How SIM Card works? - Extra Know

How SIM Card works?

SIM Card:

SIM4SIM card technology is one of the most popular technology which is used in Mobile phones to activate the connection and to communicate and for making links with the server system and also used in various electrical and electronic projects. It is the Subscriber Identity Module that contains the integrated circuit to store the International Mobile Subscriber Identity or IMSI and the keys to identify and authenticate the subscribers on the communication system. The SIM is embedded in a smart card that can be removed and transferred to different mobile phones. SIM card provides security system to users. The first SIM card was made in 1991 by Giescke and Deviant of Sagem communications in France.

GSM/CDMA. Modern SIM cards allow the storage of application data that communicate with the handset or server using the SIM application tool kit. The SIM card stores network specific information to authenticate the identity of the subscriber in the network. Out of the many keys, the most important keys are ICCID, IMSI, Authentication key or Ki, Local Area Identification or LAI, and an operator specific emergency number. Micro sim have been invented for latest mobile phones. The SIM also contains other data like Short Message Service Centre number or SMSC, Service Provider Name or SPN, Service Dialing Number or SDN, Value Added Service or VAS etc. The SIM comes in various data capacities ranging from 32KB to 128K and can store 250 contacts.

Keys of SIM Card:

1. International Mobile Subscriber Identity or IMSI – It is used to identify the individual operator net work. Normally it has 109 digits. Its first 3 digits represent Mobile Country Code or MCC, the next 2 to 3 digits represents the Mobile Network Code or MNC, The next digits represents the Mobile Subscriber Identification Number or MSIN.

2. Integrated Circuit Card Identifier or ICCID – It is the Primary account number that has 19 digit long. The number has sections like Issuer Identification Number or IIN, Individual Account Identification, Check digit etc.
3. Authentication Key or Ki – It is a 128 bit used to authentication of the SIM card on the Mobile Network. Each SIM has a unique Authentication key assigned by the operator during personalization. The Authentication Key is also stored in the data base of the carrier’s network. When the mobile phone first activates using the SIM card, it gets the International Mobile Subscriber Identity or IMSI from the SIM card and transfers it to the mobile operator for authentication. The data base in the operator system then searches for incoming IMSI and the associated Authentication key. The operator data base then generates a Random Number or RAND and signs it with the IMSI and gives another number called Signed Response 1(SRES_ 1). The RAND will be sending to the mobile phone and the SIM then signs it with the Authentication Key and produces the SRES_ 2 which then passes into the operator network. The operator net work then compares the SRES_1 it produced and the SRES_2 from the mobile phone. If both match, the SIM is authenticated.

Functions of SIM card:

 The SIM card performs the following functions:
 1) It identifies the subscriber: The IMSI programmed on the SIM card, is the identity of a subscriber. Each IMSI is mapped to a mobile number and provisioned on the HLR to allow a subscriber to be identified.
2) Authenticate the subscriber: This is a process, where, using the authentication algorithm on the SIM card, a unique response is provided by each subscriber based on IMSI (stored on SIM) and RAND (provided by network). By matching this response with values computed on the network a legal subscriber is logged on to the network and he or she can now make use the services of the mobile service provider. SIM card is becoming a feature of mobile work.

3) Storage: To store phone numbers and SMS.
4) Applications: The SIM Tool Kit or GSM 11.14 standard allows creating
Applications on the SIM to provide basic information on demand and other
Applications for m-commerce, chatting, cell broadcast, phonebook backup,


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