Should we call SIM cards SIM cards?
In my role as a technical trainer I get to meet lots of telecom engineers from a great number of companies, and have noticed a very widespread misuse of certain terms – like, for example, using “LTE” for the E-UTRAN/EPS 4/4.5G systems… One of the most common industry-wide cases is using the term “SIM card” to refer to that small, almost-rectangle shaped hardware card that is inserted into mobile devices to hold subscription related data.
SIM cards – yes, they were the very first in the line. Back in 1991. The original hardware, identified with a unique hardware number, the ICCID, carried software and data that contained the information necessary for a GSM phone to be able to access and correctly use the GSM network. The SIM cards stored the IMSI, International Mobile Subscriber Identity, to link these parameters to a particular subscription within one mobile network operator’s domain. As the GSM system went live it became clear that there is a big number of areas where the service could benefit from various improvements. Probably the most clear need that has emerged was to strengthen the system’s security mechanisms. It seemed natural to bring all the improvements on board as the UMTS system was being designed, but the new solutions required new parameters, which could not be held in the original Elementary Files defined for SIM cards.
Of course, this problem could easily be solved by defining a new, UMTS-specific card dedicated for use with 3G-enabled phones. That approach, however, would make it impossible for the subscriber to move various cards between different models of phones, which was not really seen as acceptable. The decision instead was to divide the original subscription card into hardware (that would be the actual physical platform, in the shape of the original card) and software. The UICC, Universal Integrated Circuit Card, was therefore defined to become the new hardware platform, with the SIM application software providing the 2/2.5G parameters to older phones, and the USIM application with 3/3.5G parameters for the newer phones.
The UICC cards still use the original hardware identifier, the ICCID, and can nowadays, apart from the SIM and USIM applications, also carry an ISIM – IMS Subscriber Identity Module, for IMS-specific information, or other, operator-specific applications. And all of the 3GPP-defined applications – U/I/SIM – are, just as the original SIM cards, uniquely linked to one particular IMSI, holding therefore a certain operator’s parameters in the subscriber’s phone. If you would like to learn about cards that can hold multiple operator’s subscriptions, have a look into an article on eUICCs here: Do we need a new type of SIM card?
We should not really talk about SIM cards nowadays. It’s either a UICC card, if we are speaking about the hardware, or a U/I/SIM application (or module), should we want to refer to the database holding the actual parameters…
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