Curt Cramer

Bootstrapping locality-aware P2P networks

Bootstrapping is a vital core functionality required by every peer-to-peer (P2P) overlay network. Nodes intending to participate in such an overlay network initially have to find at least one node that is already part of this network. While structured P2P networks (e.g. distributed hash tables, DHTs) define rules about how to proceed after this point, unstructured P2P networks continue using bootstrapping techniques until they are sufficiently connected. In this paper, we compare solutions applicable to the bootstrapping problem. Measurements of an existing system, the Gnutella web caches, highlight the inefficiency of this particular approach. Improved bootstrapping mechanisms could also incorporate locality-awareness into the process. We propose an advanced mechanism by which the overlay topology is - to some extent - matched with the underlying topology. Thereby, the performance of the overall system can be vastly improved.

Proximity neighbor selection for a DHT in wireless multi-hop networks

A mobile ad hoc network (MANET) is a multi-hop wireless network having no infrastructure. Thus, the mobile nodes have to perform basic control tasks, such as routing, and higher-level tasks, such as service discovery, in a cooperative and distributed way. Originally conceived as a peer-to-peer application for the Internet, distributed hash tables (DHTs) are data structures offering both, scalable routing and a convenient abstraction for the design of applications in large, dynamic networks. Hence, DHTs and MANETs seem to be a good match, and both have to cope with dynamic, self-organizing networks. DHTs form a virtual control structure oblivious to the underlying network. Several techniques to improve the performance of DHTs in wired networks have been established in the literature. A particularly efficient one is proximity neighbor selection (PNS). PNS has to continuously adapt the virtual network to the physical network, incurring control traffic. The applicability of PNS and DHTs for MANETs commonly is regarded as hard because of this control traffic, the complexity of the adaptation algorithms, and the dynamics of a MANET. Using simulations supported by analytical methods, we show that by making a minor addition to PNS, it is also applicable for MANETs. We additionally show that the specifics of a MANET make PNS an easy exercise there. Thus, DHTs deliver good performance in MANETs.

Bootstrapping chord in ad hoc networks not going anywhere for a while

With the growing prevalence of wireless devices, infrastructure-less ad hoc networking is coming closer to reality. Research in this field has mainly been concerned with routing. However, to justify the relevance of ad hoc networks, there have to be applications. Distributed applications require basic services such as naming. In an ad hoc network, these services have to be provided in a decentralized way. We believe that structured peer-to-peer overlays are a good basis for their design. Prior work has been focused on the long-run performance of virtual peer-to-peer overlays over ad hoc networks. In this paper, we consider a vital functionality of any peer-to-peer network: bootstrapping. We formally show that the self-configuration process of a spontaneously deployed chord network has a time complexity linear in the network size. In addition to that, its centralized bootstrapping procedure causes an unfavorable traffic load imbalance

On the fundamental communication abstraction supplied by P2P overlay networks

The disruptive advent of peer-to-peer (P2P) file sharing in 2000 attracted significant interest. P2P networks have matured from their initial form, unstructured overlays, to structured overlays like distributed hash tables (DHTs), which are considered state-of-the-art. There are huge efforts to improve their performance. Various P2P applications like distributed storage and application-layer multicast were proposed. However, little effort was spent to understand the communication abstraction P2P overlays supply. Only when it is understood, the reach of P2P ideas will significantly broaden. Furthermore, this clarification reveals novel approaches and highlights future directions. In this paper, we reconsider well-known P2P overlays, linking them to insights from distributed systems research. We conclude that the main communication abstraction is that of a virtual address space or application-specific naming. On this basis, P2P systems build a functional layer implementing, for example lookup, indirection and distributed processing. Our insights led us to identify interesting and unexplored points in the design space. Copyright

Reactive clustering in MANETs

Many clustering protocols for mobile ad hoc networks (MANETs) have been proposed in the literature. With only one exception so far (1), all these protocols are proactive, thus wasting bandwidth when their function is not currently needed. To reduce the signalling traffic load, reactive clustering may be employed.We have developed a clustering protocol named “On‐Demand Group Mobility‐Based Clustering” (ODGMBC) (2), (3) which is reactive. Its goal is to build clusters as a basis for address autoconfiguration and hierarchical routing. In contrast to the protocol described in ref. (1), the design process especially addresses the notions of group mobility and of multi‐hop clusters in a MANET. As a result, ODGMBC maps varying physical node groups onto logical clusters. In this paper, ODGMBC is described. It was implemented for the ad hoc network simulator GloMoSim (4) and evaluated using several performance indicators. Simulation results are promising and show that ODGMBC leads to stable clusters. This stabilit...