1. Communication Protocol Engineering Lab. Myung Jo. Kim. 1 Mobile Prepaid Phone Service 2003. 5. 13. Kim Myung Jo (silveraspen@hanmail.net) Communication Protocol Engineering Lab.

2. Communication Protocol Engineering Lab. Myung Jo. Kim. 2 Contents  Mobile Prepaid Services  Wireless Intelligent Network Approach  Service Node Approach  Hot Billing Approach  Handset-Based Approach  Comparison of the Prepaid Solution

3. Communication Protocol Engineering Lab. Myung Jo. Kim. 3 Overview  Traditionally prepaid phone – A telecommunication service that requires a customer to pay before making calls – Public phone (use coin) – Public phone (use prepaid card)  Prepaid telecommunication services – Offered in Europe and Asia in 1982 – Became popular in the United States in 1992 More than 30 prepaid solution vendors are currently competing for carrier business  Mobile prepaid service – Has been growing exponentially all over the world

4. Communication Protocol Engineering Lab. Myung Jo. Kim. 4 Advantage and Characteristic  Service provider – Reduce the business operation costs  Customer – Provide immediate service without the need for long-term contracts Many end users just want to enjoy the service Do not want to fill in subscription forms  Difference of two type of prepaid service (fixed vs mobile) – A fixed telephone service provider knows nothing about the prepaid customers – Fixed prepaid service allows outgoing calls only, whereas mobile prepaid service allows both incoming and outgoing calls

5. Communication Protocol Engineering Lab. Myung Jo. Kim. 5 Mobile Prepaid Services (1/2)  In GSM prepaid service – A customer subscribes with prepaid credit Coded into the subscriber identity module (SIM) card or kept in the network – Initialization of a prepaid customer must be completed within a certain number of days after subscription – If the balance is depleted The customer cannot originate calls Allowed to receive phone calls for a predetermined period – To recover the prepaid service The balance has to be recharged by purchasing a top-up card, which is similar to a lottery scratch card The system verifies and refreshes the account if it is a valid code

6. Communication Protocol Engineering Lab. Myung Jo. Kim. 6 Mobile Prepaid Services (2/2)  Mechanism in the mobile prepaid service – An extra billing system for mobile prepaid service is required – A real-time usage metering function must be built in the prepaid service system to monitor the amount of remaining credit on the customer account – Sales taxed are generally collected at the point of sale (POS) for prepaid service – A customer care mechanism maintains items including customer activation and deactivation times, credit value, remaining time period, PIN

7. Communication Protocol Engineering Lab. Myung Jo. Kim. 7 Wireless Intelligent Network Approach  WIN (Wireless Intelligent Network Approach) – A complete solution to prepaid service – A P-SCP (Prepaid Service Control Point) communicates with the M SC through SS7 signaling network – Several WIN triggers are defined – All billing information for a prepaid customer is stored in the P-SCP

8. Communication Protocol Engineering Lab. Myung Jo. Kim. 8 WIN Call Origination

9. Communication Protocol Engineering Lab. Myung Jo. Kim. 9 WIN Call Termination (called-party-pays billing)

10. Communication Protocol Engineering Lab. Myung Jo. Kim. 10 WIN Prepaid Recharging

11. Communication Protocol Engineering Lab. Myung Jo. Kim. 11 Service Node Approach (1/3)  The service node approach – The most widely deployed prepaid service solution at the initial stage of prepaid service provisioning – To deploy the prepaid service without interrupting the existing call models Most mobile service providers implement service nodes in their networks to externally control prepaid billing – The service node is implemented using CTI (Computer Telephony Integration) techniques and PC-controlled PBX (Private Branch Exchange) – The same platform can be used to implement the prepaid service node effectively

12. Communication Protocol Engineering Lab. Myung Jo. Kim. 12 Service Node Approach (2/3)  CTI – Utilize computer intelligence to manage telephone calls – APIs (Application Programming Interfaces) TAPI (Telephony Applications Programming Interface) TSAPI (Telephone Services Application Programming Interface) – Support general APIs that allows fast deployment  PC-controlled PBX – The software (C++) in the call control layer can be modified to implement various telecommunication applications – Provide larger and more cost-effective solutions than CTI switching

13. Communication Protocol Engineering Lab. Myung Jo. Kim. 13 Service Node Approach (3/3)

14. Communication Protocol Engineering Lab. Myung Jo. Kim. 14 Hot Billing Approach (1/2)  Hot billing – Uses CDRs (Call Detail Records) to process prepaid usage – The prepaid CDR is created in the MSC – The information in a CDR Type of service Date/ time of usage User identification The destination of the call Location information – These records are generated when the calls are completed, and are transported from the MSC to the prepaid service center – The balance of the customer’s account is decremented according to the CDRs

15. Communication Protocol Engineering Lab. Myung Jo. Kim. 15 Hot Billing Approach (2/2)  When customer uses up the prepaid credit – The HLR and the AuC are notified to prevent further service access – The prepaid service center instructs the network to route the next prepaid call attempt to an IVR To play an announcement indicating that the balance has been depleted – The IVR can communicate with the customer to replenish the prepaid credit by using a top-up card, a credit/ debit card, or a credit transfer from a bank account

