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Without its own MIN (Mobile Identification Number), a cellular phone suffers a true identity crisis. This number identifies it uniquely to the network, allowing wireless phones to originate and receive calls with appropriate privileges and features, and ensuring that charges are billed to the right subscriber. The MIN identifier is used in wireless systems in many countries that use AMPS analog systems, IS-54 or IS-136 D-AMPS TDMA digital systems or IS-95 CDMA digital systems. The only major wireless technology that does not use the MIN identifier is GSM. With 10 billion possible different MIN codes, it would seem that there would be enough for everyone. Yet, a shortage looms – not in North America but in all other countries that need this resource.
The shortage of MIN codes is primarily due to an unnecessary restriction that was placed on them in the early days of cellular. Most phones have their MIN programmed with their directory number. In fact, most people probably do not distinguish between these two, assuming that they are simply their “phone number.” However, the distinction between the MIN and the Mobile Directory Number (MDN) is highly significant, although often overlooked today.
The directory number is the number that is dialed when someone wants to call a wireless phone. It is translated into the MIN by the home system, although this translation obviously has no effect when the MIN is the same number. The MIN, on the other hand, is never dialed (with the exception of some roamer port calls) but is used for all communication between the home system and the current serving system, and between this system and the mobile over the radio interface. In most phones, only the MIN is known (even though the manuals may lead one to believe that the directory number is stored) and, in fact, most serving systems are also aware of only the MIN.
It is not quite correct to say that North American directory numbers are used as the MIN – the country code (“1”) is missing. This little omission is a big problem because if every other country programmed their phones in the same way, there would be no way to guarantee uniqueness. Mexico, for example, used to program all their phones starting with the digits “52”, but this came to a screeching halt when the area code “520” was allocated to Arizona.
International wireless carriers have recognized this problem for some time. The solution that they have chosen is to allocate MIN codes that start with the digit 0 or 1, which will eliminate the possibility of conflict with MIN codes based on North American directory numbers. Mexico, for example, is reprogramming all cellular phones from a MIN starting with “52” to a MIN starting with “05”. However, this solution will not guarantee uniqueness between two countries outside North America or with specialized North-American-based systems that already use these non-dialable MINs.
The International Forum on AMPS Standards Technology (IFAST, www.ifast.org ) has taken on the role of allocating what they have named International Roaming MINs (IRMs). This organization acts as a neutral party to allocate the resource in a fair, first-come first-served fashion. However, some companies have already helped themselves to a large portion of this resource, reducing the number of free IRM blocks substantially. The IRM is a 10-digit MIN beginning with the digit 0 or 1, with the first four digits allocated by IFAST to an individual wireless carrier. The remaining 6 digits are allocated by the carrier. This allows for 2,000 distinct blocks of 1 million MINs each. Yet already, after only about a year of allocation by IFAST, almost half the available IRMs have been claimed. With about 100 countries using MIN-based technologies, and with many countries having multiple wireless carriers that each require a separate IRM, the 1,000 remaining blocks may not last long. Add to this the list of satellite carriers, data-over-cellular providers and specialized voice providers who also need the distinct MIN resource that the IRM provides.
The shortage of MINs is not due to wasteful allocation by IFAST; the majority of blocks were allocated by US and Canadian companies before IFAST was created. Without an allocation authority, companies with special purpose systems (mostly data) simply invented ways to use a previously ‘unusable’ resource, and organized the resource in the best way for their company, without considering efficiency or coordination with other companies. The question now is: How long can IFAST continue to hand out IRM codes before the resource is exhausted?
A lack of unique MINs could severely crimp the burgeoning interest in international roaming. Carriers that are denied a unique code will find it difficult or impossible to establish international roaming agreements. A long-term solution to this problem is implementation of the IMSI identifier (International Mobile Station Identity). As the first word suggests, this code was designed with international roaming in mind. However, it will be several years before IMSI is widely implemented in phones, base stations, switches and networks. It is not even available in all standards at present, let alone commercial phones and infrastructure.
Another potential source of MIN codes is North America itself. By constraining the MIN to be a dialable directory number, the majority of MIN codes are implicitly allocated to wireline phone companies (or other telecommunications carriers that do not use the MIN concept, such as paging carriers). Yet these wasted MIN blocks are not available for allocation because of the difficulty of developing and maintaining the huge database that would be necessary to separate the wheat from the chaff. Local Number Portability is going to force the industry to create this database, to support the required separation of MIN and directory number. Consequently, several billion MINs will eventually be freed from servitude. Theoretically, some of these could be used by international carriers, solving the MIN shortage problem. As with IMSI, however, this solution is some time away, and developing the systems and funding necessary to allocate MIN blocks worldwide would be yet another time consuming step.
Vladimir Horowitz said that “the piano is the easiest instrument to play in the beginning and the hardest to master in the end.” The same can be said of numbering. At first the resource seems limitless, and people who want to control it seem like grouchy piano teachers trying to drill an 8 year old who would rather be throwing a ball around outside. But once the resource is close to exhaustion, everyone starts to realize why well-thought-out, conservative planning really was required even in the early days. Except that then it is too late, just like our piano student, now grown up, trying to unlearn bad habits ingrained when he was 8 and just wouldn’t listen.
It is not just MINs that are suffering from exhaustion. Seemingly daily, area code changes reflect the huge demand and inefficient allocation of directory numbers. The 1-800 resource has been exhausted, and the internet is being forced to migrate to a new version of the TCP/IP protocol due to inefficient allocation of address numbers. Wireless carriers may be suffering, but at least they will not be suffering alone.
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