Standards Watch : TAP3 Migration Challenges

Although earlier implementations of the TAP (Transferred Account Procedure) standard did not have the wherewithal to handle the nontraditional demands of next-generation wireless services, that shortcoming was not a concern, because most operators were not even close to figuring out what services would take off.

The problem is that many operators have been waiting for the implementation of GPRS roaming before converting from previous TAP formats. Unfortunately, conversions still must overcome a number of issues, and many operators are unaware of the need to implement pure TAP3.

“In essence, a TAP2 operator who upgrades to TAP3 is still a TAP2 operator—and the conversion, which may be complex and costly, negates a great deal of the value inherent in TAP3,” says Christer Gullstrand, chairman of the Transferred Account Data Interchange Group within the GSM Association (GSMA). “Because operators have focused solely on GPRS for quite some time, they have actually created the need for implementing TAP3.”

Gullstrand cites TAP3 support of m-commerce, location services, support of interoperator tariffs, the ability to reprice calls by the home network, support of interstandard roaming, CAMEL and more efficient handling of taxes. “The cost of implementing TAP3 is very small compared to the cost of implementing GPRS, as clearinghouses normally have proprietary solutions to do that,” he says. “Converting from a lower to higher format is much more difficult, so it makes more sense for operators to implement TAP3.”

The wholesale bill has to concur with the retail rate. In other words, operators must reconcile packets and volumes so they can measure how much their networks are taking in compared to how much they are losing.

“You measure kilobytes of information consumed on the wholesale side, but you can’t expect consumers to understand that they are buying so many kilobytes of information when they send a picture from their phone while at happy hour in a pub while on vacation. They don’t want to be surprised at the end of the month with a huge bill,” says Mike Pulley, product manager for telecommunications at AMS. He believes TAP3 is germane now that GPRS is taking off. “Network elements must capture information about quality of service and volumes of packets in order to do proper rating,” he says, “and TAP3 is being updated continuously to allow for elements of the network that are structured to handle new variables and fields inherent in 3G services.”

He notes, too, that TAP3 supports Single Circuit Switched Data, High Speed Circuit Switched Data and GPRS. “Short messaging is complicated enough, as SMSCs, although part of operators’ networks in most cases, add a level of complexity if a roaming subscriber receives an SMS while roaming, or a roaming subscriber sends an SMS while roaming using his home network SMSC,” Pulley says. “With MMSs [multimedia messaging], network elements will have to handle even more complex data.”

ASN: Answering Conversion Woes?

While the business need is clearly emerging, conversion to TAP3 has been costly and arduous enough that most operators are still using TAP2. Conversions do, indeed, require extensive testing—largely because previous versions of TAP had fixed record lengths, requiring special viewer software.

However, the latest versions of TAP3 are supposed to differ from their predecessors by having no fixed and rigid standards, or size limitations or constraints. “In other words, the GSMA is working to make TAP3 a standard that can be readily expanded for new or existing services,” says Gullstrand.

Because TAP3 is based on ASN.1, a flexible encoding mechanism that enables operators to use commercial tools for expanding and converting from older versions of TAP, TAP3 should be significantly more adaptable and contain significantly more information.

However, some critics say the ASN.1 format is not readable from a text editor, making it rather complex to build perfect TAP3 files. Some say that because earlier TAP formats were ASCII-based, they were much easier to edit and view.

“Indeed, you cannot edit or read TAP3 files without a tool,” says Gullstrand. However, he notes, the GSMA supplies the TAP Testing Toolkit (TTT), which enables operators to view and validate TAP3 files.

“There are also plenty of TAP3 editors available that enable you to modify the contents of TAP3 files,” he points out. “If you don’t have access to a tool, it is of course easier to handle TAP files prior to TAP3; but it is really not a problem with TAP3.” Gullstrand says operators need a tool anyway, as most roaming files are very large, sometimes comprising tens of thousands of call events, which makes printing or handling files arduous without a tool.

A Little R&R

The latest Release of the TTT, under the Returned Accounts Procedure (RAP), was introduced in April 2001 to TAP3.2 to enhance “Rejects & Returns” (R&R) to address the fact that operators were losing revenue when individual erroneous call event details were rejected. With previous TAP version, an error concerning a single call in a TAP file blocked the entire file and delayed the data of all the other calls.

“Under TAP3, the home network will validate incoming TAP transfers and reject call event details that do not conform to the TAP standard or to the terms of the agreement,” explains Gullstrand. “RAP rejects only bad calls, rather than entire TAP files, as in the past.” That means all errors and incorrect call event details are corrected and resubmitted to the visiting network. Resubmitted RAP files are automatically deducted from financial records and settlement records, so the visiting network can recoup roaming revenue from the home network for corrected, resubmitted TAP files and call event details. That enables good calls to be billed immediately, rather than having to wait for bad calls to be corrected and returned.

“Now, the R&R process enables operators to deliver fewer call event details in the reclaims process, making for a simpler invoicing process, which may facilitate future net settlement requirements,” Gullstrand says. “It also supports nonstandard validation checks, which may have been agreed bilaterally between roaming partners, not to mention reducing administration costs previously involved in error handling.”

Interoperator Tariffs

TAP3 also handles all features of the interoperator tariff (IOT), such as home public land mobile network (HPLMN) repricing and call level discounts. “With full support of the IOT, it enables home operators to verify the IOT of the VPMN [visited public land mobile network]. The VPMN can give call level discounts, and the HPLMN can then verify that the discounts have been correctly applied. Without being affected by any discount program or call levels being charged by the VPMN, the HPLMN can then easily reprice each call according to his own tariff,” explains Gullstrand. “Factoring in call level discounting schemes and network repricing by the home operator enables operators to bill roaming customers for all GSM Phase 2+ services.”

Being able to price roaming independently of where the roaming subscriber travels will also prevent lost revenue due to another operator’s discounted pricing schemes, says Gullstrand. CAMEL

Customized Application of Mobile Enhanced Logic (CAMEL) Phases 1 and 2 are supported in the current version of TAP3. CAMEL Phase 3 is supported in TAP3.4. Very few implementations of CAMEL are live today, but this is starting to change, as prepaid and roaming customers are becoming increasingly more important to operators. One particular issue impacting the wider uptake of CAMEL is that an individual network operator cannot use it in isolation—both networks in the roaming relationship must have CAMEL for it to work.

Enhanced Marketing and Customer Care

The basis of TAP3 is that it contains information detailing where a call was initiated and where it was terminated. This helps create a profile of customer behavior patterns, which is essential information for 3G marketing and customer service functions. “Building up a picture of where your customers roam and where they call while roaming is highly useful to focus marketing efforts for these services, and provides a lever to use when negotiating better deals with roaming partners,” notes Gullstrand. He believes such information can be used to construct a specific demographic profile of the customer base and permit a high level of accuracy in targeting individual customer segments. “Within the customer care remit, the levels of service can be determined and enhanced by measurement of the number of dropped or incomplete calls,” he says.

The Future?

The GSMA has started discussions with other groups and associations to broaden the reach and applications of the TAP standard. Currently it is in talks with the IPDR.org (Internet Protocol Detail Record Organization) and the WAP Forum to ensure that the TAP standards do not operate in isolation.

“Each biller is different, but they will need TAP if their pipes are going to talk to others with GPRS services,” says Pulley at AMS. “If everyone tries to set up their own standard or individual agreements with each roaming partner, it’s going to be impossible. People want to send weather reports, maps, pictures, and ultimately video via their phones. Operators need to prepare now.”|