Framework of an Application-Aware Adaptation Scheme for Disconnected Operations

1
Framework of an Application-Aware Adaptation
Scheme for Disconnected Operations

• Umar Kalim, Hassan Jameel, Ali Sajjad, Sang Man
  Han, Sungyoung Lee, and Young-Koo Lee
• Department of Computer Engineering,
• Kyung Hee University
• dated 2005/11/23

2
Background

• Hand-held devices using a wireless network
• Environment conditions such as network bandwidth
  varies due to user mobility
• Service may be disrupted as a result of
• Network bandwidth dropping below a threshold
• Out of range
• Example scenario
• Hospitals environment/rescue team
• Junior doctors need to diagnose patients

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Wireless Access Point
Below threshold
Within range
Out of range
4
Research Objective

• Devise a mechanism that allows the system to
  automatically reconfigure itself in order to
  maintain service availability (even with
  poornetwork bandwidth)

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Proposed Solution

• Mobile computing middleware (Remote Evaluation
  paradigm)
• Reflection
• Code mobility
• Adaptation scheme is application aware
• The framework allows the developer to determine
  the application policies

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Proposed Solution

• Dynamically reconfigure the application
• Redeploy components - when online a offline

Operates according to the remote evaluation
paradigm
Before
Certain objects (with their states) are relocated
to the client platform and continues its
operation
After
Example Implementation
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Types of Disruptions

• Voluntary disconnections
• User initiated event
• Knowledge in advance enable the system to
  prepare for preparation
• Involuntary disconnections
• Unplanned network failure
• No knowledge in advance - need to detect
  disconnection, require to be pessimistically
  prepared for it, and pro-actively prepare a
  response
• Remedy is the same

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How is it Achieved

• Floating objects
• Deal with the process of adaptation to
  disconnected operations
• Based on a distributed object framework
• Allow the redeployment of components
• Code mobility and dynamic binding
• Java class loader and Java Reflection API
• Ability to replace objects substitute for
  remote implementations
• Transfer of State
• Java Serialization/De-serialization
• DisconnectionManagement Interface
• disconnect and reconnect

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Classification of Components for Disconnection

• Log
• After disconnection, the invocations that are
  made on this reference are logged locally
• Substitute
• Upon disconnection , a temporary but local
  reference should be used to replace the remote
  reference
• It may have a different (or limited)
  functionality
• Replica
• The reference should be replicated and
  transferred to the client for local execution to
  maintain service availability
• Reconnection latest, revoke, prime, merge

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Classification of Components for Reconnection

• Latest
• The state of the reference with latest time-stamp
  is maintained while the other is discarded
• Revoke
• The entire changes made on the replicated or
  substituted reference are dropped in favor of the
  state of the original reference
• Prime
• Contrary to revoke references
• The state of the original reference is discarded
  in favor of the Prime reference
• Merge
• Neither the replicated/substituted reference nor
  the original reference is clearly identified to
  be maintained
• There is a need for conflict detection and
  resolution techniques
• All disconnection-aware references may implement
  the Merge interface
• Whenever a reconnection occurs, the system would
  invoke the merge method for reconciliation by
  using callback mechanism

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State Transitions
Module Layout
Class diagram framework
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Real-Time Effectiveness
How long does a disconnection take? How long does
the process of reconciliation take?
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Related Work

• Commonly used techniques
• Caching 1
• Hoarding 2
• Queuing remote interactions 3
• Replication and replica reconciliation 1
• Multi-modal components 4
• Architectural reconfiguration 5
• Exact algorithm - Complexity - O(kn-m)
• Stochastic algorithm - Complexity - O(n2)
• Adaptive greedy algorithm - Complexity - O(n3)

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Conclusion Future Work

• Programming model to maintain service
  availability even in the face of disconnections
• Code mobility
• Reflection
• Application in Delay Tolerant Networks (DTNs)
• Operational issues of predicting a disconnection
  in the face of fading bandwidth

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Questions CommentsThanks
Please feel free to contact us for further
details at the following addresses

• Young-Koo Lee
• yklee_at_khu.ac.kr

Umar Kalim umar.kalim_at_gmail.com
Department of Computer Engineering, Kyung Hee
University, Suwon, South Korea.
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Selected References

• J. J. Kistler and M. Satyanarayanan. Disconnected
  Operation in the Coda File System. ACM
  Transactions on Computer Systems, vol. 10, no. 1,
  February 1992
• G. H. Kuenning and G. J. Popek. Automated
  Hoarding for Mobile Computers. Proc. of the 16th
  ACM Symp. on Operating Systems Principles, St.
  Malo, France, October, 1997
• A. D. Joseph, et. al., Rover a toolkit for
  mobile information access, 15th ACM Symposium on
  Operating Systems Principles, December 1995,
  Colorado
• Y. Weinsberg, and I. Ben-Shaul. A Programming
  Model and System Support for Disconnected-Aware
  Applications on Resource-Constrained Devices.
  Intl Conf. on Software Engr., Orlando, Florida,
  May 2002
• M. Mikic-Rakic and N. Medvidovic. Support for
  Disconnected Operation via Architectural
  Self-Reconfiguration
• M. Shepperd et al. Comparing Software Prediction
  Techniques using Simulation, IEEE Transactions,
  2001.
• Please refer to our paper for further details