Pre-Payoff

Thanks to WIN Phase II, you may be able to make your prepaid service more economical for your customers.

Prepaid wireless is increasingly popular, especially to market segments such as youth, who generally do not have credit established, or who are unable to sign legally binding contracts because of their age. One might assume that prepaid has become so popular because it is inherently cheaper. Surprisingly, however, it's an inherently more expensive service in some important ways. WIN Phase II standard TIA/EIA/IS-826 might change that equation and target prepaid as the dominant way people pay for their wireless communications needs.

About WIN

WIN is a concept shamelessly stolen from landline telecom, where similar systems are known as the IN or the advanced IN (AIN). These concepts often are shrouded in academic jargon, but actually they are quite simple. Switching systems are made simpler, and when they need to invoke a capability that they do not support, they invoke a trigger, which initiates a message to a peripheral piece of equipment, usually called a service control point (SCP), which, in turn, responds back with a message indicating actions the switch should take.

The ability to offload a switch is useful when a switch is hitting processor limitations, when peripheral equipment is cheaper, more flexible or can be developed faster, or when a shared database is required. It is not for the faint of heart because messaging must be carefully designed or switch savings soon are lost in a flurry of signaling messages.

Some people believe that WIN will reduce the need for switch-software upgrades once a complete set of triggers is implemented. This, however, is the impossible dream because virtually every new capability requires new triggers, new parameters in trigger messages or novel actions based on the contents of these messages. The current set of triggers is always complete ... until someone thinks of a new service, which cannot use any of the existing triggers.

The WIN effort has not been wasted because the need to off-load switches is important, and this is particularly true with prepaid systems. Prepaid systems can and usually have been implemented without WIN-like capabilities, but these introduce some important costs and have some major limitations. WIN Phase II just might save the day for prepaid.

Quick & Dirty Prepaid

Most existing prepaid systems have been based either on a handset-based model or through the use of peripheral switches. Handset-based systems maintain a counter within the phone, which is reduced whenever calls are made. These systems are particularly prone to fraud, because eventually one of the bad guys will find out how to reset the counter without paying for it (and then sell that information to the others). At first fraud will be zero, then a little, and then overwhelming. Only extremely sophisticated encryption and authentication systems can prevent this.

Network systems are more secure, but less transparent. Prepaid mobiles are forced to make all calls through a special prepaid platform so that the call can be timed, the prepaid account debited, warning tones and announcements provided, the ability to recharge with a credit card offered and, if the account is exhausted, the call disconnected. All these extra trunks and equipment have a cost, and that is partly why prepaid minutes are generally more expensive than postpaid.

Another problem is roaming. If prepaid mobiles are forced to call back to a prepaid platform in their home system, even local calls while roaming involve two long-distance calls. Consequently, many prepaid systems severely limit roaming, which reduces the attraction of the service.

The Ideal

Prepaid systems would be much more flexible if the monitoring could be done without trunking. What if the serving MSC, wherever it is, could send a message to the prepaid platform over the SS7 network whenever a call event occurred, and be assured that the prepaid platform would tell it when the account was exhausted? Wouldn't that be a better system?

As it turns out the masterminds behind WIN Phase II already have designed and published TIA/EIA IS-826 with just this solution in mind.

The WIN Phase II Solution

When any mobile device finds itself in a new system, it performs a registration procedure. If the user of the handset is an IS-826 prepaid subscriber, additional information is transferred, including the type of WIN services supported and which SCP should be used for prepaid operations. When the mobile attempts to make a call, the serving MSC will initiate more complex communications with the prepaid SCP. Because this is a special origination, an ANSI-41 Origination Request will be sent to the SCP to initiate the prepaid transaction, and then a WIN Phase II Analyzed Information message provides enough information to configure the SCP for the call.

At this point, the SCP recognizes that a call has been established but that it has not yet been answered. If the call is aborted at this point, the prepaid account might not be decremented at all. When the SCP receives an OAnswer message (the O meaning origination), it can start decrementing the prepaid account. When the call is over, an ODisconnect message tells the SCP to stop decrementing.

Sometimes, information must flow from the SCP to the MSC. If the balance on the account gets below a certain threshold, the SCP can trigger a low-balance tone or announcement to the mobile through the Call Control- Directive. The same message, with different parameters, can be used to disconnect the prepaid call when the balance is exhausted.

Although WIN Phase II introduces new signaling messages, the prepaid monitoring equipment is no longer in the call path, and no longer needs to incorporate switching equipment. Consequently, as long as the mobile is roaming in a system that has implemented IS-826, when it makes a local call, it truly will be a local call. Although this does not eliminate the additional costs of prepaid, it does reduce them. Reduced costs will allow carriers to make prepaid more economical, and consumers will not think that prepaid systems are highway robbery.

When all the phases of WIN are considered, it has been a mixed blessing. Phase I provided network support for enhanced call screening and voice-activated services based in the network, neither of which has generated as much excitement as expected. WIN Phase II, at least the prepaid portion, finally may have hit the bull's eye.

Although prepaid was the prime motivation for WIN Phase II, it also provides for other integrated billing/switching services, most notably wireless freephone (1-800 calls with airtime charges billed to the destination). Although this idea has been tried before, it had many of the same costs and limitations as pre-WIN prepaid.

Now that WIN Phase II has been published, the WIN group is working on a third phase, which will integrate location information with call processing.

When our WIN standards group hits the jackpot, they will have at least one victory to savor in their retirement and, if all the kinks can be worked out of location systems, perhaps several.