似乎有很多答案将socket等同于2台PC之间的连接。我认为这是完全错误的。套接字一直是一台PC上的端点，可能连接也可能不连接-当然我们都在某些时候使用侦听器或UDP套接字*。重要的部分是它是可寻址的和活跃的。向1.1.1.1:1234发送消息不太可能起作用，因为没有为该端点定义套接字。

套接字是特定于协议的-因此，TCP/IP和UDP/IP都使用* (ipaddress:port)的唯一性实现与eg不同。， IPX (Network, Node, and…嗯哼，套接字——但是一个不同的套接字是指一般的“套接字”术语。IPX套接字号相当于IP端口)。但是，它们都提供了唯一的可寻址端点。

由于IP已成为主导协议，端口(在网络术语中)已成为UDP或TCP端口号的同义词——后者是套接字地址的一部分。

UDP is connection-less - meaning no virtual circuit between the 2 endpoints is ever created. However, we still refer to UDP sockets as the endpoint. The API functions make it clear that both are just different type of sockets - SOCK_DGRAM is UDP (just sending a message) and SOCK_STREAM is TCP (creating a virtual circuit). Technically, the IP header holds the IP Address, and the protocol on top of IP (UDP or TCP) holds the port number. This makes it possible to have other protocols (eg. ICMP that have no port numbers, but do have IP addressing information).

I know that there are lot of explanations. But, there is one more easy way to understand with practical example. We all can connect to HTTP port 80, but does it mean only one user can connect to that port at a time?. The answer is obviously 'no'. Multiple users for multiple purposes can access HTTP port 80 but they still get proper response they are waiting for, from the server, can't they?. Now think about it for a minute, how?. Yes you are correct, its IP address that uniquely identifies different users who contacts for different purposes. If you would have read the previous answers before reaching here, you would know that IP address is a part of information that socket consists. Think about it, is it possible to have a communication without sockets?. The answer is 'Yes' but you cannot run more than one application in a port but we know that we are not a 'Dump' switch that runs on just hardware.

一般来说，你会得到很多理论，但区分这两个概念的最简单方法之一是:

为了获得服务，你需要一个服务号码。这个服务号码称为端口。就这么简单。

例如，HTTP as a service运行在端口80上。

现在，许多人都可以请求该服务，并建立了来自客户机-服务器的连接。会有很多联系。每个连接代表一个客户端。为了维护每个连接，服务器为每个连接创建一个套接字来维护其客户端。

套接字= IP地址+端口(数字地址) 它们一起标识机器上网络连接的端点。(我刚刚是不是网络基础课不及格?)

A socket represents a single connection between two network applications. These two applications nominally run on different computers, but sockets can also be used for interprocess communication on a single computer. Applications can create multiple sockets for communicating with each other. Sockets are bidirectional, meaning that either side of the connection is capable of both sending and receiving data. Therefore a socket can be created theoretically at any level of the OSI model from 2 upwards. Programmers often use sockets in network programming, albeit indirectly. Programming libraries like Winsock hide many of the low-level details of socket programming. Sockets have been in widespread use since the early 1980s.

端口表示网络通信的端点或“通道”。端口号允许同一计算机上的不同应用程序在不相互干扰的情况下利用网络资源。端口号最常出现在网络编程中，尤其是套接字编程中。但是，有时端口号对普通用户是可见的。例如，一个人在因特网上访问的一些网站使用如下URL:

http://www.mairie-metz.fr:8080/在本例中，数字8080指Web浏览器连接到Web服务器所使用的端口号。通常，Web站点使用端口号80，该端口号不需要包含在URL中(尽管可以包含)。

在IP组网中，端口号理论上可以在0到65535之间。但是，大多数流行的网络应用程序使用范围较低的端口号(例如HTTP的80)。

注意:术语端口还指网络技术的其他几个方面。端口可以指外部设备的物理连接点，如串口、并口和USB端口。术语端口也指某些以太网连接点，例如集线器、交换机或路由器上的连接点。

ref http://compnetworking.about.com/od/basicnetworkingconcepts/l/bldef_port.htm

ref http://compnetworking.about.com/od/itinformationtechnology/l/bldef_socket.htm

套接字由三部分组成:

IP地址 传输协议 端口号

端口是1到65535之间的数字，表示设备中的逻辑门。 客户端和服务器之间的每个连接都需要一个惟一的套接字。

例如:

1030为端口。 (10.1.1.2, TCP，端口1030)是一个套接字。