网络工程专业英语课件ch2 Application Layer.ppt

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 2: Application Layer * P2P: centralized directory 1) when peer connects, it informs central server: IP address content 2) Alice queries for “Yesterday Once More” 3) Alice requests file from Bob centralized directory server peers Alice Bob 1 1 1 1 2 3 2: Application Layer * P2P: problems with centralized directory Single point of failure Performance bottleneck Copyright infringement 2: Application Layer * 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 2: Application Layer * Socket programming Socket API introduced in BSD4.1 UNIX, 1981 explicitly created, used, released by apps client/server paradigm two types of transport service via socket API: unreliable datagram reliable, byte stream-oriented a host-local, application-created, OS-controlled interface (a “door”) into which application process can both send and receive messages to/from another application process socket Goal: learn how to build client/server application that communicate using sockets 2: Application Layer * Socket-programming using TCP Socket: a door between application process and end-end-transport protocol (UCP or TCP) TCP service: reliable transfer of bytes from one process to another process TCP with buffers, variables socket controlled by application developer controlled by operating system host or server process TCP with buffers, variables socket controlled by application developer controlled by operating system host or server internet 2: Application Layer * Socket programming with TCP Client must contact server server process must first be running server must have created socket (door) that welcomes client’s contact Client contacts server by: creating clie