How do SIM cards work?

How do SIM cards work?

Subject : Science and Tech

Section: Awareness in IT

Context:

• In 2021, there were more than 14 billion cellular devices in the world even though there were only seven billion people.

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 by allotting a number known as international mobile subscriber identity (IMSI).
• A SIM card is mandatory to connect to any cellular network that follows the Global System for Mobile Communications (GSM) standard.
• 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. Instead, signals sent by the phone into the network are ‘signed’ by the key, and the network uses the signature to understand whether the phone’s connection is legitimate.
• It is possible to duplicate a SIM card by accessing its key and storing it in multiple cards.
• SIM cards also store information about its own ID number (the integrated circuit card identifier), the IMSI, the subscriber’s location area identity (their current location), a list of preferred networks (to whom the subscriber can connect when roaming), emergency numbers, and – depending on the space available – the subscriber’s contacts and SMS messages.

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. It applies to electronic identification cards, including smart cards.
• In this standard, 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.
• Wires connect the integrated circuit from its bottom side to the metal contacts on the top side, and the contacts interface with the phone’s data connectors.
• The metal contacts have a segmented appearance. Each segment is called a pin and has a specific purpose.
  • For example, pin 1 collects the operating voltage that gives it the power to operate. Pin 3 is to access the SIM’s clock and pin 5 is the grounding. Pin 7 transmits data in and out of the SIM. These pin-wise roles are specified by the ISO/IEC 7816-2 standard; others, numbered 1 through 15, specify various functions of a SIM card and how they are to be implemented, from their “transmission protocols” to “cryptographic information applications”.
• On the network side, the SIM helps a phone establish its place within a cellular network. When a subscriber dials a recipient’s number, the phone sends data via the network – signed by the key on the SIM card – to a telephone exchange. 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.

How have SIM cards changed?

• In 1960s:  West German engineer Helmut Gröttrup first had the idea to stick an integrated circuit in a plastic panel the size of a credit card.
• The European Telecommunications Standards Institute (ETSI) prepared the GSM Technical Specification 11.11 regarding the SIM card.
• After developing the 11.11 standard, ETSI transferred some of its responsibilities to an international consortium of seven organizations called 3GPP (the Telecommunications Standards Development Society in India is one).
• 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.  With 3G networks, ‘SIM’ became only the software; the hardware was called the Universal Integrated Circuit Card (UICC). With 5G, it is being called the Universal SIM (USIM).

What is an eSIM?

• SIM cards shrank from SIM to micro SIM to nano SIM. to the eSIM, with specifications defined by the GSM Association.
• 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 using mobile equipment with this capability don’t have to physically replace their SIM cards when they join or switch networks. Instead, the network operator simply has to reprogram the eSIM, which can also be done remotely.
• An eSIM has two immediate advantages:

1. Environmentally friendlier: its reprogrammability means no need for more plastic and metal for a new SIM.
2. 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 at least two disadvantages:

1. In some countries, including the U.S., eSIMs can be programmed by subscribers themselves.
2. An eSIM can in theory allow network operators to track subscribers’ data, including inside apps on the device, especially in the absence of data privacy laws.

3GPP:

• Established in December 1998.
• The 3rd Generation Partnership Project (3GPP) is an umbrella term for a number of standards organizations which develop protocols for mobile telecommunications. Its best known work is the development and maintenance of:
  • GSM and related 2G and 2.5G standards, including GPRS and EDGE
  • UMTS and related 3G standards, including HSPA and HSPA+
  • LTE and related 4G standards, including LTE Advanced and LTE Advanced Pro
  • 5G NR and related 5G standards, including 5G-Advanced
  • An evolved IP Multimedia Subsystem (IMS) developed in an access independent manner
• 3GPP is a consortium with seven national or regional telecommunication standards organizations (One of them is India) as primary members and a variety of other organizations as associate members.
• The 3GPP organizes its work into three different streams: Radio Access Networks, Services and Systems Aspects, and Core Network and Terminals.

Source : TH