We present Tapestry, a peer-to-peer overlay routing infrastructure offering efficient, scalable, locationindependent routing of messages directly to nearby copies of an object or service using only localized resources. Tapestry supports a generic Decentralized Object Location and Routing (DOLR) API using a self-repairing, softstate based routing layer. This paper presents the Tapestry architecture, algorithms, and implementation. It explores the behavior of a Tapestry deployment on PlanetLab, a global testbed of approximately 100 machines. Experimental results show that Tapestry exhibits stable behavior and performance as an overlay, despite the instability of the underlying network layers. Several widely-distributed applications have been implemented on Tapestry, illustrating its utility as a deployment infrastructure.

Large-scale distributed systems are hard to deploy, and distributed hash tables (DHTs) are no exception. To lower the barriers facing DHT-based applications, we have created a public DHT service called OpenDHT. Designing a DHT that can be widely shared, both among mutually untrusting clients and among a variety of applications, poses two distinct challenges. First, there must be adequate control over storage allocation so that greedy or malicious clients do not use more than their fair share. Second, the interface to the DHT should make it easy to write simple clients, yet be sufficiently general to meet a broad spectrum of application requirements. In this paper we describe our solutions to these design challenges. We also report our early deployment experience with OpenDHT and describe the variety of applications already using the system.

We describe the design and implementation of SWORD, a scalable resource discovery service for wide-area distributed systems. In contrast to previous systems, SWORD allows users to describe desired resources as a topology of interconnected groups with required intra-group, inter-group, and per-node characteristics, along with the utility that the application derives from specified ranges of metric values. This design gives users the flexibility to find geographically distributed resources for applications that are sensitive to both node and network characteristics, and allows the system to rank acceptable configurations based on their quality for that application. Rather than evaluating a single implementation of SWORD, we explore a variety of architectural designs that deliver the required functionality in a scalable and highly-available manner. We discuss the tradeoffs of using a centralized architecture as compared to a fully decentralized design to perform wide-area resource discovery. To summarize our results, we found that a centralized architecture based on 4-node server cluster sites at network peering facilities outperforms a decentralized DHT-based resource discovery infrastructure with respect to query latency for all but the smallest number of sites. However, although a centralized architecture shows significant promise in stable environments, we find that our decentralized implementation has acceptable performance and also benefits from the DHT’s self-healing properties in more volatile environments. We evaluate the advantages and disadvantages of centralized and distributed resource discovery architectures on 1000 hosts in emulation and on approximately 200 PlanetLab nodes spread across the Internet.

Anonymous routing protects user communication from identification by third-party observers. Existing anonymous routing layers utilize Chaum-Mixes for anonymity by relaying traffic through relay nodes called mixes. The source defines a static forwarding path through which traffic is relayed to the destination. The resulting path is fragile and shortlived: failure of one mix in the path breaks the forwarding path and results in data loss and jitter before a new path is constructed. In this paper, we propose Cashmere, a resilient anonymous routing layer built on a structured peer-to-peer overlay. Instead of single-node mixes, Cashmere selects regions in the overlay namespace as mixes. Any node in a region can act as the MIX, drastically reducing the probability of a mix failure. We analyze Cashmere’s anonymity and measure its performance through simulation and measurements, and show that it maintains high anonymity while providing orders of magnitude improvement in resilience to network dynamics and node failures. 1

A `second generation' approach to the provision of Grid middleware is now emerging which is built on service-oriented architecture and web services standards and technologies. However, advanced Grid applications have significant demands that are not addressed by present-day web services platforms. As one prime example, current platforms do not support the rich diversity of communication `interaction types' that are demanded by advanced applications (e.g. publish-subscribe, media streaming, peer-to-peer interaction).

