Port strategy

Only the client API can check for a new available port because a tier program can reserve a port.

Solution:

• 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).

Use case:

1. The client requests a port.
2. The client tries to open the port. If successful, the procedure is finished.
3. If not successful, the client informs the server that the port is unavailable. Go to 1.