Middleware in Mobile Environments

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Middleware in Mobile Environments

• ICS 280
• Junjun Ouyang

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Architectural Requirements for the Effective
Support of Adaptive Mobile Applications
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Mobile Applications

• CHANGING ENVIROMENT!!!
• availability of resources and services may change
  significantly and frequently during typical
  system operation.
• Be capable of adapting to these changes to ensure
  the best possible level of service

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Research on Mobile Applications

• Early research focused on applications which
  adapted to changes in network characteristics
• Now increasing interest in applications that
  adapt to general environmental and contextual
  triggers such as changes in a system's physical
  location

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Current Approaches to Adaptive Mobile Applications

• Adaptation is performed by the system which
  underpins the application (an attempt to make
  transparent the effects of mobility)
• Applications monitor and adapt to change

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Drawbacks of Current Approaches

• The lack of support for enabling coordination
  between the adaptation policies of multiple
  applications
• Insufficient control over the implications of
  having multiple, and possibly conflicting,
  attributes triggering adaptation

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Problems Scenarios

• Coordinated Application Adaptation for Power
  Management
• multiple applications or system services sharing
  hardware resources
• Conflicting Adaptation
• separate adaptation mechanism for different
  attributes
• coordination or harmonization is desired

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Problems Scenarios

• Using Remote Scenarios
• end-to-end approach requires the monitoring of
  all components involved in the interaction
• Sharing Demand for Network Bandwidth Web
  Browsing and Viewing a Video Stream
• requirement for system-wide adaptation policies,
  for coordinated adaptation

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Directed Flows between Application and Middleware
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Multiple Attributes

• Adapt to a large and heterogeneous set of
  attributes
• The adaptive behavior triggered by one attribute
  can cause side-effects on other attributes

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Architectural Requirements for Mobile Systems

• Supporting a Common Space for an Extensible Set
  of Attributes
• Application Control and Coordination
• Support for System Wide Adaptation Policies
• Distributed Operation

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Typical Middleware Architecture
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Architectural Framework for Future Systems
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Architectural Main Components

• Context Space
• Device Monitors
• Applications and Mechanisms
• Middleware and Mechanisms
• Adaptation Control and Policies

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System Support for Mobile Multimedia Applications
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Trends in Multimedia Applications

• The proliferation of multimedia applications
• The move toward increased system mobility

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Challenges of New Trends -- Potentially
conflicting characteristics

• The proliferation of streaming applications
• resource-hungry
• connection-oriented
• Mobile applications
• radical changes in available resource capacity
• Solution notification
• cause the path changes between peers
• Solution adaptation

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Mobile Multimedia Architecture
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Mobile Multimedia Architecture

• Adaptation methodology based on
• quasi-invariants
• explicit assumptions about the environment
• guards
• used to detect invalidation of quasi-invariants
• intelligent adaptation
• adaptation to a valid set of constraints

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Mobile Multimedia Architecture

• Presentation Specification
• provide user preferences, and hence a framework
  for intelligent adaptation
• Scalable Content
• responsibility for scaling the media stream
• intelligently choose the scaling algorithm best
  suited to media type

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Mobile Multimedia Architecture

• Software Feedback
• informs the application when the data requested
  below or beyond the environment capabilities
• Network and OS Support
• OS responsible for detecting mobility events,
  reconfiguring itself, and supply higher layers
  with mobility indications. (crosslayer
  notifications)

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Architecture of the prototype adaptive
distributed video player
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Implementation-- video player architecture

• Presentation specification
• express users preference on various aspects of
  the video quality
• Scalable content
• supports video clips with multiple spatial
  resolutions

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Implementation-- video player architecture

• Software feedback
• The video player effectively adapts to changes in
  the network and server/client hosts through the
  extensive use the software feedback
• QoS and server/client sync. feedback
• Mobile awareness
• The player uses mobility indications to trigger
  secondlevel feedback operations

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Mobile Multimedia Architecture-- enhancements to
OS

• Implement a device availability model
• Support dynamic network reconfiguration
• Network and OS functionality
• Hot swapping
• Network awareness
• Routing policy
• Device Indication

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Device Availability Support
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Implementation Summary

• Mobility indications force the software feedback
  module into an exploratory mode and cause the
  video client to reestablish the control and data
  channels between it and the server. This allows
  the player to quickly adapt to new environments
  while migrating across heterogeneous networks.

