Kendy Kutzner

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.

Measuring Large Overlay Networks — The Overnet Example

Peer-to-peer overlay networks have grown significantly in size and sophistication over the last years. Meanwhile, distributed hash tables (DHT) provide efficient means to create global scale overlay networks on top of which various applications can be built. Although filesharing still is the most prominent example, other applications are well conceivable. In order to rationally design such applications, it is important to know (and understand) the properties of the overlay networks as seen from the respective application.

Improving delivery ratios for application layer multicast in mobile ad-hoc networks

Delivering multicast data using so-called overlay networks offers many advantages. Overlay networks only consisting of a multicast group’s members that are connected by means of transport links, non-members (especially routers) no longer need to bother about multicast routing and keeping a group’s state information. While existing application layer multicast protocols mainly were designed for the fixed Internet, first attempts to adapt such protocols for mobile ad-hoc networks start emerging. Because these adaptions however still suffer from a relatively high rate of packet losses, this paper outlines generic mechanisms that improve the overall delivery ratio for application layer multicast protocols. Although the proposed mechanisms are illustrated at the example of the NICE-MAN protocol (which is an adaption of the NICE protocol, originating from the Internet), they may be applied to arbitrary overlays. Furthermore, this paper shows how overlay networks combined with the developed mechanisms can be used, to significantly improve delivery ratios for existing multicast protocols (like ODMRP, M-AODV) that reside on the network layer.

Improving delivery ratios for application layer multicast in mobile ad hoc networks

Delivering multicast data using application layer approaches offers different advantages, as group members communicate using so-called overlay networks. These consist of a multicast groups members connected by unicast tunnels. Since existing approaches for application layer delivery of multicast data in mobile ad hoc networks (short MANETs) only deal with routing but not with error recovery, this paper evaluates tailored mechanisms for handling packet losses and congested networks. Although illustrated at the example of a specific protocol, the mechanisms may be applied to arbitrary overlays. This paper also investigates how application layer functionality based on overlay networks can turn existing multicast routing protocols (like ODMRP, M-AODV,...) into (almost) reliable transport protocols.

Using Linearization for Global Consistency in SSR

Novel routing algorithms such as scalable source routing (SSR) and virtual ring routing (VRR) need to set up and maintain a virtual ring structure among all the nodes in the network. The iterative successor pointer rewiring protocol (ISPRP) is one way to bootstrap such a network. Like its VRR-analogon, ISPRP requires one of the nodes to flood the network to guarantee consistency. Recent results on self-stabilizing algorithms now suggest a new approach to bootstrap the virtual rings of SSR and VRR. This so-called linearization method does not require any flooding at all. Moreover, it has been shown that linearization with shortcut neighbors has on average polylogarithmic convergence time, only.

Towards autonomic networking using overlay routing techniques

With an ever-growing number of computers being embedded into our surroundings, the era of ubiquitous computing is approaching fast. However, as the number of networked devices increases, so does system complexity. Contrary to the goal of achieving an “invisible computer”, the required amount of management and human intervention increases more and more, both slowing down the growth rate and limiting the achievable size of ubiquitous systems. In this paper we present a novel routing approach that is capable of handling complex networks without any administrative intervention. Based on a combination of standard overlay routing techniques and source routes, this approach is capable of efficiently bootstrapping a routable network. Unlike other approaches that try to combine peer-to-peer ideas with ad-hoc networks, sensor networks, or ubiquitous systems, our approach is not based on a routing scheme. This makes the resulting system flexible and powerful with respect at application support as well as efficient with regard to routing overhead and system complexity.