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GSM Tele Services

GSM is mainly focused on voice tele services and these comprise of encrypted voice transmission, message services, and basic data communication with terminals as known from the PSTN or ISDN (e.g. fax). However as the main service is telephony, the primary goal of GSM was to provide high-quality digital voice transmission, offering at least the typical audio bandwidth of 3.1 kHz (which was what the old analogue systems offered). Special codecs (coder/decoder) are used for voice transmission. Different codecs are used for the transmission of data for communication with traditional computer modems, e.g. fax machines or the internet.

Another tele service is the emergency number and this is the same number all over the GSM network in Europe and is also the same as the national emergency number. This is a mandatory service that all the network operators have to provide and is free of charge to the user. Another feature is that this service has the highest priority when connecting, possibly pre-empting other connections. Also, the network operators co-operate allowing users of any digital network to use any network to connect and furthermore this service will automatically put the user through to the nearest emergency centre.

A useful additional service that is offered is the short message service (SMS), which is a simple text message transfer service, offering transmission of messages up to about 160 characters. SMS messages do not use the data channels, but instead uses the unused capacity in the signalling channel. The use of the signaling channel means that the user can send and receive SMS messages during a voice or data transmission.

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