Object Distribution Networks for World-wide Document Circulation

This paper presents an Object Distribution System (ODS), a distributed system inspired by the ultra-large scale distribution models used in everyday life (e.g. food or newspapers distribution chains). Beyond traditional mechanisms of approaching information to readers (e.g. caching and mirroring), this system enables the publication, classification and subscription to volumes of objects (e.g. documents, events). Authors submit their contents to publication agents. Classification authorities provide classification schemes to classify objects. Readers subscribe to topics or authors, and retrieve contents from their local delivery agent (like a kiosk or library, with local copies of objects). Object distribution is an independent process where objects circulate asynchronously among distribution agents. ODS is designed to perform specially well in an increasingly populated, widespread and complex Internet jungle, using weak consistency replication by object distribution, asynchronous replication, and local access to objects by clients. ODS is based on two independent virtual networks, one dedicated to the distribution (replication) of objects and the other to calculate optimised distribution chains to be applied by the first network

Towards Scalable Web Documents

The current Web is running into serious scalability problems. The standard solution is to apply techniques like caching, replication, and distribution. Unfortunately, as the variety of Web applications continues to grow, it will be impossible to find a single solution that fits all needs. The authors advocate a different approach to tackling scaling problems. Instead of seeking a general-purpose solution, they argue that it makes more sense to look at each Web document separately. For each document, three issues need to be addressed: placement of replicas, required coherence, and best coherence protocol. The authors examine each of these issues, and identify the alternatives. However, forcing developers to decide on the best alternatives will turn the Web into an unworkable system. Therefore, a number of possible ways to reduce complexity is indicated. Also, the authors briefly discuss a wide-area infrastructure that can be used as a flexible basis for developing per-document solutions

Towards an efficient, scalable replication mechanism for the I2-DSI project

This thesis presents the development of new functionality for the open-source rsync utility aimed at producing an efficient, scalable solution for multiple-site file synchronization. The context of our work is the Internet2 Distributed Storage Infrastructure (I2-DSI) project, which is developing a reliable, scalable, high performance storage service infrastructure for advanced applications in research and education. Specifically, the I2-DSI project is working on middleware software to enable the replication of applications across a set of geographically distributed hosts. This thesis presents a new mechanism for replicating filesystems, rsync+, which is a modification of an open-source rsync file synchronization utility. Using rsync+ for file updates, a flexible, powerful replication mechanism can be developed for publishing source objects into the I2-DSI replication service, and the approach enable scalable network distribution through multicast-based solutions. The thesis presents the technical details behind the rsync+ tool, its use as a replication solution within I2-DSI, and performance results from a large-scale (multi-gigabyte) WWW mirroring experiment using rsync+ that demonstrates correct operation and efficiency gains with actual data from an active WWW document archive

A Scalable Middleware Solution for Advanced Wide Area Web Services

To alleviate scalability problems in the Web, many researchers concentrate on how to incorporate advanced caching and replication techniques. Many solutions incorporate object-based techniques. In particular, Web resources are considered as distributed objects offering a well-defined interface. We argue that most proposals ignore two important aspects. First, there is little discussion on what kind of coherence should be provided. Proposing specific caching or replication solutions makes sense only if we know what coherence model they should implement. Second, most proposals treat all Web resources alike. Such a one-size-fits-all approach will never work in a wide-area system. We propose a solution in which Web resources are encapsulated in physically distributed shared objects. Each object should encapsulate not only state and operations, but also the policy by which its state is distributed, cached, replicated, migrated, etc

Internet Protocol (IP) Multicast: Final Report

Report presents the results of the Institute for Simulation and Training\u27s implementation and integration of new protocols into the Testbed for Research in Distributed Interactive Simulation (TRDIS) testbed, especially the Internet Protocol (IP) Multicast (IPmc) and Internet Group Management Protocol network protocols, into a simulation application

Unificación de los protocolos de multipunto fiable optimizando la escalabilidad y el retardo

