Networked sensors-those that coordinate amongst them-selves to achieve a larger sensing task-will revolutionize information gathering and processing both in urban envi-ronments and in inhospitable terrain. The sheer numbers of these sensors and the expected dynamics in these environ-ments present unique challenges in the design of unattended autonomous sensor networks. These challenges lead us to hypothesize that sensor network coordination applications may need to be structured differently from traditional net-work applications. In particular, we believe that localized algorithms (in which simple local node behavior achieves a desired global objective) may be necessary for sensor net-work coordination. In this paper, we describe localized al-gorithms, and then discuss directed diffusion, a simple com-munication model for describing localized algorithms. 1

The rapid growth of the Web has made it possible to build collaborative applications on an unprecedented scale. However, the request-reply interaction model of HTTP limits the range of applications that can be built. In this paper, we consider a complementary communication model---asynchronous event notification from servers to clients. Our focus in the paper is the design of an Internet-scale mechanism for event dissemination. Such a mechanism must scale to large numbers of participants and event types, as well as provide failure detection and handling. In this paper, we explore the design space of event dissemination architectures, and present a design of a hierarchical proxy architecture for event dissemination. Compared with previous approaches, our design reduces proxy states and provides failure detection and recovery mechanisms. Keywords: event service, collaboration, web, proxy hierarchy I. INTRODUCTION The phenomenal growth of the Web during the past years has made it possible...

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Reliable multicast protocols on top of the MBone are presently subject to intensive research. In the past, numerous protocols have been developed and their respective performance been analysed. Little progress has been made, though, to compare different approaches. In this paper, we use the network simulator ns-2 to evaluate the performance of three protocols, namely Scalable Reliable Multicast (SRM), Multicast File Transfer Protocol (MFTP) and an enhanced version of the latter, called Multicast File Transfer Protocol with Erasure Correction (MFTP/EC). We also compare the results to each other and test the suitability for multicast file distribution. Keywords: Reliable Multicast, Network Simulator, Scalability 1 Introduction Protocols for the reliable one-to-many data transfer can be constructed in various ways, and existing protocol architectures in fact use completely different techniques. As a consequence, they differ in bandwidth consumption and quality of service they offer to t...

Hierarchies have been widely used in computer networks to help systems scale better by reducing or localizing information propagation thereby reducing message and state overhead in the network. However, simple static configuration techniques widely in use today are not robust enough for dynamic environments. In this thesis, we explore the design and evaluation of distributed automatic hierarchy construction techniques for large dynamic networks. We present a taxonomy of approaches and discuss the various components of automatic hierarchy construction techniques. We then present automatic hierarchy construction algorithms for two different environments. Our first algorithm is intended for the Internet while our second application is in the area of networked embedded devices. These two environments differ in the size of the networks, capabilities of the nodes that form the network as well as the type and frequency of network dynamics. Hence the algorithms designed for these two...

Multicast distribution trees usually have multiple bottleneck links. Because of different bottleneck links, multicast users usually experience different receiving rate or packet loss characteristics. A multicast sender faces new challenges of how to handle different users. One solution is to cluster users into separate subgroups. Each subgroup will find a nearby user, called helper, to relay the content at later time, to transcode the content at lower rate, or to repair loss packets. We proposed to cluster users around the common helper. We applied an advertising algorithm for users to find the nearest helper. Such advertising algorithm required users exchange advertisement messages with each other. To avoid high control overhead, we introduce a novel scope controlled advertising algorithm to effectively control the scope of advertisement messages. Our simulation results showed that the traffic injected into network can be greatly reduced for over 50% in some cases. The control traffic...