A Reliable Multicast Mechanism for Sensor Network Applications (2005)

A Reliable Multicast Mechanism for Sensor Network Applications * Lewis Girod Martin Lukac Andrew Parker Thanos Stathopoulos Jeffrey Tseng Hanbiao Wang Deborah Estrin Richard Guy Eddie Kohler Center for Embedded Networked Sensing University of California, Los Angeles Los Angeles, CA, 90095 USA Los Angeles, CA 90095 USA {girod,mlukac,adparker,thanos,hbwang,desthn,rguykohler}@cs. ucla.edu, jeffreyt@icsl.ucla.edu ABSTRACT As the field of embedded networked sensing matures, useful abstractions are emerging to satisfy the needs of increasingly complex applications. This paper demonstrates StateSync, an abstraction for reliable dissemination of application state through a multi-hop wireless network. Using StateSync, the complexity of multihop wireless network applications and services can be reduced to processing a gradually evolving set of table entries, subject to minimal consistency checks. The StateSync abstraction defines a data model based on key-value pairs, a reliability model w i t h a probabilistic la­ tency bound, and an event-driven publish/subscribe A P I . We evaluate StateSync using three different applications. We present performance measurements using simulation and a wireless testbed. model for received values published by a single node, but does not attempt to guarantee consistency between received values published by different nodes. Using StateSync, the complexity of the multihop wireless network is reduced to processing a gradually evolving set of table entries, subject to certain minimal consistency checks. Application Requirements T H E STATESYNC ABSTRACTION Embedded networked sensing applications inherit a long list of application requirements that are more or less unique among distributed systems. The main distinguishing char­ acteristic is a high degree of dependence on the environment, in the face of dynamic conditions and a limited capability to discover environmental properties w i t h certainty. Proper­ ties of the environment often affect both system performance and the application's objectives, and thus must be estimated to achieve the system's goals. These issues are at the heart of the design of successful system components for embedded networked sensing applications. We designed StateSync to extend the ideas of previous abstractions [16] and protocols [12] to support of a specific class of applications. These applications have the following properties: • Reliable delivery greatly simplifies the design of the application. • A relatively large amount of data is shared, and fresh­ ness of the data is important, including assurance that the publisher of data is still active. • The data being shared exhibits low churn , meaning that the expected lifespan of a data element is long compared w i t h the system latency requirements. One example of this type of application is an acoustic localisation system. Such a system needs to disseminate range estimates throughout the network in order to fuse them into a coordinate system. These range estimates vary slowly over time in response to minor changes, occasion­ ally changing abruptly when nodes are moved. Reliabil­ ity is important for this application, because inconsistent or stale data can present problems for the multilateration al­ gorithm. The range data in this application tends to have As the field of embedded networked sensing matures, use­ ful abstractions are emerging to satisfy the needs of i n ­ creasingly complex applications. This paper demonstrates StateSync, an abstraction for reliable dissemination of ap­ plication state through a multi-hop wireless network. The StateSync layer presents a publish/subscribe inter­ face to a set of application-defined tables. The contents of these tables are reliably and efficiently broadcasted a spec­ ified number of hops away, using a protocol that is robust to changes to the network topology and changes in the re­ ceiver set. StateSync conforms to a minimal consistency *This work was made possible w i t h support from the NSF Cooperative Agreement CCR.0120778, and the U C M I C R O program (grant 01-031) w i t h matching funds from Intel. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise to republish, to post on servers or to redistribute to lists> requires prior specific permission and/or a fee. Copyright 200X ACM X-XXXXX-XX-X/XX/XX ...$5.00.