When an incoming SS7 message is received (see the following figure), the SCCP compares the PC and the SSN from the message signal unit (MSU) with the internal routing tables and routes the message to the SG if the SG has registered for that PC and SSN combination. The SG routes the incoming message to the AS as follows:
Gateway Redirection can also route the incoming message to the AS based on the registered Application ID.
The SG application has reserved Application IDs. For more information, refer to Reserved Application IDs for SS7 Applications.
The following figure shows the SUA message handling from the IP to SS7 network.
The following figure shows the SUA message handling from SS7 to the IP network.