A subscriber identity module or subscriber identification module (SIM) is an integrated circuit that securely stores the international mobile subscriber identity (IMSI) and the related key used to identify and authenticate subscribers on mobile telephony devices (such as mobile phones and computers).
A SIM circuit is embedded into a removable plastic card. This plastic card is called a "SIM card" and can be transferred between different mobile devices. A SIM card follows certain smart card standards. SIM cards were first made the same size as a credit card (85.60 mm × 53.98 mm × 0.76 mm). The development of physically smaller mobile devices prompted the development of smaller SIM cards where the quantity of card surrounding the integrated circuit is reduced.
A SIM card contains its unique serial number (ICCID), international mobile subscriber identity (IMSI), 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 code (PUK) for PIN unlocking.
There are three operating voltages for SIM cards: 5 V, 3 V and 1.8 V (ISO/IEC 7816-3 classes A, B and C, respectively). The operating voltage of the majority of SIM cards launched before 1998 was 5 V. SIM cards produced subsequently are compatible with 3 V and 5 V. Modern cards support 5 V, 3 V and 1.8 V.
The microcontrollers used for SIM cards come in different configurations. The typical ROM size is between 64 KB and 512 KB, typical RAM size is between 1 KB and 8 KB, and typical EEPROM size is between 16 KB and 512 KB. The ROM contains the operating system of the card and might contain applets where the EEPROM contains the so-called personalization, which consists of security keys, phone book , SMS settings, etc., and operating system patches.
Modern SIM cards allow applications to be loaded when the SIM is in use by the subscriber. These applications communicate with the handset or a server using SIM application toolkit , which was initially specified by 3GPP in TS 11.14 (there is an identical ETSI specification with different numbering). ETSI and 3GPP maintain the SIM specifications; the main specifications are: ETSI TS 102 223 , ETSI TS 102 241 , ETSI TS 102 588, and ETSI TS 131 111. SIM toolkit applications were initially written in native code using proprietary APIs. In order to allow interoperability of the applications, Java Card was taken as the solution of choice by ETSI. Additional standards and specifications of interest are maintained by Global Platform.
SIM cards store network-specific information used to authenticate and identify subscribers on the network. The most important of these are the ICCID, IMSI, Authentication Key (Ki), Local Area Identity (LAI) and Operator-Specific Emergency Number. The SIM also stores other carrier-specific data such as the SMSC (Short Message Service Center) number, Service Provider Name (SPN), Service Dialing Numbers (SDN), Advice-Of-Charge parameters and Value Added Service (VAS) applications.
SIM cards can come in various data capacities, from 32 KB to at least 128 KB. All allow a maximum of 250 contacts to be stored 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 information on preferred networks, mostly used when the SIM is not in its home market but is roaming. The network operator that issued the SIM card can use this to have a SIM card connect to a preferred network in order to make use of the best price and/or quality network instead of having to pay the network operator that the SIM card 'saw' first. This does not mean that a SIM card can only connect to a maximum of 33 or 80 networks, but this means that the SIM card issuer can only specify up to that number of preferred networks, if a SIM is outside these preferred networks it will use the first or best available network.
With the GSM Phase 1 specification using 10 octets into which ICCID is stored as packed BCD, the data field has room for 20 digits with hexadecimal digit "F" being used as filler when necessary.
In practice, this means that on GSM SIM cards there are 20-digit (19+1) and 19-digit (18+1) ICCIDs in use, depending upon the issuer. However, a single issuer always uses the same size for its ICCIDs.
To confuse matters more, SIM factories seem to have varying ways of delivering electronic copies of SIM personalization datasets. Some datasets are without the ICCID checksum digit, others are with the digit.
As required by E.118, The ITU regularly publishes a list of all internationally assigned IIN codes in its Operational Bulletins. The most recent list, as of June 2012, is in Operational Bulletin No. 1005
SIM cards are identified on their individual operator networks by a unique International Mobile Subscriber Identity (IMSI). Mobile network operators connect mobile phone calls and communicate with their market SIM cards using their IMSIs. 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.
The next digits represent the Mobile Subscriber Identification Number (MSIN). Normally there will be 10 digits but would 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.
The SIM stores network state information, which is received from the Location Area Identity (LAI). Operator networks are divided into Location Areas, each having a unique LAI number. When the device changes locations, it stores the new LAI to the SIM and sends it back to the operator network with its new location. If the device is power cycled, it will take data off the SIM, and search for the prior LAI.
Full-size SIM
The first to appear was the full-size or 1FF (1st form factor), the size of a credit card (85.60 mm × 53.98 mm × 0.76 mm).
Mini-SIM
The mini-SIM card has the same 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. This arrangement (defined in ISO/IEC 7810 as ID-1/000) allows such a card to be used in a device requiring a full-size card, or in a device requiring a mini-SIM card after breaking the linking pieces.
Micro-SIM
The later 3FF card or micro-SIM cards have the same thickness and contact arrangements, but the length and width are further reduced as above.
