M.R. van Steen

TRIBLER: a social-based peer-to-peer system

Most current peer‐to‐peer (P2P) file‐sharing systems treat their users as anonymous, unrelated entities, and completely disregard any social relationships between them. However, social phenomena such as friendship and the existence of communities of users with similar tastes or interests may well be exploited in such systems in order to increase their usability and performance. In this paper we present a novel social‐based P2P file‐sharing paradigm that exploits social phenomena by maintaining social networks and using these in content discovery, content recommendation, and downloading. Based on this paradigms main concepts such as taste buddies and friends, we have designed and implemented the TRIBLER P2P file‐sharing system as a set of extensions to BitTorrent. We present and discuss the design of TRIBLER, and we show evidence that TRIBLER enables fast content discovery and recommendation at a low additional overhead, and a significant improvement in download performance. Copyright

Globe: a wide area distributed system

The authors present an object-based framework for developing wide-area distributed applications. The World Wide Webs current performance problems illustrate the benefit of encapsulating state, operations, and implementation strategies on a per-object basis. The authors describe how distributed objects can implement worldwide scalable Web documents.

Locating objects in wide-area systems

Locating mobile objects in a worldwide system requires a scalable location service. An object can be a telephone or a notebook computer, but also a software or data object, such as a file or an electronic document. Our service strictly separates an objects name from the addresses where it can be contacted. This is done by introducing a location-independent object handle. An objects name is bound to its unique object handle, which, in turn, is mapped to the addresses where the object can be contacted. To locate an object, we need only its object handle. We present a scalable location service based on a worldwide distributed search tree that adapts dynamically to an objects migration pattern to optimize lookups and updates.

Globule: a collaborative content delivery network

We present Globule, a collaborative content delivery network developed by our research group. Globule is composed of Web servers that cooperate across a wide area network to provide performance and availability guarantees to the sites they host. We discuss the issues involved in developing and setting up a large-scale collaborative CDN and provide solutions for many of its unique problems

Dynamically selecting optimal distribution strategies for Web documents

To improve the scalability of the Web, it is common practice to apply caching and replication techniques. Numerous strategies for placing and maintaining multiple copies of Web documents at several sites have been proposed. These approaches essentially apply a global strategy by which a single family of protocols is used to choose replication sites and keep copies mutually consistent. We propose a more flexible approach by allowing each distributed document to have its own associated strategy. We propose a method for assigning an optimal strategy to each document separately and prove that it generates a family of optimal results. Using trace-based simulations, we show that optimal assignments clearly outperform any global strategy. We have designed an architecture for supporting documents that can dynamically select their optimal strategy and evaluate its feasibility.

Supporting internet-scale multi-agent systems

The Internet provides a large-scale environment for (intelligent) software agents. Agents are autonomous (mobile) processes, capable of communication with other agents, interaction with the world, and adaptation to changes in their environment. Current approaches to support agents are not geared for large-scale settings. The near future holds thousands of agents, hosts, messages, and migratory movements of agents. These large-scale aspects require a new approach to facilitate the development of agent applications and support. AgentScape is a scalable agent-based distributed system, described in this paper, that aims at tackling these aspects.

2Fast : Collaborative Downloads in P2P Networks

P2P systems that rely on the voluntary contribution of bandwidth by the individual peers may suffer from free riding. To address this problem, mechanisms enforcing fairness in bandwidth sharing have been designed, usually by limiting the download bandwidth to the available upload bandwidth. As in real environments the latter is much smaller than the former, these mechanisms severely affect the download performance of most peers. In this paper we propose a system called 2Fast, which solves this problem while preserving the fairness of bandwidth sharing. In 2Fast, we form groups of peers that collaborate in downloading a file on behalf of a single group member, which can thus use its full download bandwidth. A peer in our system can use its currently idle bandwidth to help other peers in their ongoing downloads, and get in return help during its own downloads. We assess the performance of 2Fast analytically and experimentally, the latter in both real and simulated environments. We find that in realistic bandwidth limit settings, 2Fast improves the download speed by up to a factor of 3.5 in comparison to state-of-the-art P2P download protocols

Latency-driven replica placement

This paper presents HotZone, an algorithm to place replicas in a wide-area network such that the client-to-replica latency is minimized. Similar to the previously proposed HotSpot algorithm, HotZone places replicas on nodes that along with their neighboring nodes generate the highest load. In contrast to HotSpot, however, HotZone provides nearly-optimal results by considering overlapping neighborhoods. HotZone relies on a geometric model of Internet latencies, which effectively reduces the cost of placing K replicas among N potential replica locations from O(N/sup 2/) to O(N /spl middot/ max(logN, K)).

Differentiated strategies for replicating Web documents

Replicating Web documents reduces user-perceived delays and wide-area network traffic. Numerous caching and replication protocols have been proposed to manage such replication while keeping the document copies consistent. We claim, however, that no single caching or replication policy can efficiently manage all documents. Instead, we propose that each document be replicated with a policy specifically tailored to it. We have collected traces on our universitys Web server and conducted simulations to determine the performance such tailored policies would produce, as opposed to using the same policy for all documents. The results show a significant performance improvement with respect to end-user delays, wide-area network traffic and document consistency. We also present how these results can be used to build adaptive replicated Web documents, capable of automatically selecting the policy that best suits them.

A law-abiding peer-to-peer network for free-software distribution

The Globe Distribution Network (GDN) is an application for worldwide distribution of freely redistributable software packages. The GDN takes a novel, optimistic approach to stop the illegal distribution of copyrighted and illicit material via the network. Instead of having moderators check the software archives at upload time, illegal content is removed and its uploaders access to the network permanently revoked only when the content is discovered. An important feature of the GDN is that the objects containing the software can run on untrustworthy servers. A first version of the GDN has been implemented and has been running since October 2000 across four European sites.