Prepaid Billing Technologies-Which one is for you?

As wireless service providers continue to look for new ways to increase revenues, reduce expenses and improve customer satisfaction, they give more and more attention to prepaid service. Enabling additional market penetration and improving operational efficiency, prepaid wireless service has become a powerful tool to help carriers improve their growth rates. In the international markets, prepaid service almost has become a necessity as startup operators struggle with how to provide service in developing countries that have poor mail distribution and no credit monitoring systems.

Prepaid Service-A Billing Technology

To implement prepaid service, wireless carriers need to sort through the variety of available technologies and decide what makes the most sense for them, both from a network infrastructure and billing perspective. Because the actual service provided under a prepaid offering is fundamentally the same as that provided under credit based offerings, the actual enabling technology is tied more closely to the billing of the service rather than to the delivery of the service. Here's a review of these technologies.

Different types of prepaid solutions exist; however, they rely on four different types of technology: handset-based, event/CDR-based, adjunct switching platform-based, and Wireless Intelligent Network (WIN)-based.

Handset-Based

Handset-based prepaid billing solutions do not require changes or modifications to a carrier's infrastructure. All the necessary technology is deployed through intelligence built into the handset (or added through the introduction of a computer chip). In GSM markets, this is implemented through the use of a SIM card or smart card. As a subscriber uses the phone, the handset meters the usage against a stored rate plan and account balance, ending calls upon depletion of the balance. This solution technology has not gained wide acceptance. The need to inventory special or modified handsets, the difficulty in changing rate plans, and the need for a physical connection to be made to the handset (or SIM card) in order to replenish the balance or units available to the subscriber has steered most carriers away. This solution, however, has become widely deployed within the reseller channel because it does not require any changes within the carrier's network.

Event/CDR-Based

Event/CDR-based prepaid billing solutions use the CDRs produced by the wireless switch to rate the prepaid subscriber's usage. They react accordingly. At the heart of these solutions are real-time data collectors/routers used to transport the CDRs from the switch to the prepaid billing application server. As a subscriber uses up his or her available funds, the prepaid application provisions the network to hotline any further calls to an IVR in order to receive an automated announcement indicating that the funds are low or depleted. The same IVR is used by the subscriber to automatically replenish his or her account using a prepaid phone card (obtained through a retail distributor), a credit/debit card or through a electronic funds transfer direct from their bank account.

Commonly known as a "post-call" solution, because any required actions (warnings and service denials) take place after the call is complete, it has had a mixed reception. There is a "one call exposure" concern because a subscriber can place his last call and stay connected while his account balance becomes negative. This occurs because most wireless switches do not release the CDR until after the call has ended. In practice, however, carriers deploying these solutions have had few problems. They have guarded against such exposure through proper setup of the processing thresholds used to determine when to warn and deny service to a subscriber and through the use of appropriate call barring classes.

Users can generally find easier ways to defraud the carrier than to pay for service activation, purchase prepaid airtime, make enough calls to bring the balance close to zero, then make that 3-hour call that overruns their account.

Event/CDR-based prepaid billing solutions are cost effective because they do not require major changes or modifications to the wireless network infrastructure. In most cases the carrier already has real-time data collection/routing capability in place. It feeds CDRs to its credit-based billing application. For those carriers that do not have adequate capabilities, the addition of such a real-time data system has benefits beyond those of the prepaid service. These benefits include real time applications such as credit monitoring, fraud monitoring and more up-to-date customer information.

In response to carriers' desires for real-time billing data, infrastructure providers are providing the capability for their switches to create CDRs at call setup, and in some cases, periodically throughout the duration of the call. Additional features are being implemented that allow external applications to instruct the wireless switch to terminate a given call. These new features will eliminate the concern over the "one call exposure" and enable what is referred to as an "in-call" solution, allowing the prepaid application to monitor and terminate the prepaid call appropriately.

