TCP (Transmission Control Protocol) is a commonly used network transmission protocol that identifies different network applications or services by using port numbers. The port number is a 16-bit integer, ranging from 0 to 65535. The port numbers between 0 and 1023 are called "well-known ports" and are used for some common services, such as HTTP (port number 80), FTP (port number for 21) etc. In programming, we can use port numbers to identify and distinguish different network applications for communication and data exchange.
The purpose of the port number is to distinguish their communications through different port numbers when multiple network applications are running simultaneously on a host. Each TCP connection requires a local port and a remote port to uniquely identify it. The local port is the port on the host used to send and receive data, while the remote port is the port on the remote host. A TCP connection can be uniquely determined by the combination of source IP address, source port, destination IP address, and destination port.
In programming, different programming languages provide different ways to use port numbers. The following uses the Python language as an example to demonstrate how to use TCP port numbers for network communication in programming.
import socket
# 创建一个TCP/IP套接字
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM