993 research outputs found
Vitis: A Gossip-based Hybrid Overlay for Internet-scale Publish/Subscribe
Peer-to-peer overlay networks are attractive solutions for building Internet-scale publish/subscribe systems. However, scalability comes with a cost: a message published on a certain topic often needs to traverse a large number of uninterested (unsubscribed) nodes before reaching all its
subscribers. This might sharply increase resource consumption for such relay nodes (in terms of bandwidth transmission cost, CPU, etc) and could ultimately lead to rapid deterioration of the system’s performance once the relay nodes start dropping the messages or choose to permanently abandon the system. In this paper, we introduce Vitis, a gossip-based publish/subscribe system that significantly decreases the number of relay messages, and scales to an unbounded number of nodes and topics. This is achieved by the novel approach of enabling rendezvous routing on unstructured overlays. We construct a hybrid system by injecting structure into an otherwise unstructured network. The resulting structure resembles a navigable small-world network, which spans along clusters of nodes that have similar subscriptions. The properties of such an overlay make it an ideal platform for efficient data dissemination in large-scale systems. We perform extensive simulations and evaluate Vitis by comparing its performance against two base-line publish/subscribe systems: one that is oblivious to node subscriptions, and another that exploits the subscription similarities. Our measurements show that Vitis significantly outperforms the base-line solutions on various subscription and churn scenarios, from both synthetic models and real-world traces
Handling Network Partitions and Mergers in Structured Overlay Networks
Structured overlay networks form a major class of peer-to-peer systems, which are touted for their abilities to
scale, tolerate failures, and self-manage. Any long-lived
Internet-scale distributed system is destined to face network partitions. Although the problem of network partitions
and mergers is highly related to fault-tolerance and
self-management in large-scale systems, it has hardly been
studied in the context of structured peer-to-peer systems.
These systems have mainly been studied under churn (frequent
joins/failures), which as a side effect solves the problem
of network partitions, as it is similar to massive node
failures. Yet, the crucial aspect of network mergers has been
ignored. In fact, it has been claimed that ring-based structured
overlay networks, which constitute the majority of the
structured overlays, are intrinsically ill-suited for merging
rings. In this paper, we present an algorithm for merging
multiple similar ring-based overlays when the underlying
network merges. We examine the solution in dynamic conditions,
showing how our solution is resilient to churn during
the merger, something widely believed to be difficult or
impossible. We evaluate the algorithm for various scenarios
and show that even when falsely detecting a merger, the
algorithm quickly terminates and does not clutter the network
with many messages. The algorithm is flexible as the
tradeoff between message complexity and time complexity
can be adjusted by a parameter
A Lightweight Approach for Improving the Lookup Performance in Kademlia-type Systems
Discovery of nodes and content in large-scale distributed systems is
generally based on Kademlia, today. Understanding Kademlia-type systems to
improve their performance is essential for maintaining a high service quality
for an increased number of participants, particularly when those systems are
adopted by latency-sensitive applications.
This paper contributes to the understanding of Kademlia by studying the
impact of \emph{diversifying} neighbours' identifiers within each routing table
bucket on the lookup performance. We propose a new, yet backward-compatible,
neighbour selection scheme that attempts to maximize the aforementioned
diversity. The scheme does not cause additional overhead except negligible
computations for comparing the diversity of identifiers. We present a
theoretical model for the actual impact of the new scheme on the lookup's hop
count and validate it against simulations of three exemplary Kademlia-type
systems. We also measure the performance gain enabled by a partial deployment
for the scheme in the real KAD system. The results confirm the superiority of
the systems that incorporate our scheme.Comment: 13 pages, 8 figures, conference version 'Diversity Entails
Improvement: A new Neighbour Selection Scheme for Kademlia-type Systems' at
IEEE P2P 201
An analytical framework for the performance evaluation of proximity-aware structured overlays
In this paper, we present an analytical study of proximity-aware structured peer-to-peer networks under churn. We use a master-equation-based approach, which is used traditionally in non-equilibrium statistical mechanics to describe steady-state or transient phenomena. In earlier work we have demonstrated that this methodology is in fact also well suited to describing structured overlay networks under churn, by showing how we can accurately predict the average number of hops taken by a lookup, for any value of churn, for the Chord system. In this paper, we extend the analysis so as to also be able to predict lookup latency, given an average latency for the links in the network. Our results show that there exists a region in the parameter space of the model, depending on churn, the number of nodes, the maintenance rates and the delays in the network, when the network cannot function as a small world graph anymore, due to the farthest connections of a node always being wrong or dead. We also demonstrate how it is possible to analyse proximity neighbour selection or proximity route selection within this formalism
Considering Complex Search Techniques in DHTs Under Churn
Abstract-Traditionally complex queries have been performed over unstructured P2P networks by means of flooding, which is inherently inefficient due to the large number of redundant messages generated. While Distributed Hash Tables (DHTs) can provide very efficient look-up operations, they traditionally do not provide any methods for complex queries. By exploiting the structure inherent in DHTs we can perform complex querying over structured P2P networks by means of efficiently broadcasting the search query. This allows every node in the network to process the query locally, and hence is as powerful and flexible as flooding in unstructured networks, but without the inefficiency of redundant messages. While there have been various approaches proposed for broadcasting search queries over DHTs, the focus has not been on validation under churn. Comparing blind search methods for DHTs through simulation we see that churn, in particular nodes leaving the network, has a large impact on query success rate. In this paper we present novel results comparing blind search over Chord and Pastry while under varying levels of churn. We further consider how different data replication strategies can be used to enhance the query success rate
Broadcasting in Prefix Space: P2P Data Dissemination with Predictable Performance
A broadcast mode may augment peer-to-peer overlay networks with an efficient,
scalable data replication function, but may also give rise to a virtual link
layer in VPN-type solutions. We introduce a simple broadcasting mechanism that
operates in the prefix space of distributed hash tables without signaling. This
paper concentrates on the performance analysis of the prefix flooding scheme.
Starting from simple models of recursive -ary trees, we analytically derive
distributions of hop counts and the replication load. Extensive simulation
results are presented further on, based on an implementation within the OverSim
framework. Comparisons are drawn to Scribe, taken as a general reference model
for group communication according to the shared, rendezvous-point-centered
distribution paradigm. The prefix flooding scheme thereby confirmed its widely
predictable performance and consistently outperformed Scribe in all metrics.
Reverse path selection in overlays is identified as a major cause of
performance degradation.Comment: final version for ICIW'0
Performance analysis of structured peer-to-peer overlays for mobile networks
Distributed Hash Table (DHT) based Peer-to-Peer (P2P) overlays have been widely researched and deployed in many applications such as file sharing, IP telephony, content distribution and media streaming applications. However, their deployment has largely been restricted to fixed, wired networks. This is due to the fact that supporting P2P overlays on wireless networks such as the public mobile data network is more challenging due to constraints in terms of data transmissions on cellular networks, limited battery power of the handsets and increased levels of node churn. However, the proliferation of smartphones makes the use of P2P applications on mobile handsets very desirable. In this paper, we have analysed and evaluated the performance and efficiency of five popular DHT based structured P2P overlays (Chord, Pastry, Kademlia, Broose and EpiChord) under conditions as commonly experienced in public mobile data networks. Our results show that the conditions in mobile networks, including a high churn rate and the relatively low bandwidth availability is best matched by Kademlia and EpiChord. These overlays exhibit a high lookup success ratio and low hop count while consuming a moderate amount of bandwidth. These characteristics make these two overlays suitable candidates for use in mobile networks
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