What is the usual procedure taken if an unrecognized non-mandatory ISDN IE is received by a network?

What is the usual procedure taken if an unrecognized non-mandatory ISDN IE is received by a network?

A.
Final handle the call

B.
Final handle the call if 2 such IE is received

C.
Ignore only if the IE received is not CS0, otherwise final handle the call

D.
Send a Facility msg to the user notifying the user of sending unknown IEs but don’t final handle

E.
Ignore the IEs