GSM -- fixed bit rate, not loss tolerant, narrow band (8khz sampling rate).
iSAC -- variable bit rate, loss tolerant, narrow and wideband (8 to 16khz). Varies based on Bandwidth, packet loss, delay
iLBC -- variable bit rate, loss tolerant, narrow
PCMA -- fixed bit rate (8kHz sampling rate)
PCMU -- fixed bit rate (8kHz sampling rate, high band width)
IPCMWB -- 16 kHz sampling rate
EG711 (enhanced g711) -- fixed bit rate, loss tolerant, narrowband
iPCM -- fixed bit rate, loss tolerant, wide band.