CSD (Circuit-Switched Data)

CSD, or Circuit-Switched Data, was a system used on early GSM networks to provide data access to mobile devices by allowing them to place a data call. CSD was capable of uplink and downlink rates of up to 9.6kbps. Later replaced by the faster HSCSD variant, circuit-switched data on wireless networks were eventually made completely obsolete by packet based networks such as GPRS and EDGE.