Araneola: A scalable reliable multicast system for dynamic environments

Abstract

This paper presents Araneola (Araneola means "little spider" in Latin.), a scalable reliable application-level multicast system for highly dynamic wide-area environments. Araneola supports multi-point to multi-point reliable communication in a fully distributed manner, while incurring constant load (in terms of message and space complexity) on each node. For a tunable parameter k ≥ 3, Araneola constructs and dynamically maintains a basic overlay structure in which each node's degree is either k or k + 1, and roughly 90% of the nodes have degree k. Empirical evaluation shows that Araneola's basic overlay achieves three important mathematical properties of k-regular random graphs (i.e., random graphs in which each node has exactly k neighbors) with N nodes: (i) its diameter grows logarithmically with N; (ii) it is generally k-connected; and (iii) it remains highly connected following random removal of linear-size subsets of edges or nodes. The overlay is constructed and maintained at a low cost: each join, leave, or failure is handled locally, and entails the sending of only about 3 k messages in total, independent of N. Moreover, this cost decreases as the churn rate increases. The low degree of Araneola's basic overlay structure allows for allocating plenty of additional bandwidth for specific application needs. In this paper, we give an example for such a need - communicating with nearby nodes; we enhance the basic overlay with additional links chosen according to geographic proximity and available bandwidth. We show that this approach, i.e., a combination of random and nearby links, reduces the number of physical hops messages traverse without hurting the overlay's robustness, as compared with completely random Araneola overlays (in which all the links are random) with the same average node degree. Given Araneola's overlay, we sketch out several message dissemination techniques that can be implemented on top of this overlay. We present a full implementation and evaluation of a gossip-based multicast scheme, with up to 10,000 nodes. We show that compared with a (non-overlay-based) gossip-based multicast protocol, gossiping over Araneola achieves substantial improvements in load, reliability, and latency. © 2008 Elsevier Inc. All rights reserved.