I think we could include these rules into the model document, and echoed
to the protocol document, if need be, for emphasis. The following steps
would be taken, in order, to determine what port number should be used
to contact an IPP server
1. If the protocol scheme for the URI allows the port number to
be explicity included in the URI string, and an explicit port number
is specified, then that port number MUST
be used by the client to contact the IPP server.
2. If the protocol scheme for the URI does not allow an
explicit port number specification, then the default port
number for the protocol should be used.
3. Consult the appropriate IPP protocol mapping document to
determine alternamte port numbers for the protocol specified
in the server URI.