Only the client API can check for a new available port because a tier program can reserve a port.
- Add the server request PORT_UNAVAILABLE: the server stores the list of unavailable ports.
- The request REQUEST_PORT returns a port available (not in the list of unavailable ports).
- The client requests a port.
- The client tries to open the port. If successful, the procedure is finished.
- If not successful, the client informs the server that the port is unavailable. Go to 1.