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

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 –Hospital’s environment/rescue team –Junior doctors need to diagnose patients

Out of range Below threshold Within range Wireless Access Point

Research Objective Devise a mechanism that allows the system to automatically reconfigure itself in order to maintain service availability (even with poor network bandwidth)

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

Proposed Solution Dynamically reconfigure the application –Redeploy components - when online  offline Example Implementation Operates according to the remote evaluation paradigm Before After Certain objects (with their states) are relocated to the client platform and continues its operation

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

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

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

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

State Transitions Module Layout Class diagram – framework

Real-Time Effectiveness How long does a disconnection take? How long does the process of reconciliation take?

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(k n-m ) –Stochastic algorithm - Complexity - O(n 2 ) –Adaptive greedy algorithm - Complexity - O(n 3 )

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

Questions & Comments Thanks Young-Koo Lee Umar Kalim Department of Computer Engineering, Kyung Hee University, Suwon, South Korea. Please feel free to contact us for further details at the following addresses

Selected References 1.J. J. Kistler and M. Satyanarayanan. Disconnected Operation in the Coda File System. ACM Transactions on Computer Systems, vol. 10, no. 1, February 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, A. D. Joseph, et. al., Rover: a toolkit for mobile information access, 15th ACM Symposium on Operating Systems Principles, December 1995, Colorado 4.Y. Weinsberg, and I. Ben-Shaul. A Programming Model and System Support for Disconnected-Aware Applications on Resource-Constrained Devices. Int’l Conf. on Software Engr., Orlando, Florida, May M. Mikic-Rakic and N. Medvidovic. Support for Disconnected Operation via Architectural Self-Reconfiguration 6.M. Shepperd et al. Comparing Software Prediction Techniques using Simulation, IEEE Transactions, Please refer to our paper for further details