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Mobile Prepaid services using Intelligent Network (IN): A quick tour

Manish Das

The two most common services which are being offered to mobile customers under the

umbrella of IN services is Prepaid and Virtual Private Network (VPN) for CorporatePlan.

The main equipment used in IN architecture of mobile services are :

Service Control Point (SCP) Service Switching Point (SSP)

SCP is the central node which controls the call setup, charging and tearing down of an IN

call. The logic and data required to execute an IN service is located in a SCP.

SSP functionality ( known as SSF) is usually integrated with the MSC. SSP interrogates

SCP for IN call handling. Based on the instruction received from SCP, SSP performs:

Call processing and switching Supervision of Call duration Feeding of announcement

For Calling Party Pay (CPP) system as in India SCP interrogation is not done for

incoming calls of Prepaid numbers when they are in home network (HPLMN). This is

done because incoming calls are free and it saves resources of SSP and SCP.

In a system with large number of customer base, it is more efficient to store the data

related to a service in a dedicated database. This node is called the Service Data Point

(SDP). Depending on the amount of data to be handled, this database may be a stand-alone or it may be integrated within the SCP node. SDP performs

maintaining account data all charging administration rating of calls post processing of CDR .

Rating includes charging analysis and reservation of money on the account. The SDP alsoprovides the SCP with relevant data required for call control.

IVRS provides the necessary announcements.

Another node known as Prepaid Administration System (PPAS) performs all subscriber

and voucher administrative functions, such as:

voucher maintenance refill and balance inquiries subscriber provisioning administration of account lifecycle with expiry dates (Validity, Grace and

additional grace period etc.) and issues instruction to HLR for service deactivation

or call barring and to SDP to clear the balance.

bars IVR access for a subscriber after multiple (3 times, customizable by serviceprovider) recharge attempts with wrong activation number

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SCP, PPAS and SDP are central nodes and can serve multiple license area depending

on traffic load, connectivity and other physical issues.

Recharging of account:

1. The recharge call is initiated by the subscriber by dialing 123.

2. The call is routed to the IVR, which is in our case collocated with MSC, where the

subscriber receives a voice prompt, with instruction the subscriber what to do.

3. When the subscriber enters the activation code number, this information together withthe MSISDN of the subscriber is sent to PPAS for verification. If all information is

correct the request for recharge will be accepted and processed.4. The IVR will use the voice prompt to notify the subscriber of the result.

5. The call is ended.

7. The account is increased in the SDP database.

IN call flow for Mobile originating call from a Prepaid number:

1. The call is initiated by a Prepaid subscriber. MSC/VLR identify that the call requires

an IN service and contacts the SSP which is within MSC itself.

2 The SSF determines which SCP must be contacted for the service and identifies the

call data, which must be sent to that SCP. The SSP requests instructions from the SCPabout how to implement the IN service.

3. SCP interrogates SDP where the Service Scenario of the account is checked and

Charging Analysis takes place. Allowing and Barring Lists are also checked at

this stage.

4. The SDP sends the result of the calculated call duration together with call data suchas announcements to be played, if required. The SCP orders the SSP to play

SCP SDP PPAS

IVRMSC/

SSP

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announcements if this has been requested by the SDP. Further on the SCP orders the

SSP to setup the call and to supervise it based on the call duration calculatedby the SDP.

5. After the call is ended, SSP notifies the SCP of the call disconnection.

6. A Final Report is sent from the SCP to the SDP. It contains the total duration of the

call as well as the duration for the last period used.

7. If USSD notification is used the SDP will send the USSD information to the HLR forfurther delivery to the subscriber.

Nomenclatures are specific to Ericsson system. It may vary with vendors but basic

functionalities remain same.