Transport protocols run over the best-effort IP layer to provide a mechanism for applications to communicate with each other without directly interacting with the IP layer.
It’s important to note that the use of ports is crucial in the transport layer. Certainly, there can be multiple types of processes that may run on a single host at a particular time. In general, a single IP address is assigned to a host. A sender host sends the data to the receiver host with a port number. Furthermore, the receiver host can identify the port and will route the data to a specific process.