Originally, Enhanced Data rates for Global Evolution.A 2.5G standard (1999) developed by the European Telecommunications Standards Institute (ETSI) as the final stage in the evolution of data communications within the Global System for Mobile Communications (GSM) standards. The only IMT-2000 specification based on time division multiple access (TDMA) rather than code division multiple access (CDMA), EDGE supports data transmission rates up to 473.6 kbps over GSM channels 200 kHz wide through an improved modulation technique known as 8-Phase Shift Keying (8-PSK), which involves eight levels of phase shift and, therefore, supports three bits per symbol. EDGE employs frequency division duplex (FDD) to support bidirectional communications over 124 channels, each of which supports 8 time slots. EDGE supports two modes of operation: