This paper presents the design, implementation and performance of a reliable multicast transport protocol called RMTP. RMTP is based on a hierarchical structure in which receivers are grouped into local regions or domains and in each domain there is a special receiver called a Designated Receiver (DR) which is responsible for sending acknowledgments periodically to the sender, for processing acknowledgements from receivers in its domain and for retransmitting lost packets to the corresponding receivers. Since lost packets are recovered by local retransmissions as opposed to retransmissions from the original sender, end-to-end latency is significantly reduced, and the overall throughput is improved as well. Also, since only the DRs send their acknowledgments to the sender, instead of all receivers sending their acknowledgments to the sender, a single acknowledgement is generated per local region, and this prevents acknowledgement implosion. Receivers in RMTP send their acknowledgments to the DRs periodically, thereby simplifying error recovery. In addition, lost packets are recovered by selective repeat retransmissions, leading to improved throughput at the cost of minimal additional buffering at the receivers. This paper also describes the implementation of RMTP and its performance on the Internet.

This paper describes the Player/Stage software tools applied to multi-robot, distributed-robot and sensor network systems. Player is a robot device server that provides network transparent robot control. Player seeks to constrain controller design as little as possible; it is device independent, non-locking and language- and style-neutral. Stage is a lightweight, highly configurable robot simulator that supports large populations. Player/Stage is a community Free Software project. Current usage of Player and Stage is reviewed, and some interesting research opportunities opened up by this infrastructure are identified.

Rapid growth in data volume, user base, and data diversity render Internet-accessible information increasingly difficult to use effectively. In this paper we introduce Harvest, a system that provides an integrated set of customizable tools for gathering information from diverse repositories, building topic-specific content indexes, flexibly searching the indexes, widely replicating them, and caching objects as they are retrieved across the Internet. The system interoperates with WWW clients and with HTTP,FTP, Gopher, and NetNews information resources. We discuss the design and implementation of Harvest and its subsystems, give examples of its uses, and provide measurements indicating that Harvest can significantly reduce server load, network traffic, and space requirements when building indexes, compared with previous systems. We also discuss several popular indexes wehave built using Harvest, underscoring the customizability and scalability of the system.

The volume and complexity of traffic on the Internet is increasing rapidly, making it both more difficult and more important to understand. To this end we have created the CoralReef passive traffic monitoring suite, which can be

We discuss the unique architectural elements of the Los Alamos Message Passing Interface (LA-MPI), a high-performance, network-fault-tolerant, thread-safe MPI library. LA-MPI is designed for use on terascale clusters which are inherently unreliable due to their sheer number of system components and tradeoffs between cost and performance. We examine in detail the design concepts used to implement LA-MPI. These include reliability features, such as applicationlevel checksumming, message retransmission, and automatic message re-routing. Other key performance enhancing features, such as concurrent message routing over multiple, diverse network adapters and protocols, and communication-specific optimizations (e.g., shared memory) are examined. 1

Abstract — We consider the issue of designing a generic transport layer protocol for energy-constrained sensor networks. We present the requirements for such a transport protocol and propose Sensor Transmission Control Protocol (STCP). STCP is a generic, scalable and reliable transport layer protocol where a majority of the functionalities are implemented at the base station. STCP offers controlled variable reliability, congestion detection and avoidance, and supports multiple applications in the same network. We present the design and implementation of STCP and evaluate the protocol with different scenarios and network characteristics. I. REQUIREMENTS OF A GENERIC TRANSPORT LAYER Sensor networks are deployed for a wide range of applications in the military, health, environment, agriculture and office domain. Every application has different characteristics

A Client Oriented, IP Level Redirection Mechanism. (August 1998) Sumit Gupta, B.Tech., Indian Institute of Technology, Kanpur, India Chair of Advisory Committee: Dr. A.L. Narasimha Reddy This thesis introduces a new approach for implementing transparent client access to network services. Ever increasing load on the Internet has made it essential to design services that are fast, reliable, easily manageable, transparent to access, and that can scale gracefully with load. A common way of achieving this has been replicating services across multiple servers and redirecting clients to different servers depending upon various criteria. Existing schemes are either entirely server or network based and have many drawbacks. This scheme involves the client network layer actively in redirection. The thesis describes the redirection protocol in detail and the basic implementation of the testbed. The performance of the mechanism is measured by experiments on the testbed and analyzed. The advantages ...

. As in many other multi-agent applications, most RoboCup agents are complex systems, hard to construct and hard to verify whether they behave as intended. We present a technique to verify multi-agent systems based on inductive reasoning. Induction allows to derive general rules from specific examples (e.g. the inputs and outputs of software systems). Using inductive logic programming, partial declarative specifications of the software can be induced. These rules can be readily interpreted by the designers or users of the software, and can in turn result in changes to the software. The approach outlined was used to test the KULRoT RoboCup simulator team, which is briefly described. 1

Of considerable interest in recent years has been the problem of exchanging correlated data with minimum communication. We thus consider the problem of exchanging two similar strings held by different hosts. Our approach involves transforming a string into a multi-set of substrings that are reconciled efficiently using known multi-set reconciliation algorithms, and then put back together on a remote host using tools from graph theory. We present analyses, experiments and results to show that the communication complexity of our approach for high-entropy data compares favorably to existing algorithms including rsync, a widely-used string reconciliation engine. We also quantify the tradeoff between communication and the computation complexity of our approach. Index Terms efficient file synchronization, string reconstruction, rsync I.

During the past two decades, video coding technology has matured and stat-of-the-art coding standards have become very important part of the video industry. Standards such as MPEG-2 [16] and H.264/AVC [20] provide strong support for digital video transmission, storage and streaming applications. Wireless Communication and Mobile Computing