Application Architecture Client-server architecture Client-server a P2P nt IP address Hybrid clients: communicate with server may be intermittently addresses do not communicate directly Pure p2P architecture Hybrid of client-server and P2P Napster arbitrary end systems File transfer P2P File search centralized: peers are intermittently Peers register content at central serve Peers query same central server to locate content example: Gnutella Instant messaging Chatting between two users is P2P Presence detection/location centralized Highly scalable User registers its IP address with central server User contacts central server to find iP addresses of But difficult to manage From the Client/server Model to P2P Various P2P Models P2P-based models decrease the dependency on the P2P models can be divided into the Some P2P models do not requires servers following categories No single point of failure problems in P2P Pure P2p Both models have advantages as well as P2P with a simple discovery server Another advantage of P2P is that companies can P2P with discovery and lookup servers P2P with discovery, lookup, and content servers terms of sharing resources and costs incurred on servers2 哈工大计算机学院 李全龙 Network Application Development P2P Application Development 7 Application Architecture „ Client-server „ P2P „ Hybrid 哈工大计算机学院 李全龙 Network Application Development P2P Application Development 8 Client-server architecture server: „ always-on host „ permanent IP address „ server farms for scaling clients: „ communicate with server „ may be intermittently connected „ may have dynamic IP addresses „ do not communicate directly with each other 哈工大计算机学院 李全龙 Network Application Development P2P Application Development 9 Pure P2P architecture „ no always on server „ arbitrary end systems directly communicate „ peers are intermittently connected and change IP addresses „ example: Gnutella Highly scalable But difficult to manage 哈工大计算机学院 李全龙 Network Application Development P2P Application Development 10 Hybrid of client-server and P2P Napster „ File transfer P2P „ File search centralized: „ Peers register content at central server „ Peers query same central server to locate content Instant messaging „ Chatting between two users is P2P „ Presence detection/location centralized: „ User registers its IP address with central server when it comes online „ User contacts central server to find IP addresses of buddies 哈工大计算机学院 李全龙 Network Application Development P2P Application Development 11 From the Client/Server Model to P2P „ P2P-based models decrease the dependency on the server „ Some P2P models do not requires servers „ No single point of failure problems in P2P „ Both models have advantages as well as disadvantages „ Another advantage of P2P is that companies can build collective computing powers „ P2P has shaken the boundaries of networking in terms of sharing resources and costs incurred on servers 哈工大计算机学院 李全龙 Network Application Development P2P Application Development 12 Various P2P Models „ P2P models can be divided into the following categories: „ Pure P2P „ P2P with a simple discovery server „ P2P with discovery and lookup servers „ P2P with discovery, lookup, and content servers