Las aplicaciones distribuidas que precisan de un servicio multipunto fiable son muy numerosas, y entre otras es posible citar las siguientes: bases de datos distribuidas, sistemas operativos distribuidos, sistemas de simulación interactiva distribuida y aplicaciones de distribución de software, publicaciones o noticias. Aunque en sus orígenes el dominio de aplicación de tales sistemas distribuidos estaba reducido a una única subred (por ejemplo una Red de Área Local) posteriormente ha surgido la necesidad de ampliar su aplicabilidad a interredes. La aproximación tradicional al problema del multipunto fiable en interredes se ha basado principalmente en los dos siguientes puntos: (1) proporcionar en un mismo protocolo muchas garantías de servicio (por ejemplo fiabilidad, atomicidad y ordenación) y a su vez algunas de éstas en distintos grados, sin tener en cuenta que muchas aplicaciones multipunto que precisan fiabilidad no necesitan otras garantías; y (2) extender al entorno multipunto las soluciones ya adoptadas en el entorno punto a punto sin considerar las características diferenciadoras; y de aquí, que se haya tratado de resolver el problema de la fiabilidad multipunto con protocolos extremo a extremo (protocolos de transporte) y utilizando esquemas de recuperación de errores, centralizados (las retransmisiones se hacen desde un único punto, normalmente la fuente) y globales (los paquetes solicitados se vuelven a enviar al grupo completo). En general, estos planteamientos han dado como resultado protocolos que son ineficientes en tiempo de ejecución, tienen problemas de escalabilidad, no hacen un uso óptimo de los recursos de red y no son adecuados para aplicaciones sensibles al retardo. En esta Tesis se investiga el problema de la fiabilidad multipunto en interredes operando en modo datagrama y se presenta una forma novedosa de enfocar el problema: es más óptimo resolver el problema de la fiabilidad multipunto a nivel de red y separar la fiabilidad de otras garantías de servicio, que pueden ser proporcionadas por un protocolo de nivel superior o por la propia aplicación. Siguiendo este nuevo enfoque se ha diseñado un protocolo multipunto fiable que opera a nivel de red (denominado RMNP). Las características más representativas del RMNP son las siguientes; (1) sigue una aproximación orientada al emisor, lo cual permite lograr un grado muy alto de fiabilidad; (2) plantea un esquema de recuperación de errores distribuido (las retransmisiones se hacen desde ciertos encaminadores intermedios que siempre estarán más cercanos a los miembros que la propia fuente) y de ámbito restringido (el alcance de las retransmisiones está restringido a un cierto número de miembros). Este esquema hace posible optimizar el retardo medio de distribución y disminuir la sobrecarga introducida por las retransmisiones; (3) incorpora en ciertos encaminadores funciones de agregación y filtrado de paquetes de control, que evitan problemas de implosión y reducen el tráfico que fluye hacia la fuente. Con el fin de evaluar el comportamiento del protocolo diseñado, se han realizado pruebas de simulación obteniéndose como principales conclusiones que, el RMNP escala correctamente con el tamaño del grupo, hace un uso óptimo de los recursos de red y es adecuado para aplicaciones sensibles al retardo.---ABSTRACT---There are many distributed applications that require a reliable multicast service, including: distributed databases, distributed operating systems, distributed interactive simulation systems and distribution applications of software, publications or news. Although the application domain of distributed systems of this type was originally confíned to a single subnetwork (for example, a Local Área Network), it later became necessary extend their applicability to internetworks. The traditional approach to the reliable multicast problem in internetworks is based mainly on the following two points: (1) provide a lot of service guarantees in one and the same protocol (for example, reliability, atomicity and ordering) and different levéis of guarantee in some cases, without taking into account that many multicast applications that require reliability do not need other guarantees, and (2) extend solutions adopted in the unicast environment to the multicast environment without taking into account their distinctive characteristics. So, the attempted solutions to the multicast reliability problem were end-to-end protocols (transport protocols) and centralized error recovery schemata (retransmissions made from a single point, normally the source) and global error retrieval schemata (the requested packets are retransmitted to the whole group). Generally, these approaches have resulted in protocols that are inefficient in execution time, have scaling problems, do not make optimum use of network resources and are not suitable for delay-sensitive applications. Here, the multicast reliability problem is investigated in internetworks operating in datagram mode and a new way of approaching the problem is presented: it is better to solve to the multicast reliability problem at network level and sepárate reliability from other service guarantees that can be supplied by a higher protocol or the application itself. A reliable multicast protocol that operates at network level (called RMNP) has been designed on the basis of this new approach. The most representative characteristics of the RMNP are as follows: (1) it takes a transmitter-oriented approach, which provides for a very high reliability level; (2) it provides for an error retrieval schema that is distributed (the retransmissions are made from given intermedíate routers that will always be closer to the members than the source itself) and of restricted scope (the scope of the retransmissions is confined to a given number of members), and this schema makes it possible to optimize the mean distribution delay and reduce the overload caused by retransmissions; (3) some routers include control packet aggregation and filtering functions that prevent implosión problems and reduce the traffic flowing towards the source. Simulation test have been performed in order to evalúate the behaviour of the protocol designed. The main conclusions are that the RMNP scales correctly with group size, makes optimum use of network resources and is suitable for delay-sensitive applications

WWW media distribution via Hopwise reliable multicast

Repeated access to WWW pages currently makes inefficient use of available network bandwidth. A Distribution Point Model is proposed where large and relatively static sets of pages (e.g. magazines or other such media) are distributed via bulk multicast to LAN distribution points for local access. Some access control issues are discussed. Hopwise Reliable Multicast (HRM) is proposed to simplify reliable multicast of non real time bulk data between LANs. HRM uses TCP for reliability and flow control on a hop by hop basis throughout a multicast distribution tree created by today`s Internet MBone