GSM services
GSM services are a standard collection of applications and features available to mobile phone subscribers all over the world. The GSM standards are defined by the 3GPP collaboration and implemented in hardware and software by equipment manufacturers and mobile phone operators. The common standard makes it possible to use the same phones with different companies’ services, or even roam into different countries. GSM is the world’s most dominant mobile phone standard. The design of the service is moderately complex because it must be able to locate a moving phone anywhere in the world, and accommodate the relatively small battery capacity, limited input/output capabilities, and weak radio transmitters on mobile devices. In order to gain access to GSM services, a user needs three things: After subscribers sign up, information about their identity (telephone number) and what services they are allowed to access are stored in a “SIM record” in the Home Location Register (HLR).
