We have been using SIM cards in our telephony and some other digital devices such as in smartwatches, for communication with people or some other kind of devices. The SIM card contained some smart electronic components called smart integrated circuit chip in it that when we insert it to device that support the SIM would create a connection to the network operator career. From there, we can use it for whatever SIM could be used for.
Let continue reading to find out more on what SIM card is!
DEFINITION
The acronym SIM stands for Subscriber Identity Module or Subscriber Identification Module. It is an integrated circuit (IC) intended to securely store the International Mobile Subscriber Identity (IMSI) number and its related key, which are used to identify and authenticate subscribers on mobile telephony devices (such as mobile phones, tablets, IoTs, and laptops). Technically, the actual physical card is known as a universal integrated circuit card (UICC). This smart card called SIM is commonly made up of Polyvinyl chloride abbreviated as PVC, with embedded contacts and semiconductors, with the SIM as its primary component. In practise, the term SIM card refers to the entire physical plastic unit and not simply the embedded integrated circuit chip.
SIM cards of various mobile operators.
Image credit: Tim Reckmann from Hamm, Deutschland.
https://commons.wikimedia.org/w/index.php?curid=83154797
REVIEW OF SIM CARD
The Subscriber identity Module (SIM) contains a unique serial number known as integrated circuit card identifier (ICCID), international mobile subscriber identity (IMSI) number, security authentication and ciphering information, temporary information related to the local network, a list of the services the user has access to, and two passwords: a personal identification number (PIN) for ordinary use, and a personal unblocking key (PUK) for PIN unlocking. In Europe, the serial SIM number (SSN) is also sometimes accompanied by an International Article Number (IAN) or the European Article Number (EAN) required when registering online for the subscription of a prepaid card. It is also possible for the user to store contact information on many SIM cards.
SIMs are mostly used on GSM phones, but it can also be used in satellite phones, smart watches, computers, cameras, or IoT devices.
The first SIM cards were in the size of credit and bank cards. Sizes were reduced several times over the years, usually keeping electrical circuit chip contacts the same, so that a larger card could be cut down to a smaller size.
SIMs are transferable among different mobile devices by removing the card itself from one device and inserted to the other device. Though of recent, eSIMs are replacing physical SIM cards in some domains, including cellular telephony. eSIM uses a software-based SIM embedded into an unremovable eUICC.
Multi-SIM devices have two or more SIM card slots for the use of two or more SIM cards, from one or multiple carriers. Multiple SIM devices are commonplace in developing markets such as in Africa, East Asia, South Asia and Southeast Asia, where variable billing rates, network coverage and speed make it desirable for consumers to use multiple SIMs from competing networks. Multi-SIM phones are also useful to separate one's personal phone number from a business phone number, without having to carry multiple devices. Some popular devices, such as the Samsung and iPhone, have multi-SIM variants. However, multi-SIM devices were not common in the US or Europe due to lack of demand. This has changed with mainline products from Apple and Google featuring either two SIM slots or a combination of a physical SIM slot and an eSIM.
BASIC INFORMATION THAT COULD BE STORED ON SIM CARDS
SIM cards store network-specific information used to authenticate and identify subscribers on the network. The most important among these are the integrated circuit card identity (ICCID), international mobile subscriber identity (IMSI), authentication key (Ki), local area identity (LAI) and operator-specific emergency number. The SIM card also stores other carrier-specific data such as the short Message service centre (SMSC) number, service provider name (SPN), service dialling numbers (SDN), advice-of-charge parameters and value-added service (VAS) applications.
SIM cards can come in various data capacities, from 8 KB to at least 256 KB. Any capacity can only be used to store a maximum of 250 contacts on the SIM, but while the 32 KB has room for 33 mobile network codes (MNCs) or network identifiers, the 64 KB version has room for 80 MNCs. This is used by network operators to store data on preferred networks, mostly used when the SIM is not in its home network but is roaming. The network operator that issued the SIM card can use this to have a phone connect to a preferred network that is more economic for the provider instead of having to pay the network operator that the phone discovered first. This does not mean that a phone containing this SIM card can connect to a maximum of only 33 or 80 networks, instead it means that the SIM card issuer can specify only up to that number of preferred networks. If a SIM is outside these preferred networks, it uses the first or best available network.
