High Speed Circuit Switched Data (HSCSD)

A dedicated circuit-switched data communications technology for GSM networks that enables data speeds to be boosted from 9.6kbps up to 57.6kbps, by combining timeslots.

HSCSD uses up to four 9.6Kb (on 900 Mhz GSM networks) or 14.4Kb (on 1800 MHz GSM networks) time slots, for a total bandwidth of 38.4Kb or 57.6Kb. An asymmetrical service can be offered where, for instance, one channel is allocated for the uplink and several are aggregated for the downlink. HSCSD can provide a fixed bit rate (transparent mode) or a variable one (non-transparent mode).

HSCSD started to appear in some networks in 1999. The Orange network supports this service in the UK. HSCSD is relatively expensive in most GSM networks and so packet-switched GPRS, in which charges are based on amount of data transferred, has become more popular than HSCSD, in which the user is charged by the number of time-slot provided for the total period of time for which the user has connection active.

HDD      High-Speed Downlink Packet Access (HSDPA)