Which layer of the OSI model is associated with port numbers?

The layer of the OSI model associated with port numbers is Layer 4, which is known as the Transport Layer. This layer is responsible for providing end-to-end communication services for applications. One of its key functionalities is the use of port numbers to direct data packets to the appropriate application process running on a device.

Port numbers serve as communication endpoints and help differentiate multiple applications or services running simultaneously on a device. For instance, when a web browser requests a webpage, it typically uses port 80 for HTTP and port 443 for HTTPS; these port numbers inform the Transport Layer about which service to direct the traffic to once it reaches its destination.

In contrast, Layer 2, known as the Data Link Layer, deals with node-to-node data transfer and does not involve port numbers. Layer 3, or the Network Layer, is primarily concerned with routing packets across different networks but focuses on IP addresses instead of port numbers. Layer 5, the Session Layer, manages sessions between applications but does not specifically utilize port numbers in its operations. Therefore, Layer 4 is the specific layer that uses port numbers to facilitate inter-process communication within the TCP/IP protocol suite.