Relationships Sockets, protocols, and ports
Sockets, protocols, and ports的关系
操作方法
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Figure 1.2 depicts the logical relationships among applications, socket abstractions, protocols, and port numbers within a single host. There are several things to note about these relationships. First, a program can have multiple sockets in use at the same time. Second, multiple programs can be using the same socket abstraction at the same time, although this is less common. The figure shows that each socket has an associated local TCP or UDP port, which is used to direct incoming packets to the application that is supposed to receive them. Earlier we said that a port identifies an application on a host. Actually, a port identifies a socket on a host. There is more to it than this, however, because as Figure 1.2 shows, more than one socket can be associated with one local port. This is most common with TCP sockets; fortunately, you need not understand the details to write client-server programs that use TCP sockets. The full story will be revealed in Chapter 7.