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。

套接字基本上是网络通信的端点，至少由一个ip地址和一个端口组成。在Java/ c#中，套接字是双向连接一侧的高级实现。

还有Java教程中的一个(非规范的)定义。

首先，我认为我们应该先了解一下什么构成了从a到B的数据包。

网络的一个常见定义是使用OSI模型，该模型根据目的将网络分离为许多层。有几个重要的，我们将在这里介绍:

The data link layer. This layer is responsible for getting packets of data from one network device to another and is just above the layer that actually does the transmitting. It talks about MAC addresses and knows how to find hosts based on their MAC (hardware) address, but nothing more. The network layer is the layer that allows you to transport data across machines and over physical boundaries, such as physical devices. The network layer must essentially support an additional address based mechanism which relates somehow to the physical address; enter the Internet Protocol (IPv4). An IP address can get your packet from A to B over the internet, but knows nothing about how to traverse individual hops. This is handled by the layer above in accordance with routing information. The transport layer. This layer is responsible for defining the way information gets from A to B and any restrictions, checks or errors on that behaviour. For example, TCP adds additional information to a packet such that it is possible to deduce if packets have been lost.

TCP包含了端口的概念。这些实际上是Internet套接字(AF_INET)可以绑定到的同一IP地址上的不同数据端点。

UDP和其他传输层协议也是如此。从技术上讲，它们不需要以端口为特色，但这些端口确实为上层的多个应用程序提供了一种使用同一台计算机接收(实际上是发出)传出连接的方法。

这就把我们带到了TCP或UDP连接的解剖。每个都有一个源端口和地址，以及一个目标端口和地址。这样，在任何给定的会话中，目标应用程序都可以从源进行响应和接收。

因此，端口本质上是一种规范强制的方式，允许多个并发连接共享相同的地址。

现在，我们需要看看如何从应用程序的角度与外部世界通信。要做到这一点，你需要询问你的操作系统，因为大多数操作系统都支持伯克利套接字的方式来做事情，我们看到我们可以从应用程序创建包含端口的套接字，像这样:

int fd = socket(AF_INET, SOCK_STREAM, 0); // tcp socket
int fd = socket(AF_INET, SOCK_DGRAM, 0); // udp socket
// later we bind...

太棒了!因此，在sockaddr结构中，我们将指定端口，bam!完成工作!嗯，差不多了，除了:

int fd = socket(AF_UNIX, SOCK_STREAM, 0);

也是可能的。啊，这可真是个麻烦!

好吧，实际上并没有。我们所需要做的就是想出一些合适的定义:

internet套接字是IP地址、协议及其相关端口号的组合，服务可以在其上提供数据。tcp端口80,stackoverflow.com是一个互联网套接字。 unix套接字是一个在文件系统中表示的IPC端点，例如/var/run/database.sock。 套接字API是一种请求应用程序能够向套接字读写数据的方法。

瞧!这样就把事情整理好了。在我们的方案中，

端口是一个数字标识符，作为传输层协议的一部分，标识应该响应给定请求的服务号。

因此，端口实际上是形成互联网套接字所需的一个子集。不幸的是，“套接字”这个词的意思恰好被应用到几个不同的概念中。所以我衷心建议你为你的下一个项目命名套接字，只是为了增加混乱;)

An application consists of pair of processes which communicate over the network (client-server pair). These processes send and receive messages, into and from the network through a software interface called socket. Considering the analogy presented in the book "Computer Networking: Top Down Approach". There is a house that wants to communicate with other house. Here, house is analogous to a process, and door to a socket. Sending process assumes that there is a infrastructure on the other side of the door that will transport the data to the destination. Once the message is arrived on the other side, it passes through receiver's door (socket) into the house (process). This illustration from the same book can help you: Sockets are part of transport layer, which provides logical communication to applications. This means that from application's point of view both hosts are directly connected to each other, even though there are numerous routers and/or switches between them. Thus a socket is not a connection itself, it's the end point of the connection. Transport layer protocols are implemented only on hosts, and not on intermediate routers. Ports provide means of internal addressing to a machine. The primary purpose it to allow multiple processes to send and receive data over the network without interfering with other processes (their data). All sockets are provided with a port number. When a segment arrives to a host, the transport layer examines the destination port number of the segment. It then forwards the segment to the corresponding socket. This job of delivering the data in a transport layer segment to the correct socket is called de-multiplexing. The segment's data is then forwarded to the process attached to the socket.

端口和插座可以比作银行分行。

“银行”的门牌号与IP地址类似。 银行有不同的部分，比如:

储蓄帐务部 个人贷款部 房屋贷款部 投诉部门

因此，1(储蓄账户部)、2(个人贷款部)、3(住房贷款部)和4(申诉部)是端口。

现在让我们假设你要开一个储蓄账户，你去了银行(IP地址)，然后你去了“储蓄账户部门”(端口号1)，然后你遇到了在“储蓄账户部门”工作的一名员工。让我们称他为SAVINGACCOUNT_EMPLOYEE1，用于开户。

SAVINGACCOUNT_EMPLOYEE1是套接字描述符，因此可能存在 SAVINGACCOUNT_EMPLOYEE1到SAVINGACCOUNT_EMPLOYEEN。这些都是套接字描述符。

同样地，其他部门将有员工在他们之下工作，他们类似于插座。

这个问题已经有了理论上的答案。我想举一个实际的例子来解释这个问题，让大家对Socket和Port有一个更清晰的理解。

我在这里找到的

This example will walk you thru the process of connecting to a website, such as Wiley. You would open your web browser (like Mozilla Firefox) and type www.wiley.com into the address bar. Your web browser uses a Domain Name System (DNS) server to look up the name www.wiley.com to identify its IP address is. For this example, the address is 192.0.2.100. Firefox makes a connection to the 192.0.2.100 address and to the port where the application layer web server is operating. Firefox knows what port to expect because it is a well-known port . The well-known port for a web server is TCP port 80. The destination socket that Firefox attempts to connect is written as socket:port, or in this example, 192.0.2.100:80. This is the server side of the connect, but the server needs to know where to send the web page you want to view in Mozilla Firefox, so you have a socket for the client side of the connection also. The client side connection is made up of your IP address, such as 192.168.1.25, and a randomly chosen dynamic port number. The socket associated with Firefox looks like 192.168.1.25:49175. Because web servers operate on TCP port 80, both of these sockets are TCP sockets, whereas if you were connecting to a server operating on a UDP port, both the server and client sockets would be UDP sockets.