11.213GPPBase Station System (BSS) equipment specificationRadio aspectsRelease 1999TS
1) Frame Erasure Ratio (FER):
The frame is defined as erased if the error detection functions in accordance with GSM 05.03 (ETS 300 909)  indicate an error. For full‑rate speech this is the result of a 3 bit Cyclic Redundancy Check (CRC), for signalling the result of the FIRE code or other block code used. For data traffic the FER is not defined.
NOTE: For full‑rate speech it would ideally be better if the Bad Frame Indication (BFI) is used as frame erasure indication since this is what is directly related to the subjective quality of the perceived speech. For the moment no requirements relate to the BFI, however, it is very difficult to assess what is subjectively the optimum combination of Frame Erasure Ratio (FER) and Residual Bit Error Ratio (RBER). This should therefore be avoided and it is essential that the BFI is optimized towards the ideal frame erasures independent of the processing to obtain it, and that the BFI is not biased towards BFI=0 or BFI=1.
2) Residual Bit Error Ratio (RBER):
The RBER is defined as the residual Bit Error Ratio (BER) in frames which have not been declared as erased.
3) Bit Error Ratio (BER):
The BER is the overall Bit Error Ratio (BER) independent of frame erasures or when erased frames are not defined.
Annex B (informative):
Description of special test equipment