Minimizing DHT Routing Stretch in MANETs
Marcel Cavalcanti de Castro, Andreas Kassler, Gabriel Kliot, Roy Friedman, Raphaël Kummer, Peter Kropf, Pascal A. Felber · 2009
Since the appearance of Napster in early 1999, peer-to-peer (P2P) networks have experienced tremendous growth. The P2P architectures can be categorized into two main classes: unstructured and structured P2P overlays. Unstructured overlays do not impose a rigid relation between the overlay topology and the indices/resources placement, as flooding or random walks are used to locate resources [3]. In contrast, structured P2P networks tightly control the overlay topology by arranging the nodes in a logical structure and by placing content at specified locations that will make subsequent lookups more efficient. Popular representatives of structured P2P networks are realized through the so called Distributed Hash Tables (DHTs), such as Chord [2]. Mobile Ad-hoc Networks (MANETs) usually do not have a dedicated routing infrastructure and rely on multi-hop communication. Nodes in a MANET cooperatively forward other nodes’ data. These networks have a distributed communication architecture, where nodes make individual decisions on routing and medium access. P2P overlay networks in the Internet and MANETs share many key characteristics, such as selforganization and decentralization. However, current P2P overlay architectures can not be directly used as is in MANETs, as it abstract the underlying physical topology during the overlay construction and resource lookup. For example, in Chord, each node has to maintain a set of logical neighbors (successor, predecessor and longrange neighbors) in the virtual identifier space, which requires significant control traffic. Long-range neighbors, also called fingers, are used to quickly route messages to remote locations in the identifier space. Given the limited MANETs bandwidth, the maintenance of logical neighbors can be prohibitively heavy-weight, as the logical neighbors could be located several hops away in the physical wireless topology. While this might be tolerable on the wired Internet with its high bandwidth, it is obviously not feasible for MANETs. Here, the delivery probability of a packet quickly decreases with each physical hop due to factors such as low bandwidth, limited energy, low computation power (of a node), packet collisions, or transmission errors. Therefore, our envisioned DHT implementation combines a minimalist Chord-like overlay structure which replaces the