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In this article:
- What is GSM
- History of GSM
- The SIM card
- Security of GSM
What is GSM?
GSM stands for Global System for Mobile Communications. It is a standard for communication between mobile phones all over the world. GSM is the largest used service in the world with more than 2 billion subscribers in 212 countries. This wide coverage allows the various mobile phone operators to provide roaming facilities (ability to use the same mobile phone in different countries without any changes). GSM is a 2nd generation technology and is hence superior to its predecessors. GSM systems provide a very high quality of digital voice over the phone and also allow sending and receiving of short (or long) text messages (called Short Messaging Service or SMS). Since the standard is open and is in continuous development, new features are (such as high speed data transmission etc.) introduced with every new release of the standard. Also, GSM is always kept backward compatible.
History of GSM
The basic problem that the preceding mobile phone standards faced was that of compatibility. To deal with this problem among many others, the GSM group was formed in 1982. A decision had to be made as to which type of system (analog or digital) should be built. The decision was made in favor of a digital system after tests and analysis in 1987. The final system which was chosen in 1987 was made by Torleiv Maseng and Odd Trandem after a competition was held between various proposals. The first GSM specification, however, could not be completed till 1990 and the first commercial implementation and operation started in 1991 with Radiolinja in Finland. In 1998, the 3rd Generation Partnership Project or 3GPP was put in charge of the maintenance and development of the GSM specification. A unique feature of GSM is that it is a set of recommendations, rather than requirements so as to keep the designers free to use any hardware they feel apt.
The SIM card
A typical feature of any GSM service is the SIM card which is short for Subscriber Identity Module. It is type of smart card that is which stores the information about the customer’s subscription and other information such as a phonebook. A SIM card is detachable, making it possible to use it with any mobile phone which is GSM compatible.
Sometimes, handsets may be locked making them incapable of using any other SIM card except the one provided by the operator. These handsets may however be unlocked on the request of the customer in return of a fee. It is also possible for the customer to unlock the handsets themselves by using the information from websites over the Internet which maybe fee-based or free. There exists various rules regarding unlocking handsets in different countries and while it maybe completely legal to do so in one country, it may not be allowed to do so in another.
Security of GSM
GSM is capable of providing moderate security. A subscriber is typically authenticated to the network by making use of a shared-secret cryptography. The data or information that travels between the subscriber or user and the base station can be encrypted to prevent any unauthorized access. Additionally, a longer authentication key maybe used to provide more security. GSM, however, does not authenticate the network to the subscriber and only determines the user as being authentic or not. Thus, there is no possibility of authorization from both sides but confidentiality is still maintained. Apart from this, a good security feature of GSM networks is that the secret key to the cryptographic algorithms of the GSM network which is stored in the SIM card in an encrypted form is never ever sent over the connection. However, the algorithms themselves have been found to be very weak and it is quite easy to break them.
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