In many distributed-memory parallel computers and high-speed communication networks, the exact structure of the underlying communication network may be ignored. These systems assume that the network creates a complete communication graph between the processors, in which passing messages is associated with communication latencies. In this paper, we explore the impact of communication latencies on the design of broadcasting algorithms for fully-connected message-passing systems. For this purpose, we introduce the postal model that incorporates a communication latency parameter 1. This parameter measures the inverse of the ratio between the time it takes an originator of a message to send the message and the time that passes until the recipient of the message receives it. We present an optimal algorithm for broadcasting one message in systems with n processors and communication latency , the running time of which is \Theta( log n log(+1) ). For broadcasting m 1 messages, we first e...

(PRM): a multicast data recovery scheme that improves data delivery ratios while maintaining low end-to-end latencies. PRM has both a proactive and a reactive components; in this paper we describe how PRM can be used to improve the performance of application-layer multicast protocols especially when there are high packet losses and host failures. Through detailed analysis in this paper, we show that this loss recovery technique has efficient scaling properties—the overheads at each overlay node asymptotically decrease to zero with increasing group sizes. As a detailed case study, we show how PRM can be applied to the NICE application-layer multicast protocol. We present detailed simulations of the PRM-enhanced NICE protocol for 10 000 node Internet-like topologies. Simulations show that PRM achieves a high delivery ratio ( 97%) with a low latency bound (600 ms) for environments with high end-to-end network losses (1%–5%) and high topology change rates (5 changes per second) while incurring very low overheads ( 5%). Index Terms—Multicast, networks, overlays, probabilistic forwarding, protocols, resilience. I.

this article follows the aims stated above. The first section introduces this research area. The basic definitions are given and the fundamental, simple observations concerning the relations among the complexity measures defined are carefully explained. This section is

Some forms of ad-hoc networks need to operate in extremely performance-challenged environments where end-to-end connectivity is rare. Such environments can be found for example in very sparse mobile networks where nodes ”meet ” only occasionally and are able to exchange information, or in wireless sensor networks where nodes sleep most of the time to conserve energy. Forwarding mechanisms in such networks usually resort to some form of intelligent flooding, as for example in probabilistic routing. We propose a communication algorithm that significantly reduces the overhead of probabilistic routing algorithms, making it a suitable building block for a delay-tolerant network architecture. Our forwarding scheme is based on network coding. Nodes do not simply forward packets they overhear but may send out information that is coded over the contents of several packets they received. We show by simulation that this algorithm achieves the reliability and robustness of flooding at a small fraction of the overhead.

Abstract—We present efficient algorithms for two all-to-all communication operations in message-passing systems: index (or all-toall personalized communication) and concatenation (or all-to-all broadcast). We assume a model of a fully connected messagepassing system, in which the performance of any point-to-point communication is independent of the sender-receiver pair. We also assume that each processor has k ≥ 1 ports, through which it can send and receive k messages in every communication round. The complexity measures we use are independent of the particular system topology and are based on the communication start-up time, and on the communication bandwidth. In the index operation among n processors, initially, each processor has n blocks of data, and the goal is to exchange the i th block of processor j with the j th block of processor i. We present a class of index algorithms that is designed for all values of n and that features a trade-off between the communication start-up time and the data transfer time. This class of algorithms includes two special cases: an algorithm that is optimal with respect to the measure of the start-up time, and an algorithm that is optimal with respect to the measure of the data transfer time. We also present experimental results featuring the performance tuneability of our index algorithms on the IBM SP-1 parallel system. In the concatenation operation, among n processors, initially, each processor has one block of data, and the goal is to concatenate the n blocks of data from the n processors, and to make the concatenation result known to all the processors. We present a concatenation algorithm that is optimal, for most values of n, in the number of communication rounds and in the amount of data transferred. Index Terms—All-to-all broadcast, all-to-all personalized communication, complete exchange, concatenation operation, distributedmemory system, index operation, message-passing system, multiscatter/gather, parallel system.

Abstract — Epidemic algorithms have been recently recognized as robust and scalable means to disseminate information in large-scale settings. Information is disseminated reliably in a distributed system the same way an epidemic would be propagated throughout a group of individuals: each process of the system chooses random peers to whom it relays the information it has received. The underlying peer-to-peer communication paradigm is the key to the scalability of the dissemination scheme. Epidemic algorithms have been studied theoretically and their analysis is built on sound mathematical foundations. Although promising, their general applicability to large scale distributed systems has yet to go through addressing many issues. These constitute an exciting research agenda. Index Terms — Scalability, peer-to-peer, epidemics, information

In heterogeneous networks, sending messages may incur different delays on different links, and each node may have a different switching time between messages. The well studied Telephone model is obtained when all link delays and switching times are equal to one unit. We investigate the problem of finding the minimum time required to multicast a message from one source to a subset of the nodes of size k. The problem is NP-hard even in the basic Telephone model. We present a polynomial time algorithm that approximates the minimum multicast time within a factor of O(log k). Our algorithm improves on the best known approximation factor for the Telephone model by a factor of O log n log log k . No approximation algorithms were known for the general model considered in this paper.

The dissertation presents the issues addressed in the design of Ficus, a large scale wide area distributed file system currently operational on a modest scale at UCLA. Key aspects of providing such a service include toleration of partial operation in virtually all areas; support for large scale, optimistic data replication; and a flexible, extensible modular design. Ficus incorporates a "stackable layers" modular architecture and full support for optimistic replication. Replication is provided by a pair of layers operating in concert above a traditional filing service. A "volume" abstraction and on-the-fly volume "grafting" mechanism are used to manage the large scale file name space. The replication service uses a f...

This paper studies the problems of broadcasting and gossiping in optical networks. In such networks the vast bandwidth available is utilized through wavelength division multiplexing: a single physical optical link can carry several logical signals, provided that they are transmitted on different wavelengths. In this paper we consider both single--hop and multihop optical networks. In single--hop networks the information, once transmitted as light, reaches its destination without being converted to electronic form in between, thus reaching high speed communication. In multi hop networks a packet may have to be routed through a few intermediate nodes before reaching its final destination. In both models, we give efficient broadcasting and gossiping algorithms, in terms of time and number of wavelengths. We consider both networks with arbitrary topologies and particular networks of practical interest. Several of our algorithms exhibit optimal performances. 1 Introduction Motivations. Op...

We consider the following basic communication problems in a hypercube network of processors: the problem of a single processor sending a different packet to each of the other processors, the problem of simultaneous broadcast of the same packet from every processor to all other processors, and the problem of simultaneous exchange of different packets between every pair of processors. The algorithms proposed for these problems are optimal in terms of execution time and communication resource requirements; that is, they require the minimum possible number of time steps and packet transmissions. In contrast, algorithms in the literature are optimal only within an additive or multiplicative factor. @ 1991 Academic Press,lnc. 263 to the coordinates of a node of the d-cube is referred to as the identity number of the node. We recall that a hypercube of any dimension can be constructed by connecting lowerdimensional cubes, starting with a l-cube. In particular, we can start with two (d-I)-dimensional cubes and introduce a link connecting each pair of nodes with the same identity number (see, e.g., [I, Sect. 1.3]). This constructs ad-cube with the identity number of each node obtained by adding a leading 0 or a leading I to its previous identity, depending on whether the node belongs to the first (d-I)-dimensional cube or the second (see Fig. I). When confusion cannot arise, we refer to a d-cube node interchangeably in terms of its identity number (a binary string of length d) and in terms of the decimal representation of its identity number. Thus,