International mobile subscriber identity (IMSI)
The International Mobile Subscriber Identity (IMSI) is a number that uniquely identifies every user of a cellular network. It is stored as a 64-bit field and is sent by the mobile device to the network. SIM cards are identified on their individual operator networks by this unique IMSI. It is also used for acquiring other details of the mobile in the home location register (HLR) or as locally copied in the visitor location register. To prevent eavesdroppers from identifying and tracking the subscriber on the radio interface, the IMSI is sent as rarely as possible and a randomly-generated Temporary Mobile Subscriber Identity (TMSI) is sent instead. The IMSI is used in any mobile network that interconnects with other networks.
An IMSI is usually presented as a 15-digit number but can be shorter. For example, MTN South Africa's old IMSIs that are still in use in the market are 14 digits long. The format is:
- The first three digits represent the mobile country code (MCC).
- The next two or three digits represent the mobile network code (MNC). Three-digit MNC codes are allowed by E.212 but are mainly used in the United States and Canada. One MCC can have both 2 digit and 3 digit MNCs, an example is 350 007.
- The next digits represent the mobile subscriber identification number (MSIN). Normally there are 10 digits, but can be fewer in the case of a 3-digit MNC or if national regulations indicate that the total length of the IMSI should be less than 15 digits.
- Digits are different from country to country.
Integrated Circuit Card Identifier (ICCID)
Each SIM is internationally identified by its integrated circuit card identifier (ICCID). ICCID is the identifier of the actual physical SIM card itself: i.e. an identifier for the SIM chip. Nowadays ICCID numbers are also used to identify eSIM profiles, and not only physical SIM cards. ICCIDs are stored in the SIM cards and are also engraved or printed on the SIM card body during a process called personalisation. The ICCID is defined by the ITU-T recommendation E.118 as the primary account number. Its layout is based on ISO/IEC 7812. According to E.118, the number can be up to 19 digits long, including a single check digit calculated using the Luhn algorithm. However, the GSM Phase 1 defined the ICCID length as an opaque data field, 10 octets (20 digits) in length, whose structure is specific to a mobile network operator. The digits of an ICCID tend to be a string of numbers that classify a SIM card’s designated industry, country, service provider network and unique ID. After buying and activating a SIM card, the ICCID lets mobile network operators know which network to connect your card and associated device to.
ICCID can sometimes be mistaken for the IMSI. ICCID is the identifier for the physical SIM card itself (or now the virtual SIM card if it is an eSIM). The IMSI lives as part of the profile (or one of several profiles if the SIM and operator support multi-IMSI SIMs) on the SIM/ICCID.
SIM cards showing ICCID
PHYSICAL SIZES AND FORMS OF SIM CARDS
Initially, the physical size for a SIM card was same as the size of bank credit cards. SIM cards have been made smaller over the years due to the rapid changes in Mobile technology as a result of increased on the phone thinness, battery size, and more sophisticated electronic components.
Today, there are several forms of SIM cards:
- Full-size
- Mini or standard
- Micro
- Nano
- Embedded (eSIM)
- Integrated SIM (iSIM)
1 - FULL-SIZE SIM
The full-size SIM also known as 1st form factor (1FF) was the first type of SIM to appeared. It was the size of a credit card (85.60 mm × 53.98 mm × 0.76 mm). As time passed on, smaller SIMs are often supplied but embedded on a full-size card from which they can be removed.
2 - MINI-SIM
The mini-SIM 2nd form factor (2FF) card has the same chip contact arrangement as the full-size SIM card and is normally supplied within a full-size card carrier, attached by a number of linking pieces. The arrangement lets such card be used in a device that requires a full-size card – or in a device that requires a mini-SIM card, after breaking the linking pieces. As the full-size SIM is no longer used, some suppliers refer to the mini-SIM as a standard SIM or regular SIM.
3 - MICRO-SIM
The micro-SIM or 3rd form factor (3FF) card has the same thickness and chip contact arrangements with the previous versions, but with reduced length and width. The micro-SIM was introduced for the purpose of fitting into devices too small for a mini-SIM card.
