This paper examines graph-theoretic properties of existing peer-to-peer architectures and proposes a new infrastructure based on optimal-diameter de Bruijn graphs. Since generalized de Bruijn graphs possess very short average routing distances and high resilience to node failure, they are well suited for structured peer-to-peer networks. Using the example of Chord, CAN, and de Bruijn, we first study routing performance, graph expansion, and clustering properties of each graph. We then examine bisection width, path overlap, and several other properties that affect routing and resilience of peer-to-peer networks. Having confirmed that de Bruijn graphs offer the best diameter and highest connectivity among the existing peer-to-peer structures, we offer a very simple incremental building process that preserves optimal properties of de Bruijn graphs under uniform user joins/departures. We call the combined peer-to-peer architecture

Currently the Internet has only one level of name resolution, DNS, which converts user-level domain names into IP addresses. In this paper we borrow liberally from the literature to argue that there should be three levels of name resolution: from user-level descriptors to service identifiers; from service identifiers to endpoint identifiers; and from endpoint identifiers to IP addresses. These additional levels of naming and resolution (1) allow services and data to be first class Internet objects and (2) facilitate mobility and provide an elegant way to integrate middleboxes into the Internet architecture. We further argue that flat names are a natural choice for the service and endpoint identifiers. Hence, this architecture requires scalable resolution of flat names, a capability that distributed hash tables (DHTs) can provide.

Abstract — Most P2P systems that provide a DHT abstraction distribute objects randomly among “peer nodes ” in a way that results in some nodes having times as many objects as the average node. Further imbalance may result due to nonuniform distribution of objects in the identifier space and a high degree of heterogeneity in object loads and node capacities. Additionally, a node’s load may vary greatly over time since the system can be expected to experience continuous insertions and deletions of objects, skewed object arrival patterns, and continuous arrival and departure of nodes. In this paper, we propose an algorithm for load balancing in such heterogeneous, dynamic P2P systems. Our simulation results show that in the face of rapid arrivals and departures of objects of widely varying load, our algorithm achieves load balancing for system utilizations as high as 90 % while moving only about 8 % of the load that arrives into the system. Similarly, in a dynamic system where nodes arrive and depart, our algorithm moves less than 60 % of the load the underlying DHT moves due to node arrivals and departures. Finally, we show that our distributed algorithm performs only negligibly worse than a similar centralized algorithm, and that node heterogeneity helps, not hurts, the scalability of our algorithm. I.

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We study the problem of routing in doubling metrics, and show how to perform hierarchical routing in such metrics with small stretch and compact routing tables (i.e., with small amount of routing information stored at each vertex). We say that a metric (X, d) has doubling dimension dim(X) at most α if every set of diameter D can be covered by 2 α sets of diameter D/2. (A doubling metric is one whose doubling dimension dim(X) is a constant.) We show how to perform (1 + τ)-stretch routing on metrics for any 0 < τ ≤ 1 with routing tables of size at most (α/τ) O(α) log 2 ∆ bits with only (α/τ) O(α) log ∆ entries, where ∆ is the diameter of the graph; hence the number of routing table entries is just τ −O(1) log ∆ for doubling metrics. These results extend and improve on those of Talwar (2004). We also give better constructions of sparse spanners for doubling metrics than those obtained from the routing tables above; for τ> 0, we give algorithms to construct (1 + τ)stretch spanners for a metric (X, d) with maximum degree at most (2 + 1/τ) O(dim(X)) , matching the results of Das et al. for Euclidean metrics.

Micah Adler # Department of Computer Science, University of Massachusetts, Amherst, MA 01003-4610, USA micah@cs.umass.edu Eran Halperin + Science Institute and Computer Science Division University of California Berkeley, CA 94720.

A content-addressable network (CAN) is a distributed lookup table that can be used to implement peer-to-peer (P2P) systems. A CAN allows the discovery and location of data and/or resources, identi ed by keys, in a distributed network (e.g., Internet), in absence of centralized server or any hierarchical organization. Several networks have been recently described in the literature, and some of them have led to the development of experimental systems. We present a new CAN, called d2b. Its main characteristics are: simplicity, provability, and scalability. d2b allows the number of nodes n to vary between 1 and jKj where K is the set of keys managed by the network. In term of performances, any join or leave of a user implies a constant expected number of link modi cations, and, with high probability (w.h.p.), at most O(log n) link modi cations.

Routing topologies for distributed hashing in peer-to-peer networks are classified into two categories: deterministic and randomized. A general technique for constructing determin-istic routing topologies is presented. Using this technique, classical parallel interconnection networks can be adapted to handle the dynamic nature of participants in peer-to-peer networks. A unified picture of randomized routing topolo-gies is also presented. Two new protocols are described which improve average latency as a function of out-degree. One of the protocols can be shown to be optimal with high probability. Finally, routing networks for distributed hash-ing are revisited from a systems perspective and several open design problems are listed.

Establishing peer-to-peer (P2P) file sharing for mobile ad hoc networks ANET) requires the construction of a search algorithm for transmitting queries and search results as well as the development of a transfer protocol for downloading files matching a query. In this paper, we present a special-purpose system for searching and file transfer tailored to both the characteristics of MANET and the requirements of peer-to-peer file sharing. Our approach is based on an application layer overlay networlc As innovative feature, overlay routes are set up on demand by the search algorithm, closely matching network topology and transparently aggregating redundant transfer paths on a per-file basis. The transfer protocol guarantees high data rates and low transmission overhead by utilizing overlay routes. In a detailed ns2 simulation study, we show that both the search algorithm and the transfer protocol outperform offthe -shelf approaches based on a P2P file sharing system for the wireline Internet, TCP and a MANET routing protocol.

Distributed Hash Tables have been proposed as flat, nonhierarchical structures, in contrast to most scalable distributed systems of the past. We show how to construct hierarchical DHTs while retaining the homogeneity of load and functionality offered by flat designs. Our generic construction, Canon, offers the same routing state v/s routing hops trade-off provided by standard DHT designs. The advantages of Canon include (but are not limited to) (a) fault isolation, (b) efficient caching and effective bandwidth usage for multicast, (c) adaptation to the underlying physical network, (d) hierarchical storage of content, and (e) hierarchical access control. Canon can be applied to many different proposed DHTs to construct their Canonical versions. We show how four different DHTs—Chord, Symphony, CAN and Kademlia—can be converted into their Canonical versions that we call Crescendo, Cacophony,