No abstract

The Internet has fallen prey to its most successful service, the World-Wide Web. The networks do not keep up with the demands incurred by the huge amount of Web surfers. Thus, it takes longer and longer to obtain the information one wants to access via the World-Wide Web. Many solutions to the problem of network congestion have been developed in distributed systems research in general and distributed file and database systems in particular. The introduction of caching and replication strategies has proven to help in many situations and therefore these techniques are also applied to the WWW. Although most problems and associated solutions are known, some circumstances are different with the Web, forcing the adaptation of known strategies. This paper gives an overview about these differences and about currently deployed, developed, and evaluated solutions.

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In mobile wireless networks communication is often improved by sending messages along a stable backbone of more reliable communication paths. Building such a backbone requires efficient clustering algorithms which aggregate network nodes into logical groups, each group being managed by a clusterhead and any two neighboring clusters being interconnected by at least one gateway node or gateway path. In this concept -hop clustering refers to cluster structures where cluster members are at most hops away from their clusterhead. While the dynamicity of mobile wireless ne tw o rk is o fte n c o nside red as a c h a llen g e , in th is w o rk w e explicitly exploit node mobility in order to support cluster formation and maintenance of -hop clusters. The described KHOPCA algorithm consists of a set of easy to implement rules which form and maintain -hop sized clusters in a purely localized way. In a static network cluster formation is limited to a constant number of messages exchanges among neighboring nodes. In dynamic networks the localized nature of the described rules promise a fast cluster convergence and low communication complexity in case of mobility triggered cluster reconfiguration.

Abstract-Clustering techniques create hierarchal network structures, called clusters, on an otherwise flat network. In a dynamic environment-in terms of node mobility as well as in terms of steadily changing device parameters-the clusterhead election process has to be re-invoked according to a suitable update policy. Cluster re-organization causes additional message exchanges and computational complexity and it execution has to be optimized. Our investigations focus on the problem of minimizing clusterhead re-elections by considering stability criteria. These criteria are based on topological characteristics as well as on device parameters. This paper presents a weighted clustering algorithm optimized to avoid needless clusterhead reelections for stable clusters in mobile ad-hoc networks. The proposed localized algorithm deals with mobility, but does not require geographical, speed or distances information.