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Chapter18 - Chapter 18 Peer-to-peer Computing and Overlay...

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Chapter 18: Peer-to-peer Computing and Overlay Graphs Ajay Kshemkalyani and Mukesh Singhal Distributed Computing: Principles, Algorithms, and Systems Cambridge University Press A. Kshemkalyani and M. Singhal (Distributed Computing: Principles, Algorithms, and Systems) Peer-to-peer Computing and Overlay Graphs CUP 2008 1 / 55
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Distributed Computing: Principles, Algorithms, and Systems Characteristics P2P network: application-level organization of the network to flexibly share resources All nodes are equal; communication directly between peers (no client-server) Allow location of arbitrary objects; no DNS servers required Large combined storage, CPU power, other resources, without scalability costs Dynamic insertion and deletion of nodes, as well as of resources, at low cost Features Performance self-organizing large combined storage, CPU power, and resources distributed control fast search for machines and data objects role symmetry for nodes scalable anonymity efficient management of churn naming mechanism selection of geographically close servers security, authentication, trust redundancy in storage and paths Table: Desirable characteristics and performance features of P2P systems. A. Kshemkalyani and M. Singhal (Distributed Computing: Principles, Algorithms, and Systems) Peer-to-peer Computing and Overlay Graphs CUP 2008 2 / 55
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Distributed Computing: Principles, Algorithms, and Systems Napster Central server maintains a table with the following information of each registered client: (i) the client’s address (IP) and port, and offered bandwidth, and (ii) information about the files that the client can allow to share. A client connects to a meta-server that assigns a lightly-loaded server. The client connects to the assigned server and forwards its query and identity. The server responds to the client with information about the users connected to it and the files they are sharing. On receiving the response from the server, the client chooses one of the users from whom to download a desired file. The address to enable the P2P connection between the client and the selected user is provided by the server to the client. Users are generally anonymous to each other. The directory serves to provide the mapping from a particular host that contains the required content, to the IP address needed to download from it. A. Kshemkalyani and M. Singhal (Distributed Computing: Principles, Algorithms, and Systems) Peer-to-peer Computing and Overlay Graphs CUP 2008 3 / 55
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Distributed Computing: Principles, Algorithms, and Systems Structured and Unstructured Overlays Search for data and placement of data depends on P2P overlay (which can be thought of as being below the application level overlay) Search is data-centric, not host-centric Structured P2P overlays: I E.g., hypercube, mesh, de Bruijn graphs I rigid organizational principles for object storage and object search Unstructured P2P overlays: I Loose guidelines for object search and storage I Search mechanisms are ad-hoc, variants of flooding and random walk
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