tough - On optimal cooperative route caching in large...

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On optimal cooperative route caching in large, memory-limited wireless ad hoc networks Theodoros Salonidis and Leandros Tassiulas , Department of Electrical and Computer Engineering University of Maryland, College Park, MD, USA Department of Computer and Communication Engineering University of Thessaly, Volos, Greece [email protected], [email protected] Abstract — Caching is a popular mechanism for enhancing performance in various layers and applications of computer networking. We introduce both a model and algorithms for caching routing information in large, memory-limited wireless ad hoc networks. Each host can cache only a small fraction of the network and must rely on flooding to acquire information that has not been locally cached. To constrain flooding, the network uses a cooperative caching model where every node provides its route cache contents to others when they flood. Given the host memory capacity limitations, we are faced with the problem of allocating destinations to caches in an efficient manner. We propose the class of Best State/Best Cost (BSBC) cooperative caching algorithms that aim to minimize the overall network search effort. I. INTRODUCTION We consider a static wireless ad hoc network with a large number of memory-limited nodes. A representative application is a sheer number of sensors deployed in an area to perform various sensing and communication tasks. Due to memory limitation, nodes cannot maintain routing information for the entire network and use an on-demand ad hoc routing protocol [1][2][3]. According to such a protocol, a node caches routing information only for a subset of the intended destinations. If a non-cached route is needed, the node initiates a search pro- cedure by flooding the network with route discovery packets. Upon reception of a discovery packet, the destination replies to the source with the routing information (e.g. path) collected by the discovery packet. Route discovery can potentially cover a large part of the network, yielding a high flooding cost. In ad hoc networks, the flooding cost translates not only to delay and communication control overhead but also to consumption of node power resources. Minimization of transmissions is crucial for power conservation and extension of the overall network lifetime. The network uses expanding ring search and cooperative caching [2][3] to limit the flooding cost. In expanding ring search, each discovery packet is marked with a ”Time To Live” (TTL) field, decreasing as the packet propagates through the network. If the destination is not found, a larger horizon route discovery restarts by issuing new discovery packets with increased TTL. The process continues until the destination is found. However, a discovery can still be costly if the destination is located many hops away. Cooperative caching [2][3] advocates the use of any intermediate node that has cached the destination. Since routing information can be provided by non-destination nodes,
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This note was uploaded on 03/19/2012 for the course CS 1313 taught by Professor Aman during the Spring '12 term at Punjab Engineering College.

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tough - On optimal cooperative route caching in large...

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