What is the full form of a SIM card?
Sim card is an electronic small chip. GSM mobile devices use a sim card for communication with the mobile operator and the rest of the world. The full form of the sim is the subscriber identity module. As the full form says that it identifies a mobile subscriber globally. It comes with many sizes. At the start of the gsm network, the sim card was in very big size and mobile devices too. Now with the more compact devices, sim size also reduced over time. There nano and macro sim cards. Sim has inbuilt memory and small programs called applets. Sim stores the following:
Text messages. Phone Contacts. Authentication Keys IMSIs and ICCID Applets and other data.
IMSI and SIM :
A sim is nothing without an identity. IMSI assigned by the mobile operator to the sim card. Which is a unique global identifier? Each mobile operator has its own range of IMSIs. Another important thing sim stores are authentication keys. Keys are used for generating authentication vectors at the time of mobile registration and may be on call setup. The communication over the radio channel is encrypted used authentication vectors for security.
ICCID and SIM:
A sim may have multiple IMISs, roaming sim is one of the examples. Based on the roaming location a particular IMSI gets active. ICCID is another unique identifier for the chip, the ICCID number is assigned by a standard body. It is printed on the sim card.
eSIM or embedded sim:
As mobile devices now supporting multiple sim cards. Each operator has its own sim cards, so if you change the mobile service provider. There is a need to change the sim card as well. Each sim may have multiple IMSIs, all should be preconfigured. But this requires to put a very high number of IMSIs in the SIM, at the time of manufacturing. Which is practically impossible as the chip has limited memory. This limits the roaming options for the roaming sim card providers. eSIM is a new option, where a sim card is builtin within the mobile device. Apple is one of the device manufacturers who has launched the phone with eSIM. With eSim any IMSI can be provisioned over the air. This enables the support of a very high number of identities and no change in the chip when changing mobile operators.
SIM and CDMA :
CDMA is another network for mobile communication as similar to GSM. But is less in use. In CDMA there is no sim card, all information is present in the device for network operations. This leads to a serious issue when someone wants to change the device but the phone number.