IS-136 is an evolution of the IS-54 standard. Both are known as Digital AMPS (D-AMPS), a 2G technology used particularly in the United States and Canada. IS-136 – often also referred to as TDMA – was originally an important mobile radiocommunications standard in the Americas, but it has meanwhile been replaced by GSM/GPRS and CDMA2000 technologies.
D-AMPS transmits in the same 30 kHz frequency bands as analog AMPS, which results in a smooth transition from an analog to a digital system. Voice data is compressed, allowing partitioning into three timeslots. The voice capacity per channel is thus tripled.