Structured peer-to-peer overlays provide a natural infrastructure for resilient routing via efficient fault detection and precomputation of backup paths. These overlays can respond to faults in a few hundred milliseconds by rapidly shifting between alternate routes. In this paper, we present two adaptive mechanisms for structured overlays and illustrate their operation in the context of Tapestry, a fault-resilient overlay from Berkeley. We also describe a transparent, protocol-independent traffic redirection mechanism that tunnels legacy application traffic through overlays. Our measurements of a Tapestry prototype show it to be a highly responsive routing service, effective at circumventing a range of failures while incurring reasonable cost in maintenance bandwidth and additional routing latency.

Structured peer-to-peer overlay networks are now an established paradigm for implementing a wide range of distributed services. While the problem of maintaining these networks in the presence of churn and other failures is the subject of intensive research, the problem of building them from scratch has not been addressed (apart from individual nodes joining an already functioning overlay). In this paper we address the problem of jump-starting a popular structured overlay, Chord, from scratch. This problem is of crucial importance in scenarios where one is assigned a limited time interval in a distributed environment such as Planet-Lab, or a Grid, and the overlay infrastructure needs to be set up from the ground up as quickly and efficiently as possible, or when a temporary overlay has to be generated to solve a specific task on demand. We introduce T-CHORD, that can build a Chord network efficiently starting from a random unstructured overlay. After jump-starting, the structured overlay can be handed over to the Chord protocol for further maintenance. We demonstrate through extensive simulation experiments that the proposed protocol can create a perfect Chord topology in a logarithmic number of steps. Furthermore, using a simple extension of the protocol, we can optimize the network from the point of view of message latency. 1.

Abstract. Next-generation Grid applications will be highly heterogeneous in nature, will run on many types of computer and device, will operate within and across many heterogeneous network types, and must be explicitly configurable and runtime reconfigurable. We refer to this future Grid environment as the “divergent Grid”. In this paper, we propose a “deep middleware ” approach to meeting key requirements of the divergent Grid. Deep middleware reaches down into the network to provide highly flexible network support that underpins a rich, extensible and reconfigurable set of application-level “interaction paradigms ” (such as publish-subscribe, multicast, tuple spaces etc.). In our Gridkit middleware platform, these facilities are encapsulated in two key component frameworks: the interaction framework and the overlay framework, which are the subject of this paper. The paper also evaluates the two frameworks in terms of their configurability (e.g. ability to be profiled for different device types) and reconfigurability (e.g. to self-optimise as the environment changes). 1

Abstract — We study the scalable management of XML data in P2P networks based on distributed hash tables (DHTs). We identify performance limitations in this context, and propose an array of techniques to lift them. First, we adapt the DHT platform’s index store and communication primitives to the needs of massive data processing. Second, we introduce a distributed hierarchical index and associated efficient algorithms to speed up query processing. Third, we present an innovative, XMLspecific flavor of Bloom filters, to reduce data transfers entailed by query processing. Our approach is fully implemented in the KadoP system, used in a real-life software manufacturing application. Our experiments demonstrate the benefits of the proposed techniques. I.

In order to provide an increasing number of functionalities and benefit from sophisticated and application-tailored services from the network, distributed applications are led to integrate an everwidening range of networking technologies. As these applications become more complex, this requirement for ‘network heterogeneity ’ is becoming a crucial issue in their development. Although progress has been made in the networking community in addressing such needs through the development of network overlays, we claim in this paper that the middleware community has been slow to integrate these advances into middleware architectures, and, hence, to provide the foundational bedrock for heterogeneous distributed applications. In response, we propose our ‘open overlays ’ framework. This framework, which is part of a wider middleware architecture, accommodates ‘overlay plugins’, allows physical nodes to support multiple overlays, supports the stacking of overlays to create composite protocols, and adopts a declarative approach to configurable deployment and dynamic reconfigurability. The framework has been in development for a number of years and supports an extensive range of overlay plugins including popular protocols such as Chord and Pastry. We report on our experiences with the open overlays framework, evaluate it in detail, and illustrate its application in a detailed case study of network heterogeneity.