计网第二章.ppt

Chapter 2: Application layer 2.1 Principles of network applications 2.2 Web and HTTP 2.3 FTP 2.4 Electronic Mail SMTP, POP3, IMAP 2.5 DNS 2.6 P2P Applications 2.7 Socket programming with TCP 2.8 Socket programming with UDP Chapter 2: Application layer 2.1 Principles of network applications 2.2 Web and HTTP 2.3 FTP 2.4 Electronic Mail SMTP, POP3, IMAP 2.5 DNS 2.6 P2P file sharing 2.7 Socket programming with TCP 2.8 Socket programming with UDP 2.9 Building a Web server Network Application architectures How to structure application over various end systems (vs. network architecture) Client-server Peer-to-peer (P2P) Hybrid of client-server and P2P 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 Pure P2P architecture Hybrid of client-server and P2P Instant messaging chatting between two users is P2P centralized service: client presence detection/location user registers its IP address with central server when it comes online user contacts central server to find IP addresses of buddies Skype voice-over-IP P2P application centralized server: finding address of remote party: client-client connection: direct (not through server) Processes communicating Process: program running within a host. within same host, two processes communicate using inter-process communication (defined by OS). processes in different hosts communicate by exchanging messages Net. App.: pairs of processesж, eg. Web, P2P Client process: process that initiates communication Server process: process that waits to be contacted Sockets: process/network interface process sends/receives messages to/from its socket (soft. interface) socket analogous to door sending process shoves message out door sending process relies on transport infrastructure on other side of door which brings message to socket at receiving process