Pure P2P Model P2P with Simple Discovery Server Such P2P models do not actually n computers (clients Peers find other connected eers to the incoming ut ary assistance from a ommunication still remains the job of Pure P2P models provide almost ne chances of working with the Interne a peer has to Pzp problem with the pure cted peer individually May need more tim P2P with a Discovery and Lookup P2P with a Discovery, Lookup Server and Content Server The server dominates as in a list of connected peers along with typical client/server architecture Peers are not permitted to 旦 This model reduces the burden on connect with each other directly The server initiates communication between two peers hat the server slows down if eers establish communication too many requests come up and perform various activities multaneously There is single point of failure in server Existing P2P Applications Centralized Napster a Napste Napster used centralized servers to keep a Gnutella atalog of available files, ( 3rd model) serve The central server3 哈工大计算机学院 李全龙 Network Application Development P2P Application Development 13 Pure P2P Model „ Pure P2P model entirely depends on computers (clients in the C/S model) „ Peers find other connected peers on the network dynamiclly „ The entire communication occurs among connected peers without any assistance from a server „ Pure P2P models provide almost plug-and-play features for working with the Internet „ The only problem with the pure P2P model is finding peers 哈工大计算机学院 李全龙 Network Application Development P2P Application Development 14 P2P with Simple Discovery Server „ Such P2P models do not actually involve a server „ The role of the server is restricted to providing the names of already connected peers to the incoming peer „ The server only assists peers by providing a list of connected peers „ Establishing connection and communication still remains the job of the peers „ This model increases the chances of finding a larger number of peers „ To download a resource, a peer has to approach each connected peer individually „ May need more time 哈工大计算机学院 李全龙 Network Application Development P2P Application Development 15 P2P with a Discovery and Lookup Server „ The server is used to provide the list of connected peers along with the resources available „ This model reduces the burden on peers „ The server initiates communication between two peers „ Once again, the two connected peers establish communication, and perform various activities 哈工大计算机学院 李全龙 Network Application Development P2P Application Development 16 P2P with a Discovery, Lookup, and Content Server „ The server dominates as in a typical client/server architecture „ Peers are not permitted to connect with each other directly „ All resources are stored in the database of the server „ Major disadvantage of this model is that the server slows down if too many requests come up simultaneously „ There is single point of failure in server 哈工大计算机学院 李全龙 Network Application Development P2P Application Development 17 Existing P2P Applications „ Napster „ Gnutella 哈工大计算机学院 李全龙 Network Application Development P2P Application Development 18 Centralized: Napster „ Napster used centralized servers to keep a catalog of available files. (3rd model) 1. User sends out request Napster searches central database Search request 2. The central server sends back a list of available files for download Search response Napster server user user user user 3. Requesting user downloads the file directly from another Napster user computer Download from user