Application-level overlays Site 2 Site 3 N • One per application • Nodes are decentralized • NOC is centralized N N ISP1 ISP2 Site 1 N N ISP3 N Site 4 P2P systems are overlay networks without central control
Client-Server Versus Peer-to-Peer Network Architecture • A simple distinction • Client-server • Computers perform asymmetric functions • Peers-to-Peer (P2P) • Computers perform symmetric functions • Different architectures offer different benefits • Pure P2P networks are rare • Most P2P networks rely on centralized server for some functions
…a technology that enables two or more peers to collaborate spontaneously in a network of equal peers by using appropriate information and communication systems without the necessity for central coordination. File/information/resource sharing Equal peers Decentralization What is P2P?
Client/Server Model Peer to Peer Model Assumption Assumption Workstation is powerful enough to do some jobs Workstation is so powerlessthat it can not do any task. Other workstation and server can remote-control the workstation Only User (Operator) can control the workstation Server Server result Order result Order Pure P2P Workstation (Client) Workstation (Client) Workstation (Client)
Client-Server vs. Peer-to-Peer Example Peer-to-Peer Client–Server
Large-Scale Data Sharing:P2P Internet Client Client Cache Proxy Client Client Client server server Client Peer-to-peer model Client Client/Server Client/Server Congestion zone Client/Server Client Client Client Client/Server Client/Server server server Client/server model Client/Server Congestion zone Client/Server Client/Server Client/Server
Client-Server File SharingThe MP3.com Architecture 1. Have any Metallica songs? Machine A 2. Yes 3. Please send one 4. Here it is MP3.com Note: A few years ago, a band called Metallica sued a file sharing service (Napster) for allowing illegal music exchange over it’s network.
Peer-to-Peer File SharingIn Action • Interacting Messages • Ping: “Are you there?”: Directed at a Peer • Pong: “Yes, I am here” • Query: “I am looking for 007 posters” • Query Response: “I have the poster. Download from xxx.xxx.xxx.xxx:xx • All these messages are forwarded from a Peer to its neighbors
DFS Variations • DFS: Distributed File Sharing
Peer-to-Peer File Sharing model • Users register files with network neighbors • Search across the network to find files to copy • Does not require a centralized broker • Example:Gnutella Copying Final Fantasy 4 Bob Carol Where is Final Fantasy 4? Carol has Final Fantasy 4 Where is Final Fantasy 4? Alice Ted Carol has it
Netflow Statistics Students’ usage One hour Incoming Usage by Protocol