The micro-SIM was developed by the European Telecommunications Standards Institute (ETSI) along with SCP, 3GPP (UTRAN/GERAN), 3GPP2 (CDMA2000), ARIB, GSM Association (GSMA SCaG and GSMNA), GlobalPlatform, Liberty Alliance, and the Open Mobile Alliance (OMA) 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 allows the micro-SIM to be 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 (5 MHz) as the prior version. The same size and positions of pins resulted in numerous "How-to" tutorials and YouTube video with detailed instructions how to cut a mini-SIM card to micro -SIM size with a sharp knife or scissors. These tutorials became very popular among first owners of iPad 3G after its release on April 30, 2010, and iPhone 4 on June 24, 2010. The chairman of EP SCP, Dr. Klaus Vedder, said "With this decision, we can see that ETSI has responded to a market need from ETSI customers, but additionally there is a strong desire not to invalidate, overnight, the existing interface, nor reduce the performance of the cards. EP SCP expect to finalise the technical realisation for the third form factor at the next SCP plenary meeting, scheduled for February 2004. 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. Later the Samsung Galaxy S3/S4, various Nokia Lumia handsets and the Nokia N9 followed.
Nano-SIM
On 11 October 2012, mobile service providers began selling the NANOSIM or 4FF (4th form factor) to their mobile users in various countries. The nano sim measures 12.3 × 8.8 × 0.67 mm and reduces the previous format to the contact area while maintaining the existing contact arrangements. A small rim of isolating material is left around the contact area to avoid short circuits with the socket. The 0.7 mm thickness of the NANOSIM is about 15 percent less than its predecessor. 4FF can be put into adapters for use with devices taking 2FF or 3FF SIMs.
Embedded-SIM
SIMs for M2M applications are available in a surface mount SON-8 package which may be soldered directly onto a circuit board.
The surface mount format provides the same electrical interface as the full size, 2FF and 3FF SIM cards, but is soldered to the circuit board as part of the manufacturing process. In M2M applications where there is no requirement to change the SIM card, this avoids the requirement for a connector, improving reliability and security.
When GSM was already in use, the specifications were further developed and enhanced with functionality like SMS, GPRS, etc. These development steps are referred as releases by ETSI. Within these development cycles, the SIM specification was enhanced as well: new voltage classes, formats and files were introduced. In GSM-only times, the SIM consisted of the hardware and the software. With the advent of UMTS this naming was split: the SIM was now an application and hence only software. The hardware part was called UICC. This split was necessary because UMTS introduced a new application, the Universal Subscriber Identity Module (USIM). The USIM brought, among other things, security improvements like the mutual authentication and longer encryption keys and an improved address book.
"SIM cards" in developed countries are today usually UICCs containing at least a SIM and a USIM application. This configuration is necessary because older GSM only handsets are solely compatible with the SIM and some UMTS security enhancements do rely on the USIM.
The equivalent of SIM on CDMA networks is the R-UIM (and the equivalent of USIM is CSIM).
A virtual SIM is a mobile phone number provided by a mobile network operator that does not require a SIM card to connect phone calls to a user's mobile phone.
Abbreviations related to Network
SIM - Subscriber Identification Module
USIM - Universal Subscriber Identity Module
GSM - Global System for Mobile Communications
IMSI - International Mobile Subscriber Identity
ICCID - Integrated Circuit Card Identifier
IIN - Issuer Identification Number
DES - Data Encryption Standard
AES - Advanced Encryption Standard
GPS - Global Positioning System
CDMA - Code-Division Multiple Access
WCDMA - Wideband Code Division Multiple Access
TD-SCDMA - Time Division-Synchronous Code Division Multiple Access
UMTS - Universal Mobile Telecommunications System
PIN - Personal Identification Number
PUK - Personal Unblocking Code
2G - 2nd Generation
3G - 3rd Generation
EDGE - Enhanced Data for Global Evolution
GPRS - General Packet Radio Service
DC-HSDPA - Dual Carrier or Dual Cell High-Speed Downlink Packet Access
HSDPA - High-Speed Downlink Packet Access
HSDPA+ - High-Speed Downlink Packet Access Plus
HSUPA - High-Speed Uplink Packet Access
EDR - Enhanced Data Rate
EGSM - Extended GSM
iDEN - Integrated Digital Enhanced Network
MMS - Multimedia Messaging Service
MNC - Mobile Network Codes
MSIN - Mobile Subscriber Identification Number
A-GPS - Assisted GPS
APN - Access Point Name
MHz - Megahertz
KHz - Kilohertz
Mbps - Megabit per second
Kbps - Kilobits per second
KB - Kilobyte
Gbps - Gigabits per second
CMOS - Complementary metal-oxidesemiconductor
LAI - Local Area Identity
SMSC - Short Message Service Center
SPN - Service Provider Name
SDN - Service Dialing Numbers
VAS - Value Added Service
IMAP - Internet Message Access Protocol
IP - Internet Protocol
EMS - Enhanced Message Service
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