PDF of this tutorialThe prepaid subscriber initiates a call within the home area. When the S_MSC detects the origination attempt, it sends an ORREQ to its RSU. The RSU determines that the MIN is a prepaid account and queries the market server for talk time available to this account. The market server calculates the available talk time and forwards it to the RSU.
The RSU sends an orreq to the S_MSC to indicate that call processing can continue. The S_MSC attempts to connect the call. When the S_MSC detects an answer, it sends an OANSWER to the RSU. The RSU begins timing the call, and the call is connected.
During the call, the RSU detects that the subscriber's balance has reached the low threshold. The RSU then sends a CCDIR to the S_MSC, indicating that the subscriber should hear the low-balance warning. The S_MSC plays the low-balance warning to the subscriber. The S_MSC responds to the RSU with a ccdir to indicate that the low-balance warning was played.
The subscriber ends the call. The S_MSC sends an ODISCONNECT to the RSU. The RSU stops timing the call and sends the call duration to the market server. The market server prices the call and decrements the subscriber's account. The RSU sends an odisconnect to the S_MSC and the S_MSC releases the call.
Figure 4: Mid Call Zero Talk Time
