计算机网络与因特网课件.ppt

PART IV Network Applications Chapter 27 The Socket Interface Socket 接口 27.1 Introduction The interface between an application and protocol software. How an application uses protocol software to communication. Set of procedures that an application uses to become a client or a server, to contact a remote destination, or to transfer data. 27.2 Application Program Interface Client and server application use transport protocols to communicate. The interface an application uses when it interacts with transport protocol software is known as an Application Program Interface (API). An API defines a set of operations that an application can perform when interacting with protocol software, the API determines the functionality that is available. 27.3 The Socket API Although protocol standards allow operating system designers to choose an API, many have adopted the Socket API. The Socket API is available for many operating systems. The Socket API originated as part of the BSD Unix operating system. The Socket API is a de facto standard. 27.4 Sockets And Socket Libraries In BSD Unix and the system derived from it,socket functions are part of the operating system itself. In many cases,instead of modifying their basic operating system,vendors created a socket library that provides the Socket API. A socket library can provide applications with a socket API on a computer system that does not provide native sockets. When an application calls one of the socket procedures, control passes to a library routine that makes one or more calls to the underlying operating system to implement the socket function. 27.5 Socket Communication And Unix I/O An application communicates through a socket similar to the way the application transfers data to or from a file. Unix uses an open-read-write-close paradigm for all I/o 补充： 1. Socket API与Unix Unix是一个通用的交互式多用户分时操作系统。 Unix由ATT 公司Bell实验室于1969年开发。 Unix 有两个主要的流派：System V 和 BSD System V 由最初的ATT Unix 演化而来。 BSD Unix 是由加州大学伯克利(Berkeley) 分校开发，其目标是提