Streamlining Prepaid

Two of the most popular topics among wireless telecommunications executives today are prepaid service and wireless intelligent networks (WIN). Until now these two topics have been discussed in isolation. However, recently the two technologies have converged, and operators are beginning to deploy true WIN-based prepaid service within their networks. This new breed of prepaid solutions offers the synergy of the WIN architecture and prepaid service, providing wireless carriers with a more cost-effective, expandable prepaid product.

IN THE BEGINNING The wireless industry's first generation of prepaid service solutions was based on collecting call detail records (CDR) or toll tickets from the wireless network. They were relatively quick and inexpensive to deploy because they did not require any changes to the voice network, only a data link from the network to the prepaid platform.

Because a wireless network typically does not release a CDR until after a call is completed, these were post-call solutions. And because the wireless industry was in its infancy with PTT-owned monopolies or private duopolies that had healthy subscriber growth and penetration rates, carriers did not recognize prepaid's value. It was a "service before its time" and was met with limited success.

Handset-based prepaid technology closely followed the CDR-based solutions. Although popular in the European GSM markets through applications that run on SIM cards, concerns over potential fraud exposure, inventory requirements and lack of flexibility have slowed acceptance by U.S. wireless carriers. Handset-based prepaid has been predominantly deployed by resellers.

SECOND GENERATION The second-generation prepaid solutions, referred to as trunk-based or adjunct switch-based solutions, provide an answer to the post-call problem, enabling carriers to deploy real-time prepaid service without any financial exposure. This is accomplished by implementing an adjunct switching platform in the voice network, connected via standard T1/E1 trunks. Blocks of numbers are set aside for prepaid subscribers and as calls originate or terminate for one of these numbers, the network routes the call to the adjunct switching platform. The call then can be controlled by the adjunct switch in real time and torn down once the subscriber has depleted his balance.

Trunk-based prepaid services account for the majority of both domestic and international installations and are being deployed as both a service-bureau and licensed solution. Even though this newer generation of prepaid technology provides the carrier with advantages over the CDR-based services, carriers still are looking for more cost-effective, expandable products. Trunk-based solutions do not make efficient use of the existing network resources because call setup time is increased, and in many cases a call requires up to four ports on the existing wireless switch.

Because the adjunct switching platform carries the voice during the entire call, the number of T1/E1 trunks and associated ports on the adjunct switch required to support a carrier's prepaid subscriber base grows proportionately to the number of prepaid subscribers. A typical domestic model of two calls per day, two minutes per call would require one voice channel for every additional 60 subscribers. For those carriers that have to route the calls over long-distance trunks, the cost becomes even more prohibitive. Another operational issue concerns dedicated numbers. Because prepaid numbers must be blocked in the wireless network to route to the adjunct switching platform, it is not possible to move a credit-based subscriber to prepaid service and still retain the same mobile number.

Last, because the only information that the adjunct switch platform has for rating the call is what is carried within the T1/E1 trunk signaling, the rating granularity level does not match that of the carrier's credit-based billing system. The serving cell-site location for a given call is not contained within standard trunk signals and, consequently, forces the prepaid platform to rate the call only based on generic information, such as which trunk group the call was delivered on. This makes it difficult to implement rating or billing areas in the network that closely match those set up for the regular billing system.

WIN-BASED SOLUTIONS The newest generation of prepaid products is based on the WIN architecture. Functioning as an SCP in an SS7/C7 network, a true WIN-based prepaid platform tells the existing wireless network how to handle and control the prepaid call without the need to route the voice to an adjunct switching platform. The distinguishing feature of a WIN prepaid service is that it does not carry the voice traffic. This is important because some services have been advertised as an "IN" or "WIN" prepaid solution, despite the fact that they still require the voice to be routed to an adjunct switch.

In the WIN architecture, the network generates triggers at various points within the call model, and the prepaid platform answers the triggers with instructions on how the network is to handle the call. These instructions may include such options as allowing the call, providing low-balance warnings to the subscriber, denying the call or providing "whispers" to the prepaid subscriber, alerting him to the end of his prepaid minutes. In all cases, the existing wireless switch is left to do what it does best -- switch and control the call. The SCP prepaid platform provides the intelligence to determine how to process a prepaid call properly.

Advantages of WIN architecture services are that the call setup time is the same as a regular call, and any given call requires only two ports on the wireless switch, resulting in more efficient use of network resources. Any number can be set up as prepaid because prepaid numbers do not need to be blocked. WIN prepaid solutions also offer a finer level of rating granularity. Because the WIN triggers contain both the switch ID and cell site, the WIN prepaid platform can rate calls at a level of granularity that can match or exceed the capabilities of the carrier's credit-based billing system.

The greatest benefit to the carrier is the lack of a required adjunct switching platform, which means the service is more cost-effective, manageable and expandable. As the carrier grows its prepaid business, the associated expansion costs grow at a slower rate. Using the same domestic model of two calls per day at two minutes per call, only one SS7/C7 link pair (two channels on a T1) would be needed for every 250,000 additional subscribers, in contrast to 60 subscribers per voice channel on a trunk-based solution.

WIN PREPAID'S FUTURE So where do prepaid solutions go from here? One certainty is that wireless prepaid service is here to stay. It has been established as a strategic growth weapon for carriers. As WIN standards evolve, you can expect to see more infrastructure providers work closely with billing vendors in fully integrating prepaid service into existing WIN platforms, making prepaid simply another WIN service that can be deployed easily.