What is the primary function of a port number in TCP/IP systems?

The primary function of a port number in TCP/IP systems is to serve as a numeric value that identifies specific applications and services. Port numbers help differentiate between various services running on a host. Each application or process on a computer communicates over the network using its own port number, allowing multiple services to operate simultaneously without interference. For example, web traffic typically uses port 80 for HTTP and port 443 for HTTPS, while other applications like FTP or SSH have their designated ports as well.

This identification process is crucial for the proper functioning of network communications, as it enables devices to send and receive data correctly aligned with the intended service. By utilizing port numbers, the underlying transport layer can direct inbound packets to the correct application, ensuring that data reaches its destination effectively.