The INAP protocol stands for Intelligent Network Application Protocol. It is a protocol that enables the communication and interaction between different nodes in an intelligent network, such as the Service Switching Point (SSP), the Service Control Point (SCP), and the Specialized Resource Point (SRP). The INAP protocol is based on the SS7 protocol family and uses the services of the TCAP layer.
One of the applications of the INAP protocol is to support online charging for mobile services, such as prepaid voice calls, SMS, and data. In this case, the charging node is the SCP that holds the service logic and the charging information for the subscribers. The MSC is the SSP that handles the call routing and signaling for the mobile users. The INAP protocol allows the MSC to send triggers to the SCP based on certain events or criteria, such as the start, end, or duration of a call. The SCP then responds to the MSC with instructions on how to control the call, such as allowing, rejecting, or redirecting the call. The SCP also updates the charging records and balances for the subscribers based on the usage and consumption of the services.
The INAP protocol defines various messages and parameters for the communication between the charging node and the MSC. Some of the common messages are:
• InitialDP: This message is sent by the MSC to the SCP when a call is initiated. It contains information such as the calling and called party numbers, the service key, and the event type.
• Connect: This message is sent by the SCP to the MSC when the call is authorized and the SCP wants to connect the call to a destination. It contains information such as the destination number, the routing number, and the charging information.
• Continue: This message is sent by the SCP to the MSC when the call is authorized and the SCP wants the MSC to continue the call processing as normal. It does not contain any additional information.
• ReleaseCall: This message is sent by the SCP to the MSC when the call is not authorized or the SCP wants to terminate the call. It contains information such as the release cause and the charging information.
• ApplyCharging: This message is sent by the SCP to the MSC when the SCP wants to apply charging for the call. It contains information such as the charging type, the charging rate, and the charging duration.
• ApplyChargingReport: This message is sent by the MSC to the SCP when the MSC has applied charging for the call. It contains information such as the call duration, the call status, and the charging result.
• EventReportBCSM: This message is sent by the MSC to the SCP when a certain event occurs during the call, such as the answer, disconnect, or busy. It contains information such as the event type, the event time, and the charging information.
These are some of the main messages and functions of the INAP protocol used in intelligent networks to communicate between the charging node and the MSC. The INAP protocol enables the implementation of various value-added services and features for the mobile users, such as prepaid, call forwarding, call waiting, and call barring. The INAP protocol also ensures the accuracy and reliability of the charging and billing processes for the mobile services.
