What is the purpose of port numbers in network communication?

Port numbers play a critical role in network communication by identifying specific protocols and services on a device. Each application that utilizes the network has a unique port number assigned to it, allowing the underlying TCP/IP protocol to determine which application should handle incoming data. For example, HTTP typically uses port 80, while FTP uses port 21. This identification is essential for the correct routing of data packets to the appropriate application layer.

While port numbers are involved in establishing connections between devices, the primary function is to distinguish between various services and applications. Segmenting data and determining packet size relate more to how data is transmitted across the network rather than how specific applications are recognized by the operating system or networking stack.