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Why All Roads Lead to Roam

By Gary Drouillard

Competition in the North American roaming market is forcing cdmaOne operators to look further afield to boost revenues, with international coverage moving higher up the agenda. The legacy of past numbering systems is, however, making things difficult. Gary Drouillard, ICO Global Communications.

Wireless operators in North America have successfully and widely deployed cdmaOne systems throughout their coverage areas. In roaming mode, cdmaOne handsets have found acceptance on the networks of different operators.

Roaming administrators have faced no changes to roaming agreements or other adjustments which could hinder seamless operation. The handsets and base stations have negotiated the connection automatically across the digital air interface, while other operations such as roamer validation and call delivery have been carried out in the background.

However, while things may have been without complication on the technical level, on a higher level, things are not so straightforward. The relative calm of a duopolistic marketplace has been shattered with the arrival of the PCS upstarts, and the markets are in a state of confusion as operators adjust to the changing dynamics.

The race for market share may degenerate into a race for the bottom line as operators offer lower and lower airtime prices. It could become a question of who can sell the cheapest minute and still stay afloat.

If an operator chooses not to go down this road it will need to look for ways to differentiate itself, and coverage may be one choice. Operators with large, national footprints have a strong advantage here, and we are already seeing them play this card.

A number of rate plans that apply a flat rate or a home rate plan from coast to coast are being offered. Some of the major operators are even offering air, toll and roaming charges rolled into one low per-minute rate. This effectively eliminates roaming and long distance charges as customers have seen in the past. Operators that offer a 'one-rate' plan but do not have national footprint will need to exert tremendous pressure on their roaming partners to reduce roaming rates. And that's exactly what we are seeing today.

Roaming rates are now typically less than half the level they were just two years ago. Daily access charges are also being abolished. The end result is that even with healthy 30­40 per cent annual increases in roaming volumes, the lower prices have caused significant drops in net roaming revenues.

Pressure points

These two pressure points - the need for differentiation and the need to find new sources of revenue - are causing operators to look to international roaming as a possible solution. The question then is whether cdmaOne operators are in a position to carry out international roaming.

Hutchison Hong Kong and BC Tel Mobility in British Columbia have shown that it is possible for North American carriers to reach overseas to link up with new roaming partners. The record shows, however, that it is not easy. Firstly it requires a highly motivated and adept overseas participant which is willing to play the game by North American rules: join a U.S. clearing house; use North American validation, fraud monitoring and call delivery mechanisms; and pay in U.S. currency. Secondly, it requires much persistence on the part of the overseas operator to gain the attention of US-based carriers and get them to sign roaming agreements.

The key reason for the reluctance of North American carriers to reach south to Latin America or to Asia Pacific where there are compatible air interface standards, is numbering scheme difficulties. Historically, the three most prominent air interface standards in North America - analog AMPS, CDMA and TDMA - all share a common ancestor, the Advanced Mobile Phone System developed in the early 1980s. What may have been considered advanced at that time, is now showing its age. Whether through lack of foresight or ambition, AMPS was sized only for North American or for single-country usage.

The AMPS numbering approach was modeled on the North American Numbering plan. The scheme, with the standard format of NPA-NXX-XXX (Area Code + Central Office + Line Number), was designed as a numbering plan for North America, and made no provisions to prevent the same numbers from being used in other parts of the world. In practice, the same phone numbers are being used in other countries, a situation which could cause confusion. Fortunately, the International Forum for AMPS Standard Technology (IFAST) is trying to sort out this part of the problem. One principal role it is playing is the coordination of assignment of International Roaming MINs (IRMs) to prevent conflicts with Area Codes.

The numbering problem does not, however, end there. The AMPS standard was mandated using 10-digit cellular phone numbers which were indistinguishable from regular business or residential line numbers. There was nothing inherent in the number to identify it as cellular, or more importantly to determine to which home network it belonged. Before any roaming airtime could be sold, every cellular network was first required to ask who owned the customer and where it should go to confirm that the customer was still valid.

