Document Type

Technical Report

Publication Date

2-1-2004

Technical Report Number

TR2004-488

Abstract

Reactive or proactive mobile applications require continuous monitoring of their physical and computational environment to make appropriate decisions in time. These applications need to monitor data streams produced by sensors and react to changes. When mobile sensors and applications are connected by low-bandwidth wireless networks, sensor data rates may overwhelm the capacity of network links or of the applications. In traditional networks and distributed systems, flow-control and congestion-control policies either drop data or force the sender to pause. When the data sender is sensing the physical environment, however, a pause is equivalent to dropping data. Arbitrary data drops are not necessarily acceptable to the reactive mobile applications receiving sensor data. Data distribution systems must support application-specific policies that selectively drop data objects when network or application buffers overflow. In this paper we present a data-dissemination service, PACK, which allows applications to specify customized data-reduction policies. These policies define how to discard or summarize data flows wherever buffers overflow on the dissemination path, notably at the mobile hosts where applications often reside. The PACK service provides an overlay infrastructure to support mobile data sources and sinks, using application-specific data-reduction policies where necessary along the data path. We uniformly apply the data-stream ``packing'' abstraction to buffer overflow caused by network congestion, slow receivers, and the temporary disconnections caused by end-host mobility. We demonstrate the effectiveness of our approach with an application example and experimental measurements.

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