大多数程序员所接触到的套接字（Socket）为两类： （1）流式套接字（SOCK_STREAM）：一种面向连接的Socket，针对于面向连接的TCP服务应用； （2）数据报式套接字（SOCK_DGRAM）：一种无连接的Socket，对应于无连接的UDP服务应用。 从用户的角度来看，SOCK_STREAM、SOCK_DGRAM这两类套接字似乎的确涵盖了TCP/IP应用的全部，因为基于TCP/IP的应用，从 协议栈的层次上讲，在传输层的确只可能建立于TCP或UDP协议之上（图1），而SOCK_STREAM、SOCK_DGRAM又分别对应于TCP和 UDP，所以几乎所有的应用都可以用这两类套接字实现。-Most programmers have access to a socket (Socket) into two categories: (1) stream socket (SOCK_STREAM): a connection-oriented Socket, for applications in service-oriented TCP connections　(2) Data News sockets (SOCK_DGRAM): a connectionless socket, corresponding to the UDP connectionless service applications. From the user s perspective, SOCK_STREAM, SOCK_DGRAM socket these two seem really covers all the TCP/IP applications, because TCP/IP-based application-level protocol stack　speaking at the transport layer is indeed possible to build only on top of TCP or UDP protocol (Figure 1), and SOCK_STREAM, SOCK_DGRAM also correspond to the TCP and UDP, so almost all of the applications can be used to achieve these two sockets.