Checking Out Prepaid Options

It's no secret that prepaid is in a state of rapid growth. The number of U.S. prepaid subscribers will explode from 2.5 million in 1998 to 9.4 million in 2000, according to Northern Business Information, and 30 million, or 21% of the total wireless subscriber base, by 2007, according to Global Marketing Prepaid Strategies. Prepaid offers an enormous potential market to wireless carriers. Understanding the options and technology choices will determine how much and how fast you will realize that potential.

Today's prepaid legacy solutions include prepaid phones purchased at distribution centers and programmed to track users' balances, and the metered billing option. Both have shortcomings. In metered billing, for example, there is no real-time call monitoring. You can update the user's balance only after the billing system processes the call-detail records in batches. Meanwhile, the user's balance can deplete, which means additional costs as you try to recover the balance from the user and handle his customer-care inquiries.

Currently, point solutions based on a service node, an adjunct fitting next to the MSC, address these shortcomings. Calls route to the adjunct, and the adjunct places a second call to the dialed digits via the MSC, bridging the call (called hair-pinning) at the adjunct. These point solutions typically are trunk-based, so the trunks and the voice ports must stay open for the call's duration at the adjunct as well as the MSC. This method causes inefficient network resource use.

Most of today's point solutions are based on service-bureau offerings, and each call to the network is trunked to the service bureau for account validations and cost computations, then routed back to the network. Carriers pay a lot for these calls and must compensate the service bureau for additional charges based on minutes of use. As you grow your prepaid network, service-bureau costs can become unaffordable.

As an alternative, some carriers have established their own platform point solutions. As call volume grows, however, you must expand the number of trunks that hook up on the network and the adjunct sides. You have to add more boxes to increase the capacity. Such point solutions either are not scaleable, or scaleable only at great expense. Most carriers currently do not provide prepaid extensively, because they can't provide seamless roaming and because of implementation difficulties with incoming calls when customers roam.

EMERGING IN PLATFORM SOLUTIONS As another alternative, you can place IN applications on network server service control points (SCPs), with call setup done through signaling instead of tying up a trunk during call setup. Limited-capability switch triggers already are available in IS-41C standard, though just for origination triggers right now. Still, without mid-call operations, the platform has no control if the user's balance approaches zero. No signaling method informs the MSC to play a low-balance warning tone or even to disconnect the call.

Vendors are coming up with interim methods that you can implement through the SS7 network; the ISDN User Part (ISUP) loop-around technology for switch-independent implementations is one. The trunk loops around at the MSC, then the ISUP signaling channel is used on the SS7 network -- ISUP call-setup signaling -- to inform the MSC when a call originates. When the call is answered, the call-setup signals become available in ISUP signaling to tell the IN platform that the call is answered. When the call disconnects, that message also can be sent. There are ways to address low-balance warning with this implementation; however, you still end up tying up low-cost, loop-around trunks on the MSC side as well as voice ports at the MSC in this scenario.

Vendors also are implementing the switch triggers needed for prepaid wireless, but the application can work only with the specific MSCs because prepaid is not yet standardized.

PREPAID STANDARDS Prepaid requires standard triggers that work in a multivendor environment. First, it needs an origination-trigger standard. An origination trigger can interrupt the call processing for a moment and send that call to the IN platform, where the application can check if the subscriber is valid and whether he has enough money to process the call. Then it informs the switch whether or not to process the call.

Prepaid also needs a termination trigger. Today there are termination triggers available that are directed only to the HLR and can't direct to any other SCP application. The MSC needs to interrupt call processing and query the SCP IN platform, which looks at the balance and tells the MSC to terminate.

Prepaid also requires mid-call operations. Here the application maintains the balance and does real-time rating. It has to determine when the balance is low and inform the MSC to warn the user. The SCP instructs the MSC to perform this mid-call operation, and it plays the warning to the mobile user, not the other party. Standards are defining the warning as a whisper warning or warning tone. When the balance is zero, the SCP instructs the MSC to tear down the call.

Prepaid also needs timing triggers. When a call is answered, the platform must know when to start counting. With a mobile-originated call, the MSC interrupts call processing to get instructions from the platform about what to do with the call. The MSC tries to ring the called party, then the call is set up. The MSC informs the prepaid application that the call has been answered, and the counter should start, or it updates the balance when the call ends.

The WIN Phase 1, or IS-771 standard, was approved in 1Q99. This standard expanded origination-trigger capabilities and added the termination trigger and mid-call operation. The mid-call operation is restricted because it is designed for call redirection where the digits to be directed are mandatory. This standard also added flexibility to trigger-addressing mechanisms.

ANSI currently is working on the WIN Phase 2 prepaid standard. The UWCC has created current recommendations for prepaid charging, defining scenarios and proposing triggers that would allow prepaid to work in the ANSI-41 environment. WIN Phase 2 standards should be finalized by early 2000, which means that carriers will have to wait before vendors can implement standardized triggers on the MSCs.

SEAMLESS MIGRATION Migration from trunk-based to switch-trigger-based solutions can occur in phases. If your business strategy dictates a plan to tap into the market early on, you should proceed in steps, rather than migrating directly to a total standard or a vendor-specific trigger-based solution. Additionally, you can choose to implement switch-independent interim solutions that protect your investments.

You also must decide what mix of technology you need. If you plan an immediate deployment, you will have to implement interim solutions and then migrate to the standard. If your network is dominated by a specific vendor, and that vendor supports prepaid triggers with some extensions, you may prefer to implement those. The ideal situation is to create a hybrid solution that can work with multivendor MSCs.

One advantage of implementing vendor-specific triggers is that you can see how prepaid functions with the triggers and get comfortable with the technology before implementing standard triggers when they become available. Network operators will have time to trial the network in some markets, then migrate to standard solutions that can interoperate among vendor MSCs.

Migrating toward trigger-based solutions will free trunks during calls and use those trunk resources for other calls, reducing network investment for trunks and T1 voice ports on the MSCs, as well as prepaid platforms. If you implement a total point solution, you may realize later that a lot of network equipment is underused.

If you migrate segments of your subscriber base, you can migrate smoothly to a standard solution, replacing the call-control interface without affecting caller features. Keep in mind that there are trigger conflicts between multiple IN services such as prepaid and wireless virtual private network. Some vendors are implementing service interaction manager (SIM), which resolves this conflict. The MSC will send the origination request to the SIM on the IN platform, and the SIM will mediate the response from multiple services and reply back to the MSC.

Today's interim solutions can provide prepaid roaming, but they still require trunk usage for backhauling calls to the home network, which ties up voice resources. Certain features required to do that may not be available in all the partner switches or may impose additional provisioning restrictions. But triggers allow seamless, transparent roaming across carriers' boundary lines. The out-of-network MSC can directly query SCP/prepaid over the signaling network. In-network MSCs can query partner network elements directly over the signaling network.

The challenge for carriers will be getting all the MSC vendors to support the standard triggers at the same time. A solution could be to have triggers on specific MSCs or to serve parts of the network using interim solutions such as ISUP.

The market will not wait for prepaid technology, so carriers will find other ways to serve their customers. If you are not the first, somebody else will take advantage of existing technology to capture market share with an interim, vendor-specific or hybrid solution. You should base your decision on your existing need and your anticipated network growth, then choose scaleable, evolutionary solutions that protect your investments.