The NPI interface consists of service primitives defined as message streams that access network services and are transferred between network user instances and network providers. There are two types of service primitives: one is generated by the network user, and the other is generated by the network operator. The service primitives of the users are Request( REQ) and Response( RSP), while those of the providers are Indication( IND) and Confirmation( CONF). Users make a request via Request or respond to an event via Response to the Provider. The primitives of the network provider consist of indication or confirmation.