Normal prepaid IN call flow in GSM

Hi All,

      Prepaid Call Flow

The above flow describes a basic direct dial call scenario with normal call termination:

1. Mobile A starts a new call by dialing Mobile B. 

2. The MSC sends an IDP (Initial Detection Point) event, which notifies the IN-SCP of the new call.

  IDP Message Contains :- A-Party no, B-Party no., Service key=90, A Party Location, Time stamp.

3. The IN SCP processes the request and after authorizing the user, the IN SCP sends 3 IN messages to the MSC - 

• AC (Apply Charging) :-  Check the A-Party Balance / tariff related facilities & provides maximum granted time for a call.
• CIQ (Call Information Query) :- IN request from the MSC for call information, like CAET - Call Attempt Elapsed Time (time between call ringing & user picks the call), CCET - Call Connect Elapsed Time (Duration of a call), CST - Call Stop Time (exact time when call disconnect), RC - Release Cause (Exact release cause due to which call got disconnected).
• RRBCSM (Request Report Basic Call State Module) :- IN again request from MSC for detailed Release Cause.

4. Connect :- After getting everything OK i.e. all request from IN side have been done then IN sends a Connect message to MSC for further call processing & connect the call.

5. Activity Test :- After IN provides "connect" message to MSC, its a sort of ping message which is unidirectional, sent by IN to MSC, to know the progress of a call.

6. Once the connection is made, an event report (for answer event) is sent to SDP via IN-SCP.for preventing any revenue loss.

7. After conversation, when call gets disconnected, a new event report is sent to SDP via IN-SCP, which in turn instructs to release the call.

8. Once the call is released, a new Apply Charging Report (ACR) is sent to IN-SCP, which contains full time usage data of a call. This report is sent to SDP for accurate & final call charging.

9. CIR (Call Information Report) :- By using the details which was noted in CIQ message, MSC makes a report i.e. CIR (which contains CAET, CCET, CST, RC) & sends to SDP via IN-SCP.

10. ERB (Evert Report BCSM) :- Another report send by MSC to IN, which contains actual release cause in details, which may be - Abandon, B-Party Busy, B-Party no answer, B-Party not reachable, route selection failure, disconnect.

11. Finally signaling terminates, which ends the call.