Digital AMPS (D-AMPS) is a digital system for mobile telephony tha evolved from the analogue AMPS standard. D-AMPS makes use of TDMA to split a analogue 30 kHz radio channel in three digital channels. This made a gradual introduction of digital mobile telephony possible. The original D-AMPS standard was specified in IS-54. IS-54 was later incorporated in the IS-136 (ANSI-136) standard. Because D-AMPS uses TDMA, it is sometimes simply reffered to as TDMA.
ANSI-136 / IS-136 makes use of the old analogue 850 MHz band as well as the 1900 MHz band. IS-136 provides voice and data services with a maximum bit rate of 8 kbit/s and a short messaging service.