Middleware 2003

ACM/IFIP/USENIX International Middleware Conference

Rio Othon Palace Hotel

Rio de Janeiro, Brazil

16-20 June 2003

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Website Mirror at the University of São Paulo

Full Paper Abstracts

Opportunistic Channels: Mobility-aware Event Delivery

Yuan Chen, Karsten Schwan and Dong Zhou (Georgia Tech. and DoCoMo Labs)

The delivery of data in pervasive systems is subject to constraints imposed by end host mobility.
A resulting problem is how to create appropriate, application-level data provisioning topologies, termed
data brokers, to best match underlying network connectivity, end user locations, and the locales of
their network access. Another problem is how to balance workloads in such overlay networks, in
response to mobility and to changes in available processing and communication resources.
This paper improves the performance of data provisioning by dynamically changing broker topologies
and by changing end users' assignments to brokers. Specifically, using publish/subscribe as a
communication paradigm, a new abstraction, termed an  opportunistic event channel, enables dynamic
broker creation, deletion, and movement. Experimental and simulation results demonstrate the 
ability  of opportunistic channels to optimize event delivery and  processing when end users move
across different network  access points. The technique is to `opportunistically' follow network level
handoffs across network access points with application-level handoffs of a user's broker functionality
to a new, `closer' broker. The potential load imbalances across brokers caused by such handoffs are
also addressed. Opportunistic channels are realized with the JECho event infrastructure. Performance
advantages attained from their use can be substantial, with the cost of sending a message from a
publisher to a mobile subscriber improved by up to 50%. Furthermore,load balancing improves event 
delivery even for moderate numbers of event subscribers.

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