To validate home customers and mobile roaming users quickly and automatically, every operator is forced to keep its internal switch database tables up-to-date with every new line range - all of its own line ranges plus those of its roaming partners. Given that up to 150 roaming partners may be needed to provide complete coast-to-coast coverage, that each of these partners can have hundreds of line ranges, and that new line ranges are introduced every day, it is a considerable task.

The switch table containing this database of numbers quickly becomes very large. Is it any wonder, then, that roaming administrators are overwhelmed by updates? It is simply not practical to ask an administrator to make room in its switch table to accommodate the thousands of line ranges from China, Korea or Australia on the off-chance that someone may actually show up from there.

To its credit, when the Groupe Speciale Mobile sat down to define the Global System for Mobile communications (GSM) standard, it addressed this issue head-on. The ensuing numbering scheme anticipated the involvement of many countries.

Validation request

GSM mobile numbers come with an all-important prefix which identifies both the home country and the network code. This numbering scheme uniquely defines each operator. Visited network operators need only signal back to the home network address, leaving the home carrier to sort through the rest of the line range to complete the validation request.
The big benefit for GSM operators is that they need never concern themselves with individual line ranges or any line range additions in the future. In practice, whole countries can be connected almost instantly, greatly expanding the coverage area with minimal ongoing table maintenance.

How, then, can North American-based carriers overcome the limitations of their AMPS-based legacy? The obvious answer would be to switch to an expanded 15-digit mobile number which would have the intelligence to point to its home network in the five-digit prefix to the line number. This is what the International Mobile Subscriber Identity (IMSI) number would accomplish. In practice, however, asking operators to change all their billing and signaling systems to handle the expanded mobile numbers is a monumental task which to most operators is a non-starter.

A more novel solution may come from something which causes many carriers a major headache - local number portability. Currently the Mobile Directory Number (MDN) and the Mobile Identity Number (MIN) are intertwined. Once local number portability is implemented, however, there will be a separation of the mobile directory number - the public number which acts more as a label than an address and which customers can carry with them from network to network - and the mobile identity number which is retained by an operator and is the number broadcast by the phone and used for routing.

Under certain conditions, a database look-up will need to be carried out to determine who owns the MIN and how to route a call for delivery. Perhaps the conditions which cause a database look-up could be expanded to accommodate situations where roaming users who are not currently in the switch tables show up. The database look-up could supply the routing information for validation and circumvent the need for each operator to maintain table entries for all the line ranges of its roaming partners. This is a possible solution that needs more thorough investigation.

Beyond numbering issues, there remain challenges with regard to network connectivity, roaming agreements and settling on the billing data.

Fortunately, several world expert organizations have banded together to offer a solution to these problems. GTE Telecommunications Services Inc. (GTE TSI), CIBERNET plc and the CDMA Development Group (CDG) have pooled their resources and experience and now offer an international roaming solution called cdmaConnect.

GTE TSI has a variety of solutions in roaming interoperability, data clearing, fraud management and online visibility tools to monitor the usage and location of customers roaming. CIBERNET plc brings its expertise in roaming-related financial services including invoicing, foreign exchange and funds transfer as well as debt collection. The CDG facilitates the gathering of like-minded carriers and can provide a sample roaming agreement and other proven support.


Mobile Satellite Service (MSS) operators may also have a role in reaching a solution. Globalstar, Iridium and ICO are due to provide global coverage over the next two years. There are plans to deliver inter-standard connectivity to accomplish international roaming. MSS operators may do this by either using multi-band, multi-mode 'world-phones' or by using bridging services to connect the different air interface islands around the globe.

Another possibility is that an MSS operator might suggest that customers for whom cost is not a major consideration could use the phone in satellite mode everywhere and forget the various signals of the earth-bound operators altogether. If they are successful in providing international travelers a simple and effective solution, a very lucrative market segment may flee their terrestrial masters and find a new home on the satellite networks.

And the future? Setting artificial boundaries based on geopolitics or technology constraints is inconsistent with the promise of wireless communications. This point is not lost on cdmaOne operators. Their experience and success with cdmaOne will give them the momentum needed to reach a solution.

Gary Drouillard is the IS-41 Roaming Manager for ICO Global Communications, a mobile satellite service provider which aims to begin service in the year 2000.