Dynamic Reconfiguration Support for Pervasive Computing

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Dynamic Reconfiguration Support for Pervasive
Computing

• Dongman Lee
• Collaborative Distributed Systems Networks Lab.
• Information and Communications Univ.

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Contents

• Overview
• Key Requirements
• Case Study
• Technical Challenges

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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.
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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

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Key Characteristics of Ubiquitous Computing

• Human-centered
• Distraction-free
• Minimal administration
• Context-aware
• Invisibility
• Ideal complete disappearance of pervasive
  computing technology from a users 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

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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
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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

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Key Considerations

• Adaptability
• 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

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Aura - Overview

• Aura Objectives
• 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 layers 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

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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

Aura System Architecture
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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
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Gaia - Overview

• Gaia Objectives
• 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

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Gaia - Architecture

• Gaia System Software
• 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

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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
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Active Surroundings - Overview

• Active Surroundings
• 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

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Active Surroundings - Architecture
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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

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Active Surroundings Interaction Model
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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 applications 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

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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

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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
  developers role)
• If it allowed, follow ontology description
  (described by service provider)

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Technical Challenges in System Support

• Technical Kindberg
• Service discovery
• Adaptation
• Integration with physical world
• Programming framework
• Robustness
• Security

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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 doesnt 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 humans role to
  resolve tension between interoperability and
  ambiguity

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Discovery and interaction (contd)

• Interaction
• 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

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Adaptation

• Challenges
• 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

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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

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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

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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

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Security

• Challenges
• Trust
• 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 users 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

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Q A

• What would you like to see in future?

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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 22-31.
• Ralph D. Hill, The Abstraction-Link-View
  Paradigm Using Constraints to Connect User
  Interfaces to Applications, Proceedings of
  CHI92, pages 335-342.
• 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.