Publication: Diseño y evaluación de la interconexión de redes peer-to-peer estructuradas usando una topología jerárquica
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2010-03
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2010-03-25
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Abstract
El tráfico en Internet está evolucionando continuamente. En el siglo XX, la mayor parte del tráfico en Internet soportado por los Proveedores de Servicios de Internet (ISP’s en terminología anglosajona) estaba relacionado con el tráfico web. Sin embargo, actualmente, el tráfico en Internet ha evolucionado drásticamente. La mayor parte del tráfico en Internet es tráfico Peer-to-Peer. Este cambio cambia completamente la situación en comparación con el siglo anterior, de ahí la relevancia del paradigma de las redes Peer-to-Peer. La adopción de las redes Peer-to-Peer está principalmente motivada por su uso en aplicaciones de compartición de ficheros pero la aplicación de las redes Peer-to-Peer no está sólo limitada al paradigma de compartición de ficheros. De hecho, las redes Peer-to-Peer son adecuadas para el desarrollo de cualquier servicio o aplicación distribuida ya que permiten almacenar información de manera distribuida entre un conjunto de nodos. Además, también permiten recuperar esa información cuando sea necesario. Una aplicación relevante basada en redes Peer-to-Peer es Skype la cual permite un servicio de VoIP entre varios millones de personas. Sin embargo, la interoperabilidad entre diferentes redes Peer-to-Peer no ha sido resuelta todavía. Cada red Peer-to-Peer define su propio mecanismo y su propio formato de paquete. Por lo tanto, sería deseable definir algún mecanismo que permita el intercambio de información entre diferentes redes Peer-to-Peer. Esta Tesis define un mecanismo que permite el intercambio de información entre diferentes redes Peer-to-Peer estructuradas, concretamente redes overlay basadas en DHT’s (Distributed Hash Tables). Este mecanismo está basado en un formato común de paquete, que asegura la interoperabilidad entre diferentes redes overlay, y en una arquitectura jerárquica. Esta arquitectura jerárquica está compuesta por dos niveles de jerarquáa. El nivel más bajo de la jerarquía está compuesto por las diferentes redes overlay que desean estar interconectadas. Cada una de estas redes overlay puede usar cualquier DHT, no existe ninguna restricción al respecto. Al menos un super-peer existe en cada una de estas redes overlay del nivel inferior; además, estos super-peer también participan en el nivel superior. Al nivel superior se le conoce como Red de Interconexión y está compuesto sólo por una red overlay. Su función es similar al servicio de DNS pero en el área de las redes Peer-to-Peer. En la Red de Interconexión se guarda la información de localización de cada uno de los super-peers y también el dominio o la overlay a la que representan. Por lo tanto, si un recurso de otra red quiere ser recuperado, un peer tiene que reenviar la petición a su super-peer. El super-peer consulta a la Red de Interconexión para localizar al super-peer que se hace cargo de la red destino donde se encuentra el recurso deseado y una vez que se localizar al super-peer, se le reenvía la petición. Finalmente, el super-peer en la red destino buscar el recurso deseado y lo envía de vuelta al peer que originó la petición. La arquitectura propuesta ha sido estudiada analíticamente para asegurar que el rendimiento es razonable en comparación con otras redes Peer-to-Peer. Además, la propuesta es validada con una herramienta de simulación para asegurar que las asunciones en el modelo analítico no afectan en un escenario más general. Finalmente, una implementación real sobre un entorno controlado es mostrada para demostrar la aplicabilidad y viabilidad de la propuesta. Los escenarios para las simulaciones y la verificación de la implementación han sido diseñados con especial cuidado para tener unas condiciones lo más cercanas posibles a escenarios reales.---------------------------------------------------------------------------------------------------------------------
The traffic in the Internet is evolving continuously. In the 20th century, the most traffic supported by Internet Service Providers (ISP’s) was related with web traffic. However, nowadays, the traffic in the Internet has evolved drastically; now, most of the traffic in the Internet is Peer-to-Peer traffic. This fact changes completely the situation in comparison with the end of the previous century, thus the relevance of the Peer-to-Peer paradigm nowadays is evident. The adoption of Peer-to-Peer overlay networks was firstly motivated for its usage in file-sharing applications but the applicability of Peer-to-Peer overlay networks is not only limited to this kind of applications. In fact, Peer-to-Peer overlay networks are suitable for the development of any distributed application or service since they allow the allocation and retrieval of information in a distributed fashion among a set of nodes. However, each overlay network has its own structure and mechanisms to distribute the information among all nodes. Additionally, each Peer-to-Peer overlay network implementation usually defines its own packet format. Therefore, the interoperability among different overlay networks is not possible. This Thesis defines a mechanism to allow the exchange of information among different structured Peer-to Peer overlay networks, concretely DHT (Distributed Hash Table) overlay networks. This mechanism is based on both a common packet format, which assures the interoperability among different overlay networks, and on a hierarchical architecture. This hierarchical architecture has two levels of hierarchy. The lower