16. Communication Protocol Engineering Lab. Myung Jo. Kim. 16 Hot Billing Architecture and Interfaces

17. Communication Protocol Engineering Lab. Myung Jo. Kim. 17 Hot Billing Prepaid Service Initialization  Step1 – The customer subscribes to the prepaid service center at the POS or by calling the customer care center  Step 2 – The prepaid service center creates a subscriber data record including IMSI, MSISDN, account of credit, period of validity tariff model, and other authentication-related information  Step 3 – The prepaid service center activates the prepaid service by sending the customer data to the HLR, which then creates a record for the customer

18. Communication Protocol Engineering Lab. Myung Jo. Kim. 18 Hot Billing Prepaid Call Origination

19. Communication Protocol Engineering Lab. Myung Jo. Kim. 19 Hot Billing Customer Query and Recharging

20. Communication Protocol Engineering Lab. Myung Jo. Kim. 20 Handset-Based Approach (1/3)  In the handset-based approach – The MS performs credit deduction during the call and determines when the credit limit is reached – The prepaid credit is stored in the MS In the United States => special phones are required For GSM => the credit is stored in the SIM card

21. Communication Protocol Engineering Lab. Myung Jo. Kim. 21 Handset-Based Approach (2/3)  SIM card issues – Two partitions of SIM memory Dialing numbers, short messages received, a menu of subscribed services Programs that can be executed to carry out simple commands – AoC (Advice of Charge) message To transfer the prepaid balance information and the tariff schemes Provide information for the MS to produce a cost estimate of the services used AoCC (Advice of Charge Charging) AoCI (Advice of Charge Information) – To utilize handset-based prepaid service The MS must support AoCC AoCC is activated for every prepaid customer in an HLR which will be used in call setup and tariff switching

22. Communication Protocol Engineering Lab. Myung Jo. Kim. 22 Handset-Based Approach (3/3)  Data fields in a SIM card – ACM (Accumulated Call Meter) Accumulates the used prepaid units – ACM* (Accumulated Call Meter Maximum) Records the amount of purchased prepaid credit – PUCT (Price per Unit and Currency Table) The value of the home unit in a currency chosen by the subscriber

23. Communication Protocol Engineering Lab. Myung Jo. Kim. 23 Handset-Based Prepaid Call Origination

24. Communication Protocol Engineering Lab. Myung Jo. Kim. 24 Combined Prepaid Call Origination

25. Communication Protocol Engineering Lab. Myung Jo. Kim. 25 Handset-Based Prepaid Recharging

26. Communication Protocol Engineering Lab. Myung Jo. Kim. 26 Roaming  Roaming to other network – To provide roaming to prepaid customers An agreement must be made between the home system and the visit system This agreement is required so that the visited system can distinguish prepaid calls from the postpaid calls generated by roamers Use special MSISDN  Prepaid charging – Cannot be performed at the visited system because the home system and the visited system may exercise incompatible prepaid service solutions  Most networks – Require the visited MSC to route the prepaid call back to the home network

27. Communication Protocol Engineering Lab. Myung Jo. Kim. 27 Roaming to Other Networks for Prepaid Service

28. Communication Protocol Engineering Lab. Myung Jo. Kim. 28 Scalability  The handset-based & the WIN approaches – have good scalability  The hot billing approach – The size of prepaid customer population is limited to the MSC’s capability to process and deliver CDR messages  The service node approach – The capacity of the trunks between the service node and the MSC limits the prepaid customer population that can be accommodated in the system

29. Communication Protocol Engineering Lab. Myung Jo. Kim. 29 Fraud risk  The handset-based – AoC communication is not encrypted – It is possible to modify the credit illegally in the MS  Poor fraud protection  The hot billing approach – The risk of fraud can be high Due to one-call exposure  The service node approach & the WIN approaches – Exhibit low fraud risk

30. Communication Protocol Engineering Lab. Myung Jo. Kim. 30 Initial system setup  The handset-based – Dose not require changes to the mobile network infrastructure, except that the MSC must support AoC – Special SIM software is required to execute rate plans in the MS => Average setup cost and time  The hot billing approach – Requires the integration of the prepaid service center, the IVR recharging mechanism, and the MSC/HLR => Average setup cost and time  The service node approach – The mobile network not modified => Setup time is short and the setup cost is for the establishment of the service node  The WIN approaches – The design of services and switch software development for intelligent network is complex => Setup time is long and setup cost is very high

31. Communication Protocol Engineering Lab. Myung Jo. Kim. 31 Service Features  Handset-based approach – Supports limited service features the number of rate plans that can be stored in the SIM card is limited and cannot be conveniently updated  Hot billing approach – Better than average  The service node & the WIN approaches – Support flexible service features  None of the four approaches can support prepaid short message service – Because the short message is delivered by the SS7 TCAP, which cannot be identified by the MSC – Instead, charging for the short message is done at the SM-SC

32. Communication Protocol Engineering Lab. Myung Jo. Kim. 32 Prepaid Short Message Service

33. Communication Protocol Engineering Lab. Myung Jo. Kim. 33 Real-Time Rating  The handset-based approach – Real-time rating is performed at the MS  The service node approach – Real-time rating is performed at the service node  The WIN approaches – Real-time rating is performed at the P-SCP  The hot billing approach – Cannot support real-time rating – The credit information update depends on the MSC capability of sending CDRs