Which layer in TCP/IP assigns port numbers?

The Transport Layer is responsible for assigning port numbers in the TCP/IP model. Port numbers are essential in network communications because they enable multiple applications to communicate over the same IP address without interference. Each service or application on a device can be assigned a different port number, allowing them to send and receive data simultaneously.

In this layer, protocols such as Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) utilize these port numbers to differentiate between different data streams or connections. For example, web traffic typically uses port 80 for HTTP and port 443 for HTTPS, allowing the same device to handle web browsing alongside other services without conflict.

Other layers in the TCP/IP model, such as the Network Access Layer, Internet Layer, and Application Layer, do not engage in the assignment of port numbers. The Network Access Layer deals primarily with physical network connections and data link protocols, the Internet Layer focuses on the logical routing of packets, and the Application Layer interacts with user applications directly but relies on the Transport Layer to manage the specifics of port communication. Thus, the Transport Layer is uniquely positioned to handle the assignment and management of port numbers.