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Related Work

• Application-level gateways
• Network-level gateways
• Link-layer gateways
• Other problems caused by mobility
• High bit error rates (Rutgers I-TCP and
  Berkeleys snoop)
• require more advanced handoff schemes to reduce
  the disruption of real-time multimedia streams

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Summary

• Layered architecture for mobile application
• Each layer performs the adaptation best suited
• methodology of defining quasiinvariants,
  guarding them, and adapting intelligently
• No single layer hides all the effects of mobility
  
• by passing guards on mobilityrelated
  characteristics to lower layers, higher layers
  receive crosslayer notifications and perform the
  scaling and other adaptations best suited
• Player implementation for mobile streaming video

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Agile Application-Aware Adaptation for Mobility
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Outline

• Application-aware adaptation offers the most
  general and effective approach to mobile
  information access
• Odyssey supports concurrent execution of diverse
  mobile applications (with improvement up to a
  factor of 5)
• Agility as a key attribute of adaptive systems
  and describe how to quantify and measure it.

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Problems with mobility-- Adaptation is the key

• Unpredictable variation in network quality
• Wide disparity in the availability of remote
  services
• Limitations on local resources imposed by weight
  and size constraints
• Concern for battery power consumption
• Lowered trust and robustness resulting from
  exposure and motion

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What is Odyssey?

• Odyssey is a set of extensions to the NetBSD
  operating system to support adaptation for a
  broad range of mobile information access
  applications
• These applications execute on mobile clients but
  read or update remote data on servers

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Odyssey Design Rationale

• Motivation Monitors resources and interacts with
  each application to best exploit them
• Fidelity the degree to which data presented at a
  client matches servers reference copy
• Odyssey provide a framework within which diverse
  notions of fidelity can easily be incorporated
• Concurrency Execute multiple independent
  applications concurrently on a mobile client
• centralized monitoring and coordinated resource
  management on a mobile client

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Odyssey Design Rationale

• Agility key property of an adaptive system is
  the speed and accuracy with which it detects and
  responds to changes in resource availability
• the property of a mobile sys-tem that determines
  the most turbulent environment in which it can
  function acceptably
• Minimalism extending an existing system
• the smallest set of interface and code extensions
  we believe necessary for agile adaptation in
  mobile environments

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Odysseys Adaptation Approach

• Application-aware adaptation
• The essence is a collaborative partnership
  between the system and applications
• The system monitors resource levels, notifies
  applications of relevant changes, and enforces
  resource allocation decisions
• Each application independently decides how best
  to adapt when notified

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Odysseys Adaptation Approach

• Division of responsibility directly addresses the
  issues of application diversity and concurrency
• Diversity is accommodated by allowing
  applications to determine the mapping of resource
  levels to fidelity levels
• Concurrency is supported by allowing the system
  to retain control of resource monitoring and
  arbitration.

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Application-Aware Adaptation (Model)
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Application-Aware Adaptation (Realization)

• Two responsibilities for resources management
• Aware of shared access to remote data by
  concurrent applications (properness)
• Have type-specific knowledge (effectiveness)
• Wardens specialized code components incorporate
  type-awareness and encapsulate system-level
  support
• Viceroy type-independent component, for
  centralized resource management

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Application-Aware Adaptation (Realization)

• Collaborative relationship
• data centric
• between viceroy and its wardens
• defines the fidelity levels for each data type
  and factors them into resource management
• action-centric between application and Odyssey
• provide applications with control over the
  selection of fidelity levels supported by the
  wardens

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Implementation goals

• Operate on Odyssey objects
• Express resource expectations
• Be notified when expectations are no longer met
• Respond by changing fidelity

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Odyssey Client Architecture
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Odyssey API
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Applications Video Player
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Applications Web Browser
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Applications Speech Recognizer
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Summary

• The Odyssey architecture supports
  application-aware adaptation
• The essence is a collaborative partnership
  between applications and the system, with a clear
  separation of concerns
• The prototype does a good job of balancing
  performance and fidelity

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A Network Architecture for Heterogeneous Mobile
Computing
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BARWAN Project Outline

• Enables seamless roaming in a single logical
  overlay network composed of many heterogeneous
  (mostly wireless) physical net-works, and
  provides significantly better TCP performance for
  these networks
• Provides complex scalable and highly available
  services to enable powerful capabilities across a
  very wide range of mobile devices, and mechanisms
  for automated discovery and configuration of
  localized services

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Concerns

• How to build this network out of an overlaid
  collection of networks?
• How to seamlessly roam around it?
• How to make it perform well?
• How to leverage computing in the infrastructure
  to enable new abilities and services for even the
  simplest mobile devices?

