GSM is the most successful digital mobile telecommunication system in the world today. It is used in more than 190 countries. GSM permits the integration of different voice and data services and the inter working with existing networks. Services make a network interesting for customers. GSM has defined three different categories of services:
- Telephony (also referred as tele-services) Services
- Data (also referred as bearer services) Services
- Supplementary Services
1. Tele-Services or Telephony Services :
GSM mainly focuses on voice-oriented Teleservices. These comprise encrypted voice transmission, message services, and basic data communication with terminals as known from the PSTN or ISDN
- Voice Calls: The most basic Tele-Services supported by GSM is telephony. This includes full rate speech at 13 Kbps and emergency calls, where the nearest emergency service provider is notified by dialing three digits.
- VideoText and Facsimile: Another group of Tele-Services includes Videotext access, Teletext transmission, and Facsimile alternate speech and facsimile Group 3, automatic facsimile Group 3 etc.
- Short Text Messages: SMS service is a text messaging which allow you to send and receive text messages on your GSM mobile phones.
- Multimedia Message Services:
- Location Based Services:
2. Data Services or Bearer Services
Using your GSM phone to receive and send data is the essential building block leading to widespread mobile Internet access and mobile and mobile data transfer. GSM currently has a data transfer rate of 9.6k. New development that will push up data transfer rated for GSM users HSCSD are now available.
3. Supplementary Services
Supplementary services are provided on top of TeleServices or bearer services, and include features such as caller identification, call forwarding, call waiting, multi-party conversation. A brief description of supplementary services is given here:
- Multiparty Service or conferencing: The multiparty service allows a mobile subscriber to establish multiparty conversations. That is, conservation between three or more subscribers to setup a conference calls. This service is only applicable to normal telephony.
- Call Waiting: This service allows a mobile subscriber to be notified of an incoming call during a conversation. The subscriber can answer, reject or ignore the incoming call. Call waiting is applicable to all GSM telecommunications services using circuit switched connection.
- Call Hold: This service allows a mobile subscriber to put an incoming call on hold and then resume this call. The call hold service is only applicable to normal telephony.
- Call Forwarding: The call forwarding supplementary service is used to divert calls from the original recipient to another number, and is normally set up by the subscriber himself. It can be used by the subscriber to divert calls from the Mobile Station when the subscriber is not available, and so to ensure that calls are not lost. A typical scenario would be a salesperson turns off his mobile phone during a meeting with customer, but does not wish to lose potential sales leads while he is unavailable.
- Call Barring: The concept of barring certain type of calls might seem to be a supplementary disservice rather than service. However, there are times when the subscriber is not the actual user of the Mobile Station, and as a consequence may wish to limit its functionality, so as to limit charges incurred. If the subscriber and users and one and same, the call barring may be useful to stop calls being routed to international destinations when they are route. The reasons for this are because it is expected that are roaming subscriber will pay the charges incurred for international re-routing of calls. So, GSM devised some flexible services that enable the subscriber to conditionally bar calls.