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In any argument over the merits of GSM versus AMPS (even when the term AMPS is used loosely, to cover TDMA and CDMA digital cellular systems compatible with AMPS analog), GSM proponents always gloat over the ‘fact’ that GSM is a world standard and AMPS is restricted to the US and a few other countries. Those ‘few’ other countries amount to over 80 (according to a report in the April 1996 issue of Cellular Business, based primarily on US Dept. of Commerce research)! AMPS is dominant in the Americas, and deeply entrenched in Asia, Australasia and Africa. In countries where AMPS and GSM are battling for supremacy, AMPS often emerges victorious. In Australia, for example, where the AMPS system is supposed to be pulled out in a few years, the AMPS system still has four times the subscribers of all three competing GSM systems! The only part of the world that AMPS has never penetrated is Europe, where GSM, NMT and TACS rule.
That is the good news for AMPS. The bad news is that GSM proponents are right when they criticize the capabilities of AMPS for international roaming. The only truly seamless roaming between AMPS countries is between the US and Canada and, due to their integrated telephone numbering plan, it is not really international roaming. International roaming has two major hurdles to overcome – technical obstacles and lack of communication. To solve these problems, a new organization is riding to the rescue. IFAST, the International Forum on AMPS Standards has a mandate to “facilitate the identification and resolution of technical issues to enable the international interoperability of systems using the AMPS family of standards, resulting in the steady migration toward seamless service.”
IFAST arose from the ashes of JCCR, the Joint Committee on Cellular Roaming, that spent a year discussing and resolving problems with roaming between Mexico, the US and Canada. Because this committee worked informally, but effectively, and restricted its discussions to technical issues, the Mexican carriers, in particular, insisted that the group be opened up to carriers from around the world. The first IFAST meeting, held just after Wireless’96 closed in Dallas, had AMPS cellular carriers from Mexico, Colombia, Brazil, Russia, Canada and the US present. Also present were representatives of manufacturers, network providers and the TIA and CTIA trade associations. Those who attended left enthused about the possibilities of this organization, and promised to persuade carriers from many other countries to attend the next meetings.
IFAST is chaired by Fred Gaechter, who also heads the Bellcore Numbering Consulting Group (formerly NANPA) that manages the allocation of phone numbers within North America. IFAST also has two co-conveners, responsible for administrative aspects: Ed Hall of the CTIA and Bernardo Martinez from Grupo Iusacell in Mexico.
What are these technical issues that bedevil AMPS international roaming?
MIN (Mobile Identification Number) ambiguities arise because the MIN was designed to fit a US/Canadian 10-digit directory number. No provision was made for a country identifier, and there is no MIN allocation authority. Consequently, international carriers have to independently follow their own judgment when assigning ranges of MINs, usually inserting a country identifier in the first two or three digits of the MIN, where US and Canadian mobiles have the area code. To make matters worse, several carriers in the US and Canada have used non-standard MINs for special voice and data applications. The IFAST, in conjunction with TIA standards committee TR-45.2, is trying to gather information on this problem.
As an example of this problem, consider a mobile that registers in Brazil with a MIN starting with the digits 505. It could be from New Mexico (area code 505), from Nicaragua (landline country code 505) or from Australia (mobile country code 505). The long term solution to this problem is the migration to IMSI (see below), but in the short term, IFAST, in cooperation with the TIA and CTIA, can compile and distribute MIN usage information that will enable carriers to head off problems while it is still easy to fix them.
An IMSI (International Mobile Station Identity) is the equivalent of the MIN in GSM systems. Adoption of this 15-digit number to identify AMPS phones will not only solve its own international roaming problems, but also facilitate AMPS/GSM interworking and dual-mode AMPS/GSM phones. The IMSI starts with a 3-digit Mobile Country Code (defined in the ITU recommendation E.212), so there is no question which country each phone comes from. However, IMSI is new, and no analog phones yet support IMSI. This makes IMSI a long term solution, and the role of the IFAST will be to educate carriers about its benefits so that carriers will be prepared to support it when large numbers of phones with IMSI start to become available. In the past year, Mexico, the USA and Canada have developed IMSI assignment guidelines and procedures, one of the first steps in full implementation.
SS7 is the packet-switching data protocol that is used to interconnect most modern telecommunications systems, including most IS-41 networks for AMPS cellular automatic roaming. Unfortunately, there are two incompatible varieties: ANSI SS7 used in the US and Canada, and ITU (formerly CCITT) SS7 used elsewhere. The role of IFAST will be to ferret out information that can assist with the transmission of IS-41 messages from one national SS7 network to another, and to help persuade the ITU to provide support for data communications using IMSI as a network address. Ironically, GSM providers have found that with the first US GSM (PCS 1900) systems being installed, they now face the same international roaming problem as AMPS!
The ESN (Electronic Serial Number) is probably now familiar to most people, as it is central to the crime of cloning. Theoretically, the ESN in each phone should be unchangeable and unique. While changeability is not specifically an international roaming problem, uniqueness is. In the past, the US Federal Communications Commission (FCC) handed out the manufacturer codes that allow each manufacturer to generate unique codes independently. However, there is nothing to stop a manufacturer, for phones that are not going to be sold in the US, from using a different system. This could cause international roamers to be denied service because their non-unique ESN is on a fraud list in another country.
The most similar organization to IFAST is the GSM MoU, although the similarity does not run very deep. The IFAST will be much less formal, restricting itself to facilitating voluntary solutions to technical problems. Proponents of IFAST hope that through its informal, cooperative work process, international roaming between AMPS systems will, in a few years, become at least as easy as between GSM systems.
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