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Challenges

• Having a ubiquitous localized networking the
  net-work as a whole has broad coverage, but
  connection quality and services vary greatly by
  location
• Need a powerful infrastructure that is highly
  available, cost effective, and sufficiently
  scalable to support millions of users

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Solutions from Architecture

• Seamless mobility both within a network and
  across heterogeneous networks
• A reliable transport layer, based on TCP
• Automatic discovery and configuration of local
  network services
• Remote control of local environments
• Thin clients through dynamic adaptation of content

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Solutions from Architecture

• New abilities for such devices by leveraging
  computation in the infrastructure
• Cluster-based support for scalable, manageable
  and highly available infrastructure services
• A layered programming model for implementing
  services that allows authors to focus on service
  content

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Elements of the BARWAN Architecture
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Layered view of the architecture
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Key Themes

• Dynamic adaptation
• a generic solution to varying network conditions
  and client heterogeneity
• Cross-layer Information
• break the OSI networking model to enable smarter
  adaptation or better performance

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Key Themes

• Agent-base capabilities
• the use of agents in the infrastructure to enable
  new abilities and to hide new problems from
  legacy servers and protocol stacks
• Soft sate
• state that aids in performance or adds
  capabilities, but not required for correctness
• the importance for simplicity, ease of fault
  recovery, and scalability (of agents)

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Overlay Networking

• the unification of several heterogeneous
  networks, of varying coverage and performance,
  into a single logical network that provides
  coverage that is the union of the networks
  coverage with performance corresponding to the
  best network in range
• In addition to traditional cell-based roaming
  (horizontal roaming), they provide transparent
  roaming across the constituent networks (vertical
  roaming), even when this requires changing the IP
  address or network interface

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Wireless overlay network structure
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Elements of the handoff system
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Breakdown of a handoff
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Reliable Data Transport Over Wireless Networks

• In overlay network, the next immediate challenge
  is the poor performance of standard TCP over the
  mobile, wireless and asymmetric networks
• TCP assumptions of congestion losses and
  symmetrical connection may be false
• Solution a combination of TCP enhancements and
  corrective agents (snoop) in the infrastructure
• Hiding the effects of wireless losses and
  asymmetry
• The keys to making agents work well are to
  exploit cross-layer information

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Network topology
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The proxy architecture

• Why Inability of (nearly all) servers to handle
  the incredible variation in software, hardware
  and networking capabilities of mobile clients
• As a smart intermediary between traditional
  servers and heterogeneous mobile clients
• By a powerful agent in the infrastructure to
  adapt content dynamically to support
  heterogeneous networks and mobile devices
• The proxy enables useful access even from very
  simple devices

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Basic proxy architecture
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Dynamic adaptation
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Adaptive Network Services

• IP connectivity is not sufficient
• mobile users need to discover, configure and use
  local services, such as DNS servers, local
  printers, and in-room control of lights and A/V
  equipment.
• This supports seamless interaction with the
  current environment as clients roam in overlaid
  networks
• This enables a far richer environment for mobile
  users, and when combined with the proxy greatly
  simplifies the creation and use of new services

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Mechanism for Adaptive network services

• Service Discovery
• The protocol allows for the maintenance of
  dynamic repositories of service information,
  advertises its availability, and supports queries
  against it
• Remote control
• extend room devices and collaborative
  applications with shared, simplified,
  remote-control interfaces
• Access control based on physical locality (scope)
• embed tickets, random fixed-length bit vectors,
  in the mobility beacons and require the current
  ticket to be included in all communications to
  servers

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Conclusion

• Deployed a really useful working network
• It is possible to roam among several networks and
  the performance of the networks is quite good
• The proxy is highly available and supports
  thousands of users, several quality services, and
  a wide range of mobile devices
• The support for localized network services
  enables automatic configuration of mobile devices