L9-p2p.ppt - Peer-to-Peer Computing CS587x Lecture...

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Peer-to-Peer Computing CS587x Lecture Department of Computer Science Iowa State University
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What to Cover Review on some P2P applications Napster Gnutella Freenet Discussion and summary
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Resource Sharing Questions to answer in order to design a resource-sharing network How to add new nodes to the network How can one node know about others How can a node find and retrieve data How to manage the shared data users
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Client/Server Architecture Create a server to store the information that these nodes want to share The server is the only data source Clients request data from server Example: mp3.com A client registers to mp3.com and uploads its music files to the server The songs are then stored and indexed on a server that is part of the web site Other users can connect to the web site and downloads the songs they are interested in Limitation of C/S model Scalability is hard to achieve Presents a single point of failure Requires administration Unused resource at the network edge
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Some P2P Applications Napster Gnutella Freenet
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Napster Each node registers to napster.com and provides a list of its song titles The napster server knows the music titles and their sites The songs themselves are still stored locally For a node to download a song, the node contacts the server The server returns a list of nodes that have the song The requesting node selects one of the nodes in the list to download the file directly from the node
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Highlights of Napster Main innovation: a client downloads a music directly from another client, i.e., P2P communication After a client downloads a music, it can serves other clients Napster server itself does not have any music files It acts as a directory or broker Advantages Each consumer contributes its resource (disk and bandwidth) and content to the community Contents are more reliable because the same file is stored in many nodes, which are geographically distributed Administration and service cost are minimal Drawback Napster is a hybrid P2P system since a central server is required to coordinate file sharing The central server presents a single point of failure
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Gnutella Creating a Gnutella network A node joins the network with a PING to announce self IP address, port, number/size of shared files Receivers forward the Ping to their neighbors Receivers back-propagate a PONG to announce self
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