Centralized: pros and cons Decentralized Every user acts as a client, a server or oth (servent). More effective, comprehensive searches User connects to framework and becomes a s Access is controlled member of the community, allowing others to connect through him/her u cons Users speak directly to other users with no System has single points of entry: one intermediate or central authority fails could bring whole system down Not one entity controls the information Broken links, out of date information. that passes through the community GNUTELLA GNUTELLA Gnutella works more or less like a pure P2P model Key terms: gnutella is downloaded and installed on the Servent: client+server sage is sent to a computer, which passes Firewall: a shield that protects inside the gnutella to the Broadcasting: messaging service between servents in Gnutella is a client-based software that has a file Gnutella sharing service and a mini search engine A machine which installed Gnutel serve the dropped et wk en ges of data that have been lost of content by sending requests Searching on Gnutella is almost like working with request to the servent for uploading the file. This is Gnutella facilitates to share all kinds of fil Port: default port number for Gnutella servents is 6346 Example: GNUTELLA Example: GNUTELLA 习ac4 哈工大计算机学院 李全龙 Network Application Development P2P Application Development 19 Centralized: pros and cons „ pros „ More effective, comprehensive searches „ Access is controlled „ cons „ System has single points of entry; one fails could bring whole system down „ Broken links, out of date information. 哈工大计算机学院 李全龙 Network Application Development P2P Application Development 20 Decentralized „ Every user acts as a client, a server or both (servent). „ User connects to framework and becomes a member of the community, allowing others to connect through him/her „ Users speak directly to other users with no intermediate or central authority „ Not one entity controls the information that passes through the community 哈工大计算机学院 李全龙 Network Application Development P2P Application Development 21 GNUTELLA „ Gnutella works more or less like a pure P2P model „ Gnutella is downloaded and installed on the computer „ A message is sent to a computer, which passes it to the other computers „ Gnutella is a client-based software that has a file￾sharing service and a mini search engine „ A machine which installed Gnutella can serve the requests of other users, and can find the desired content by sending requests „ Searching on Gnutella is almost like working with any other search engine „ Gnutella facilitates to share all kinds of files 哈工大计算机学院 李全龙 Network Application Development P2P Application Development 22 GNUTELLA „ Key terms: „ Servent: client+server „ Horizon: a group of servents, not entire Gnutella „ Firewall: a shield that protects users inside the Gnutella „ Broadcasting: messaging service between servents in Gnutella „ Dropped Packets: packages of data that have been lost of dropped across the Gnutella nerwork „ Push Request: whenever a client behind the firewall is unable to download a file from a servent, the firewall send a request to the servent for uploading the file. This is called a push request. „ Port: default port number for Gnutella servents is 6346 哈工大计算机学院 李全龙 Network Application Development P2P Application Development 23 Example: GNUTELLA 哈工大计算机学院 李全龙 Network Application Development P2P Application Development 24 Example: GNUTELLA