Adjunct Switch Platform-Based

Adjunct switch-based prepaid billing solutions are the most widely deployed prepaid solution in the market today (see Wireline Prepaid Solutions sidebar). Although this solution comes in many different flavors, the approach is always the same - extend the existing network infrastructure with an adjunct switching platform. Based upon the fact that most of the major infrastructure providers have predefined call models within their distinct switching architecture, carriers have moved to implementing adjunct switches in their network, controlled by external applications like prepaid billing. The adjunct switch is usually connected to the network using standard T1/E1 trunks assigned to a particular block of prepaid numbers. As the prepaid subscriber places a call, the network identifies the call as a prepaid call and routes it to the adjunct switch via one of the T1/E1 trunks. As the adjunct switch receives the call, it queries its database to verify that the subscriber is active and has a positive balance. It plays any required announcements to the subscriber, and it routes the call to the PSTN or back to the wireless network, based upon the subscriber's dialed destination. Since the prepaid adjunct switch is directly in the call path at all times, it provides for "pre-call" control allowing the platform to monitor and tear down the call if necessary.

Implementation of this type of solution is generally done using either true matrix or computer telephony interface (CTI) types of switching platforms. CTI-based switching platforms are generally built using PC processors and CTI voice processing cards, providing for a cost-effective solution for small installations. Matrix switching prepaid platforms, built using programmable switches (major suppliers include Excel, Summa Four and Harris) coupled with a Unix or PC-based prepaid application server that controls the switch, provide for larger, more cost-effective solutions.

Because each prepaid call in progress requires two ports on the adjunct switching platform and up to four ports on the wireless switch (for mobile-to-mobile calls), the incremental costs associated with expanding the platform's capacity can become cost prohibitive. In addition, depending on the network's size and solution configuration, if the voice load needs to be hauled over long-distance lines to or from the adjunct switching platform (such as would be needed to support roaming), the cost can rise quickly. This concerns international carriers with many costly long-distance lines. Despite these drawbacks, this solution is still the most popular prepaid technology.

New Generation WIN-Based Prepaid Solution

The latest generation of prepaid billing solutions is based upon the IS-41 standard or Wireless Intelligent Network (WIN) concept. WIN-based prepaid billing offers the real-time "pre-call" control capabilities as adjunct switching platform solutions, without the need to be in the call path and carry the voice load. This eliminates the need for additional voice trunks and allows efficient use of the wireless network because the wireless switch handles all the call routing and control.

How Does WIN Prepaid Work?

The WIN-based prepaid billing solution platform is a Service Control Point (SCP) communicating with the wireless network through an SS7/C7 signaling network. The SCP interacts with the network at different stages of a prepaid call through the use of WIN triggers. Under the WIN call model, the network generates triggers at different points in a call's life cycle, allowing the prepaid application to interdict and make decisions about how that call should be processed.

How does a call work? A subscriber dials a number and presses SEND. The wireless network sends a WIN call-setup trigger to the prepaid platform, indicating the subscriber's name and location as well as the destination of the call. The prepaid platform receives the message, queries its database and sends a response message back to the network directing it on how to process the call. At this point in the call, there are several options the prepaid platform could instruct the network to perform:
deny the call
route the call as dialed
play a recorded message, then deny the call
play a recorded message, then route the call as dialed
route the call to an IVR (for a customized message), then deny the call
route the call to an IVR (for a customized message), then route the call as dialed. The option selected by the prepaid platform is based upon threshold processing parameters within the prepaid billing system set by the carrier. In the event that the prepaid platform instructs the network to route the call as dialed, a countdown timer is started based upon the allowable talk time calculated from carrier-defined threshold parameters, the subscriber's rate plan, dialed destination, time/date and current balance.

If the countdown timer ends before the subscriber terminates the call, then the prepaid platform instructs the network to terminate the call. In any case, once the call is released, the wireless network sends a WIN call-release trigger to the prepaid platform indicating the ending time of the call. The prepaid platform receives the call-release trigger, rates the completed call and updates the subscriber's balance accordingly.

WIN Prepaid Billing
Centralized Prepaid Platform

Since all the WIN components are connected via the SS7/C7 network, the prepaid platform can be located centrally, without the need to haul the voice traffic off the switch.

More Efficient Use of the Wireless Switch

In the WIN model, the switch is off loaded of service control processing and handles only the switching function. This function resides exclusively in the wireless switch, not in any adjunct platforms, resulting in only two ports being used per prepaid call on the switch.

