Key Points
Application Model
Extended Presentation/semantic split application model
An application is composed of a semantic object and one or more presentation objects
Application can polymorphically change its presentations, exploiting currently available resources or devices in an environment
Transparent Adaptability Support
Virtually connected communication bus with a pub/sub model
Supports two distinct adaptation semantics: anchored vs. localized
Application developers can be relieved from being burdened on dealing with context changes
Flexibility Support
Application adaptation based on sub-typing concept
Application can be flexibly reconfigured to current contexts

18. Active Surroundings – Interaction Model

19. Active Surroundings – Application Model
Application Model – Extended Presentation/Semantic Split Model
Presentation object
A software abstraction created in an environment with devices
Partially replicate state information
Semantic object
Implements logic of the application and manage the application’s state
PS link
Contains constraints and define how to access information in presentation and semantic objects
Presentation Architecture
Automatic mappings of presentation objects when context changes
Advantages
Association of a single semantic object with multiple presentation objects
Multi-user support
Effective use of resources (devices)
Application access independent of local presentations

20. Active Surroundings – Adaptation Support
Transparent Adaptability Support
Assumption
Publish/subscribe communication model
Provides service objects with the interfaces for interacting with other service objects
For dynamic binding, service objects are dynamically bound at runtime using event type matching
Service link
Acts as a proxy for local communication broker
Represents how service objects (and associated link objects) are associated with each other
Rebinds each of link objects when an application is introduced to a new context
 Only link object is required to rebind itself to a new communication broker due to context changes while application object remains intact

21. Active Surroundings – Flexible Binding
Flexibility Support
Leverages notion of sub-typing concept
The required service and operation is transparently substituted by 3 cases; substitution by its sub-type, substitution by its super-type, or coercion by its super-type functionality
Subtyping Policy
Substitution with subtype
Searching level
Subtype searching process will be continued till one of its subtype find (default)
Replace with supertype
In case of additional functionality
Depend on the application policy (application developer’s role)
If it allowed, follow ontology description (described by service provider)

22. Technical Challenges in System Support
Technical [Kindberg]
Service discovery
Adaptation
Integration with physical world
Programming framework
Robustness
Security

23. Discovery and interaction
Service discovery
address allocation and name resolution
Challenges
avoiding overspecification
Components must obey the same vocabulary and syntax of service specifications
Lost opportunities for association
A camera that can send an image for printing should be able to send the image to a digital frame. But, if the camera doesn’t have a specification for the digital frame, the opportunity passes
More abstract and much less detailed service specifications can lead to ambiguity
System designers must decide the human’s role to resolve tension between interoperability and ambiguity

24. Discovery and interaction (cont’d)
After associating to a service, a component employs a programming interface to use it
Challenges
How can the software on the device use the service without a priori knowledge of its methods ?
Data-oriented interaction is a promising model
It requires ubiquitous data standardization for it to work across environment boundaries

25. Adaptation Challenges Content adaptation
Adaptation must often take place without human intervention, to achieve calm computing
Embedded devices tend to be small, and limits to miniaturization mean constrained resources
Available resources tend to vary dynamically
Content adaptation
The content adaptation techniques in mobile computing solve only a part of the overall problem
Content adaptation among n heterogeneous device types
We must address such issues as discovery and robustness
We must find a way to apply the adaptation using mechanisms invisible to the user
The human interface adaptation
It is to move the human interface to a physically different device chosen on the fly
Applying transformation to the UI can be a powerful approach to achieving spontaneous interaction

26. Integration with the physical world
Challenges
We need low-level application programming interfaces that let software deal with physical sensors and actuators
We need a high-level software framework that lets applications sense and interact with their environment, including physical sensors and actuators

27. Programming frameworks
A framework for programming ubiquitous computing environments might address the ubiquitous computing challenges in applications, the operating system or middleware, and the development language
Challenges
to leverage existing applications
because of large investment in the applications, their data, and knowledge of how to use them
to leverage OSs without modification
OSs are fragile, most users are reluctant or insufficiently sophisticated to apply OS patches, and OS functionality is generally regarded as beyond application writers’ control

28. Robustness and routine failures
Challenges
A radical increase of failure frequency due to wireless networking
Solutions
Expiration-based schemes and soft state
Each available device or service send a periodic advertisement announcing its presence or availability to the directory service
When failure is common case, identify what critical static or dynamic state you must persistently store and consider reconstructable soft state for the rest
Separating failure-free and failure-prone operations
Indicate which operations are more likely to fail which enables developers to be able to provide more effective error handling
Group communication for “free” indirection
to provide a level of indirection that helps rediscover lost resources

29. Security Challenges Trust Security for resource-poor devices
Because of spontaneous interoperation
Security for resource-poor devices
Extremely resource-poor devices do not have sufficient computing resources for asymmetric encryption
Protocols must minimize communication overheads to preserve battery life
Access control
Knowing an identified user’s whereabouts raises privacy issues
Location
Customizing services to a location can result in a loss of privacy for identified individuals
New patterns of resource-sharing
Physical integration works against the firewall model
Spontaneous interaction makes extranet technologies unsuitable, because developers intend them for long-term relationships with outside users

30. Q &A
What would you like to see in future?

31. References
Manuel Roman, Christopher K. Hess, Renato Cerqueira, Anand Ranganathan, Roy H. Campbell, and Klara Nahrstedt, Gaia: A Middleware Infrastructure to Enable Active Spaces, IEEE Pervasive Computing, pages 74-83, Oct-Dec 2002.
David Garlan, Dan Siewiorek, Asim Smailagic, and Peter Steenkiste, Project Aura: Towards Distraction-Free Pervasive Computing, IEEE Pervasive Computing, special issue on Integrated Pervasive Computing Environments, Volume 1, Number 2, April-June 2002, pages
Ralph D. Hill, The Abstraction-Link-View Paradigm: Using Constraints to Connect User Interfaces to Applications, Proceedings of CHI’92, pages
Glenn E. Krasner and Stephen T. Pope, A Description of the Model-View-Controller User Interface Paradigm in the Smalltalk-80 System, Journal of Object Oriented Programming, vol. 1(3), pages 26-49, 1988.
Barbara H. Liskov and Jeannette M. Wing, A Behavioral Notion of Subtyping, ACM Transactions on Programming Languages and Systems 1994.