how mobile sim card works ?

sim (subscriber identity module):

The first SIM card was made in 1991 by Giescke and Deviant of sagem communications in France.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 smart card that can be removed and transferred to different mobile phones.

The data stored in the SIM card includes a unique serial number called ICCID, International Mobile Subscriber Identity or IMSI, Security Authentication information, temporary information about the network, a Personal Identification Number or PIN and a Personal Unblocking code or PUK for unlocking. SIM card contain it’s internally memory in which stores the data, personal and financial information, identity for GSM/CDMA.

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

Keys of SIM Card:

1.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.

2.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.

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.

4. Location Area Identity or LAI– This the information stored in the SIM about the local network available. The operator network is divided into different small areas each having a LAI.

5.Microprocessor-

The most important part of the SIM card is its Micro controller. It is a paper sized chip which is a typical ROM with a size between 64 KB to 512 KB. The RAM size ranged between 1KB to 8KB while the EEPROM size is in between 16KB to 512 KB. The ROM contains the OS or operating system for the card, while the EEPROM contains data called personalization that includes security keys, phone book,  settings etc. The operating voltage of SIM maybe, 1.8V, 3V or 5V but the operating voltages of most of the modern SIM support 5V, 3V and 1.8V.

types :

In the world of mobile phones, there are two primary phone types that are available to consumers: GSM (Global System for Mobile) and CDMA (Code Division Multiple Access). GSM phones are the ones that utilize SIM cards while CDMA phones do not.

The Technology Behind CDMA vs. GSM

CDMA and GSM are both multiple access technologies. They're ways for people to cram multiple phone calls or Internet connections into one radio channel.

GSM came first. It's a "time division" system. Calls take turns. Your voice is transformed into digital data, which is given a channel and a time slot, so three calls on one channel look like this: 123123123123. On the other end, the receiver listens only to the assigned time slot and pieces the call back together.



The pulsing of the time division signal created the notorious "GSM buzz," a buzzing sound whenever you put a GSM phone near a speaker. That's mostly gone now, because 3G GSM (as I explain later) isn't a time division technology.

CDMA required a bit more processing power. It's a "code division" system. Every call's data is encoded with a unique key, then the calls are all transmitted at once; if you have calls 1, 2, and 3 in a channel, the channel would just say 66666666. The receivers each have the unique key to "divide" the combined signal into its individual calls.

Code division turned out to be a more powerful and flexible technology, so "3G GSM" is actually a CDMA technology, called WCDMA (wideband CDMA) or UMTS (Universal Mobile Telephone System). WCDMA requires wider channels than older CDMA systems, as the name implies, but it has more data capacity.

Since its inception, GSM has evolved faster than CDMA. As I mentioned above, WCDMA is considered the 3G version of GSM technology. To further speed things up, the 3GPP (the GSM governing body) released extensions called HSPA, which have sped GSM networks up to as fast as 42Mbps, at least in theory.

 

 

 

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