If:
A user makes an MLPP call to another user whose telephone resides on a different MLPP server, and
The call arrives at the server of the called user over a non-ISDN-PRI trunk, and
The called telephone is busy with an existing call,
The destination server uses the following process to determine whether to grant precedence to the new call:
The server assigns the existing call to the service domain that is defined either in the COR of the caller, or by its own system service domain.
The server checks its own system service domain to define the service domain of the new call.
The server matches the service domain of the new call with the service domain of the existing call.
If the service domains match, the server matches the precedence level of the existing call with the precedence level of the new call. If the new call has a higher level, the new call preempts the existing call.
If the service domains do not match, then the server gives the new call an announcement that says that the MLPP call cannot be completed. The figure shows this process.
