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There are fewer people opposed to global roaming than motherhood and apple pie. Yet, technical, business and political realities are making it harder to achieve than the average consumer might expect. The current state of global roaming is reminiscent of someone who has just reached the peak of Mt. Everest. Perhaps the hardest part of the trip is behind them but, if the weather turns, perhaps not.
Advances in wireless technology form a two-edged sword. Without many of them, there would be no phones to roam with, or there might not be any channels available for homers, let alone roamers. But with innovations come incompatibilities. The most obvious incompatibilities, between different radio technologies (AMPS, D-AMPS (US TDMA), GSM, CDMA and several others), are probably the least serious. There are already a number of multi-mode terminals, although nobody has yet attempted to cross the CDMA/TDMA tightrope. Some people joke about 4 pound (2 kilogram) bricks that would result, but if you take the battery, keyboard, outer shell and display off an existing dual-technology, dual-band phone, there is so little left, that it is hard to believe that the size of a triple- or quadruple-mode phone would be a big problem. There are certainly many technical and marketing challenges to multi-mode phones, but where markets demand, manufacturers will surely follow.
More insidious incompatibilities occur in the wireless backbone network, most particularly in mobility applications and SS7 signaling. There are two successful mobility applications for global roaming today: the TIA/EIA-41 standard used by AMPS, NAMPS, D-AMPS and CDMA; and the GSM MAP (which is obviously used by GSM, and which will also be the starting point for the W-CDMA mobility application). The differences are not just because different arrangements of bits and bytes are used to represent the same concept. The very concepts used for short messaging, authentication, feature handling and other capabilities are different. Even within TIA/EIA-41 there are compatibility limitations. It would be very challenging to send a short message to a multi-mode D-AMPS/CDMA phone, due to limitations of the networking protocol, for example. Even locking onto the best local channel would become difficult without more help from the network.
To make matters worse, both mobility applications use SS7 to transport and route messages. Here, the global roaming barriers are not between wireless technologies, but between the many national variants of SS7, of which ANSI SS7, used in the U.S. and Canada, is just the most well-known. Furthermore, SS7 point codes are limited in scope to a single national network, and cannot be used to facilitate international roaming. The alternative, global title translation, requires significant software development, standardization and network upgrades, including international gateway modifications. Imagine if mail to other countries had to be addressed in the language and alphabet of that country. This would require an intermediate stage where companies would transcribe the address from one alphabet (e.g. Chinese) to another. Luckily, post offices long ago standardized on the roman alphabet for international mail. SS7 is like that, where communication within one national network is much easier than between countries. Today, most global roaming is done by extending the ANSI SS7 network to other countries (equivalent to having the U.S. Post Office deliver mail in other countries just because they do not use the roman alphabet).
Wireless technologies that were developed in the U.S. have another hurdle due to their birthplace. The U.S. has such complex internal issues, and such a huge market potential, that it was not necessary to consider international roaming. Their largest trading partner, Canada, even has its telecommunications network integrated with the U.S. GSM, on the other hand, was developed in Europe precisely to replace a forest of older, incompatible national systems with a single pan-European standard. International roaming was built into GSM, but is being bolted on to TIA/EIA-41. Perhaps not surprisingly, GSM is having some technical problems adapting to the U.S. telecommunications environment, which is probably the most complex in the world, while TIA standards are having trouble adapting to international roaming.
One major problem from this heritage is the use of a North American phone number to identify mobile phones. The 10-digit MIN (Mobile Identification Number) does not have to be the same as the phone number, but almost always is (in the U.S. and Canada, at least). Consequently, any MIN beginning with a currently used area code (or a future potential area code) cannot be safely used by international wireless carriers to identify their mobiles roaming in the U.S. The long term solution is to migrate to the 15-digit IMSI (International Mobile Subscription Identity) that is already being used by GSM systems, but unfortunately, it remains a long-term solution, because of the amount of equipment that has to be upgraded to support it.
Probably also because of this heritage, and the enormous size of the U.S. telecommunications marketplace, U.S. carriers have been slow to recognize the potential of international roaming. It is hard to measure when, relatively speaking, it barely exists. And consumers, largely, are unaware of its availability. However, there are a number of organizations that are finally charging forward with this issue. Both the CDG (CDMA Development Group) and the UWC (Universal Wireless Consortium) are encouraging the improvement of international roaming for their favorite technologies. The UWC, which promotes D-AMPS TDMA technology, is even tackling the difficult challenge of inter-working with GSM (which is also TDMA, although beyond that the similarity diminishes rapidly). SS7 network and clearinghouse providers, such as the NACN, BellSouth International and GTE are also busy signing up international customers, although the networking still has limitations (such as the need to allocate ANSI point codes for all international wireless switches). The CTIA was a major force behind the mid-90s effort to resolve Mexican roaming problems, which stimulated the formation of the IFAST (International Forum on AMPS Standards and Technology) in 1996. This organization (www.ifast.org) is trying to resolve both short-term and long-term international roaming issues.
The most immediate need is to ensure that all mobiles have unique Mobile Identification Numbers (MIN codes). Numbers that cannot be confused with those used by North American mobiles (beginning with the digit 0 or 1) are called International Roaming MINs (IRM), and are allocated in blocks of 1 million by the IFAST to needy international, data and satellite operators. Another requirement is that every wireless system have a unique System Identifier (SID). Where the current allocation is insufficient, IFAST has stepped in to allocate a new block to a country, or a satellite carrier.
International roaming is here today, but it is still a bit rough and ready. If I had a wish-list for the future, it would read:
But, please don’t do it tooo quickly, or my consulting career will be threatened!
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