The form factor was mentioned in the December 1998 3GPP SMG9 UMTS Working Party, which is the standards-setting body for GSM SIM cards, and the form factor was agreed upon in late 2003.
The micro-SIM was designed for backward compatibility. The major issue for backward compatibility was the contact area of the chip. Retaining the same contact area makes the micro-SIM compatible with the prior, larger SIM readers through the use of plastic cutout surrounds. The SIM was also designed to run at the same speed (5MHz) as the prior version.
Micro-SIM cards were introduced by various mobile service providers for the launch of the original iPad, and later for smartphones, from April 2010. The iPhone 4 was the first smartphone to use a micro-SIM card in June 2010, followed by many others.
4 - NANO-SIM
The nano-SIM or 4th form factor (4FF) card was introduced on 11 October 2012, when mobile service providers in various countries started to supply it for phones that supported the format. The nano-SIM measures 12.3 mm × 8.8 mm × 0.67 mm (0.484 in × 0.346 in × 0.026 in) and reduces the format to the contact area while maintaining the existing chip contact arrangements. A small rim of isolating material is left around the contact area to avoid short circuits with the socket. The nano-SIM is 0.67 mm (0.026 in) thick, compared to the 0.76 mm (0.030 in) of its predecessors. 4FF can be put into adapters for use with devices designed for 2FF or 3FF SIMs, and is made thinner for that purpose.
The iPhone 5, which was released in September 2012, were the first device to use a nano-SIM card, followed by other devices.
5 – EMBEDDED SIM (eSIM)
The embedded SIM (eSIM) is the first entirely digital card type. It is a form of programmable SIM and a completely software-based that is embedded directly into a device. The surface mount format provides the same electrical interface as the full size, 2FF and 3FF SIM cards, but is soldered to a circuit board as part of the manufacturing process. In Machine to machine (M2M) applications where there is no requirement to change the SIM card, this avoids the requirement for a connector, improving reliability and security. An eSIM can be provisioned remotely; end-users can add or remove operators without the need to physically swap a SIM from the device.
In September 2017 again, Apple introduced Apple Watch Series 3 featuring eSIM.
6 - INTEGRATED SIM (iSIM)
An integrated SIM (iSIM) is a form of SIM directly integrated into the modem chip or main processor of the device itself. Consequently, they are smaller, cheaper and more reliable than eSIMs, they can improve security and ease the logistics and production of small devices such as in Internet of Things (IoT) applications. In 2021, the German Telekom introduced the nuSIM, an Integrated SIM for IoT devices.
From left, full-size SIM (1FF), mini-SIM (2FF), micro-SIM (3FF), and nano-SIM (4FF)
| SIM Card Format | Introduced | Length | Width | Thickness |
|---|---|---|---|---|
| Full-size (1FF) | 1991 | 85.6mm (3.37in) | 53.98mm (2.125in) | 0.76mm (0.030in) |
| Mini-SIM (2FF) | 1996 | 25mm (0.98in) | 15mm (0.59in) | 0.76mm (0.030in) |
| Micro-SIM (3FF) | 2003 | 15mm (0.59in) | 12mm (0.47in) | 0.76mm (0.030in) |
| Nano-SIM (4FF) | early 2012 | 12.3mm (0.48in) | 8.8mm (0.35in) | 0.67mm (0.026in) |
| Embedded-SIM(eSIM) | 2016 | — | — | — |
All versions of the non-embedded SIM cards shared the same ISO/IEC 7816 pin arrangement.
Some phones need a SIM card to identify the owner and communicate with a mobile network. SIM cards serve an important purpose in telecommunications and mobile technology: They link a physical device with the owner’s account, making it possible to route calls for individuals to the right device and allowing phone companies to accurately measure utilization and charge subscribers for their service.
SIM cards are vital as forensic evidences as it contains location information and a list of all the network towers it has recently connected to. We should always be careful on whom could give physical access to our SIMs, because the call logs in the SIM can be of immense value in the proceedings of an investigation in case of any incidence that may occur.
People should be made aware that SIM cards should not be simply discarded without breaking it into pieces to make it nearly impossible by a stranger or a criminal to steal private data easily, barely by using a SIM card reader.
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