Facility IE
Supplemental services are invoked by sending facility IEs in a facility message to an ISDN
switching device such as a PBX.
Supplemental services are widely used by PBXs and in the PSTN. IP telephony systems
that are connected to these types of switches must be able to send and receive these
messages. The supplemental service and associated parameters that are invoked are PBXspecific
and should be provided by the PBX manufacturer.