What is a SIM card?
SIM stands for ‘Subscriber Identification Module’.
It is an integrated circuit, or a microchip, that identifies the subscriber on a given network.
Individulas are identified by a number, called the international mobile subscriber identity (IMSI).
The SIM card is a subscriber’s ID card in the city. When someone wants to contact a subscriber in this city, the network uses the subscriber’s SIM card to find them and confirm their identity.
In order for a mobile phone to connect to any cellular network that follows the Global System for Mobile Communications (GSM) standard, a SIM card is mandatory.
What is a SIM card?
This relationship is established using a unique authentication key — a piece of data that a user needs to ‘unlock’ access to the network.
Every SIM card stores this data and it is designed such that the user can’t access it through their phone.
It is possible to duplicate a SIM card by accessing its key and storing it in multiple cards.
How does a SIM card work?
SIM cards are designed according to the ISO/IEC 7816 international standard maintained by the International Organisation for Standardisation and the International Electrotechnical Commission.
The card itself consists of the integrated circuit, which is glued to a silicon substrate on the top side.
On the other side of the substrate are metal contacts, which form the gold-coloured side of the SIM card.
How does a SIM card work?
The metal contacts have a segmented appearance. Each segment is called a pin and has a specific purpose.
On the network side, the SIM helps a phone establish its place within a cellular network.
If the recipient is connected to the same exchange, the network establishes their identity and the call is routed to them.
If the recipient is ‘located’ elsewhere, a computer connected to the network routes the call there according to the most optimum route.
Evolution of SIM cards
The history of smart cards begin in the late 1960s. Helmut Gröttrup first had the idea to stick an integrated circuit in a plastic panel the size of a credit card.
The size and architecture of this microchip evolved in leaps and bounds in the subsequent decades, following Moore’s law.
The SIM card itself evolved according to the standards that defined the networks to which its users wished to connect.
The European Telecommunications Standards Institute (ETSI) prepared the GSM Technical Specification 11.11 regarding the SIM card.
Evolution of SIM cards
GSM concerns the second generation of cellular networks.
After developing the 11.11 standard, ETSI transferred some of its responsibilities to an international consortium of seven organisations called 3GPP .
3GPP subsequently developed the standards for the third (3G), fourth (4G), and fifth generation (5G) of networks.
Until 2G networks, the term ‘SIM card’ denoted both the hardware and the corresponding software.
Evolution of SIM cards
When ‘SIM’ became only the software; the hardware was called the Universal Integrated Circuit Card (UICC).
The software was also upgraded to an application called Universal SIM.
It could be modified to be compatible with the identification and security requirements of 3G, 4G, and 5G networks.
As a result, a UICC loaded with both SIM and USIM applications can work with networks of all generations.
What is an eSIM?
The SIM card has shrunk from the SIM to the mini SIM to the micro SIM to the nano SIM.
In the eSIM paradigm, the SIM software is loaded on to a UICC that is permanently installed in the mobile equipment in the factory itself, that it can’t be removed. (This is called the eUICC.)
Users don’t have to bother with physically replacing their SIM cards when they join or switch networks. The network operator simply has to reprogram the eSIM, which can also be done remotely.
What is an eSIM?
An eSIM has two immediate advantages.
First, it is considered to be environmentally friendlier and its reprogrammability means no need for more plastic and metal for a new SIM.
Second, if a malicious person gains access to your phone, they won’t be able to separately access the SIM application nor be able to duplicate it.
There are also at least two disadvantages.
eSIMs can be programmed by subscribers themselves.
Second, an eSIM can in theory allow network operators to track subscribers’ data, including inside apps on the device.
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