More Cost Effective Expandability

Expansion of the WIN prepaid solution is similar to the adjunct switching platform solution in that it leads to increases in processing power, RAM, I/O, storage, among other improvements. However, instead of increasing T1/E1 ports, SS7/C7 links are added. This is a significant difference. Because the adjunct switch solution is in the voice path, it is very susceptible to any increase in the number of minutes of use, either through increase in subscribers, calls per subscriber, duration of calls or any combination of the three. In the case of the WIN prepaid solution, only an increase in the number of calls has any impact on the number of links required. The cost of one SS7/C7 link is greater than the cost of one T1/E1 port; however, the overall cost for a given capacity is less (i.e., 1 SS7/C7 link can handle many more calls per hour than one T1/E1 port). The expansion cost difference between the two types of solutions is substantial, especially on large installations.

Roaming Support

WIN-based technology can facilitate roaming which carries over to prepaid service as well, since roaming partners' wireless networks communicate with each other over the same SS7/C7 network.

With wireless service providers trying to acquire new subscribers and retain existing ones, the ability to differentiate themselves by implementing enhanced, distinguishing services for lower costs is critical. Combining these two powerful enablers, prepaid service and WIN, wireless operators are armed with the tools necessary to compete in today's markets.

Andres Arteta is product manager of Subscriber Computing, Inc.'s PrePay Metered Billing Product, which supports both WIN-based and Event/CDR-based technologies. Subscriber Computing also provides customer care and billing, fraud management, and real-time data collection and routing solutions to the wireless communications industry.

Wireline Prepaid Billing Solutions

Beginning in 1982 wireline carriers in Europe and Asia started prepaid telecommunication service. In 1992 it moved to the U.S. This type of prepaid service took the form of prepaid calling cards. Carriers targeted prepaid long distance calling services, generally at public phones. Most recently in the US, this type of prepaid service has become more popular over the last few years as wireline operators, especially long-distance resellers, have become creative in the retail distribution of prepaid calling cards. In many international markets, prepaid calling cards are virtually the only way a non-emergency call can be placed from public phones.

The technology used to support and to charge for wireline prepaid calling card services is similar to that used in adjunct switching platform-based wireless prepaid billing solutions. Almost all of the wireless prepaid adjunct switching platform solution providers started by providing prepaid solutions to wireline carriers or resellers long before they entered the wireless market. Typically, the calling card subscriber would dial a toll free (800 or 888) number, which would be routed by the wireline switch to the adjunct switching platform via standard T1/E1 voice trunks. The adjunct switching platform would prompt the subscriber for their dialed destination, followed by their calling card number. Once the calling card was verified as active with a positive balance, the adjunct switch would play any necessary announcements and then route the call back to the PSTN to the dialed destination. With the platform in the call path, the call could be monitored and torn down if needed at the depletion of the card balance.

Typically these billing solutions tends to be simpler than that of their wireless cousins:
Card-Centric

A key difference of wireline prepaid billing solutions when compared to wireless prepaid billing solutions is that wireline billing solutions are card-centric, whereas wireless is account-centric. The distinction rests in the fact that the wireline carrier knows nothing about the subscriber and that the carrier requires no pre-establish account. A subscriber simply buys a calling card and starts making calls. As soon as the prepaid balance is used, the card is inactive within the system. In wireless prepaid billing solutions, a pre-established account with the wireless carrier is required. Because no information is known about the subscriber, wireline prepaid calling card solutions have virtually no customer care components.

Originating Calls Only

Because no information is known about the wireline prepaid calling card subscriber and because the service is card-centric, a caller cannot receive inbound or terminating calls. The service only supports originating, or outbound calls, which are typically made from public phones. This has resulted in simpler rating engines for wireline prepaid card billing solutions.

No Mobility

As is the case for credit-based service, wireline carriers do not need to address mobility issues. With no mobility, there are no roaming issues to resolve and rating is simpler, thanks to a single point of presence for long-distance rating.

Recent interest in prepaid service has quickly risen with wireless local loop (WLL) carriers. Many of the WLL markets are being deployed in developing countries. In countries that have predominately cash based economies with very little credit monitoring and/or postal services, prepaid service is a natural. An interesting trend has developed. As these systems are being deployed in parts of the world where one phone may service many people, the need to have a card-centric and account-centric billing solution has surfaced. This will inevitably lead to a combined or linked prepaid billing solution that supports both wireline and wireless services from a common calling card.