When we making call, It reaches MSC, Then MSC sends IAM (Initial Address Message) to SWITCH.
Switch sends IDP to SCP. This IDP contains A party number, B party number, Serving Location Details.
SCP will check A party number, B party number, Serving Location Details and sends initial request to RRBS.
Then RRBS will check balance. if A number having sufficient balance , Then RRBS sends initial response to SCP.
SCP sends Apply charging request (ACReq) to MSC. ACReq contains First granted time in seconds.
Then SCP sends RRBCSM, CIReq, and CONNECT to MSC. Here RRBCSM – Request Report Basic Call State Model contains Detection points DP-(4,5,6,7,9,10). CIReq contains Call elapsed time, call start time and Release cause which are requested from SCP to MSC.
Switch sends the Address complete message to MSC. Then MSC sends Answer Message to switch.
Switch sends the Event Report BCSM DP7 – (O_Answer) to SCP. Now call is connected, (A party, B parties are connected in call).
When anyone party disconnected means, Release is sends from MSC to SWITCH. SWITCH sends ACRep to SCP as Call Active : FALSE. SCP sends terminate request to RRBS.
Also SWITCH sends ERBCSM as DP9 – O_Disconnect to SCP.
Finally RRBS sends Terminate response to SCP. SCP sends release to SWITCH. SWITCH sends release to MSC.