level of the hierarchy is composed by the different overlay networks that want to be interconnected. Each one of these overlay networks can use any DHT overlay network with no restrictions. In addition, each overlay network in the lower level has at least one special peer, called super-peer. These super-peers are attached to the top level. This top level is named Interconnection Overlay and it is composed by just one overlay network. The purpose of super-peers is to route the queries among different overlay networks and they use the Interconnection Overlay to achieve this objective. In this Interconnection Overlay, the location information of each one of the superpeers and the overlay network represented by them are stored. Therefore, super-peers can forward the queries with the information stored in the Interconnection Overlay. If a resource placed in other overlay network wants to be obtained, a peer has to forward the query to its super-peer. The super-peer gets from the Interconnection Overlay the information about the super-peer that takes care of the destination overlay network and forwards this request. Finally, the super-peer in the destination overlay network looks for the desired resource and once is retrieved the answer is sent back to the requester. The proposed architecture is mathematically analysed to obtain is performance in term of hops and number of overlay routing entries in peers. Furthermore, the proposal is validated with a simulation tool to assure that the assumptions in the analytical model have been enough accurate. Finally, a real implementation over a controlled environment demonstrates the applicability and viability of the proposal and allows removing many of the original assumptions. The scenarios for the simulation analysis and the evaluation of the implementation have been designed carefully in order to define conditions as similar as possible to the real world.
The traffic in the Internet is evolving continuously. In the 20th century, the most traffic supported by Internet Service Providers (ISP’s) was related with web traffic. However, nowadays, the traffic in the Internet has evolved drastically; now, most of the traffic in the Internet is Peer-to-Peer traffic. This fact changes completely the situation in comparison with the end of the previous century, thus the relevance of the Peer-to-Peer paradigm nowadays is evident. The adoption of Peer-to-Peer overlay networks was firstly motivated for its usage in file-sharing applications but the applicability of Peer-to-Peer overlay networks is not only limited to this kind of applications. In fact, Peer-to-Peer overlay networks are suitable for the development of any distributed application or service since they allow the allocation and retrieval of information in a distributed fashion among a set of nodes. However, each overlay network has its own structure and mechanisms to distribute the information among all nodes. Additionally, each Peer-to-Peer overlay network implementation usually defines its own packet format. Therefore, the interoperability among different overlay networks is not possible. This Thesis defines a mechanism to allow the exchange of information among different structured Peer-to Peer overlay networks, concretely DHT (Distributed Hash Table) overlay networks. This mechanism is based on both a common packet format, which assures the interoperability among different overlay networks, and on a hierarchical architecture. This hierarchical architecture has two levels of hierarchy. The lower level of the hierarchy is composed by the different overlay networks that want to be interconnected. Each one of these overlay networks can use any DHT overlay network with no restrictions. In addition, each overlay network in the lower level has at least one special peer, called super-peer. These super-peers are attached to the top level. This top level is named Interconnection Overlay and it is composed by just one overlay network. The purpose of super-peers is to route the queries among different overlay networks and they use the Interconnection Overlay to achieve this objective. In this Interconnection Overlay, the location information of each one of the superpeers and the overlay network represented by them are stored. Therefore, super-peers can forward the queries with the information stored in the Interconnection Overlay. If a resource placed in other overlay network wants to be obtained, a peer has to forward the query to its super-peer. The super-peer gets from the Interconnection Overlay the information about the super-peer that takes care of the destination overlay network and forwards this request. Finally, the super-peer in the destination overlay network looks for the desired resource and once is retrieved the answer is sent back to the requester. The proposed architecture is mathematically analysed to obtain is performance in term of hops and number of overlay routing entries in peers. Furthermore, the proposal is validated with a simulation tool to assure that the assumptions in the analytical model have been enough accurate. Finally, a real implementation over a controlled environment demonstrates the applicability and viability of the proposal and allows removing many of the original assumptions. The scenarios for the simulation analysis and the evaluation of the implementation have been designed carefully in order to define conditions as similar as possible to the real world.
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Keywords
Peer-to-peer, Redes overlay, Peer-to-peer jerárquico, Redes overlay jerárquicas, Interconexión de redes, P2PSIP, Overlay networks, Hierarchical Peer-to-peer, Hierarchical overlay networks, Interconnection of Peer-to-peer networks