In GSM, there are two types of values presented for RXQUAL, namely RXQUAL FULL and RXQUAL SUB, RXLEV, the parameter representing the signal strength also has similar FULL and SUB values.
The FULL values are based upon all frames on the SACCH multiframe, whether they have been transmitted from the base station or not. This means that if DTX DL has been used the FULL values will be invalid for that period since they include bit error measurements at periods where nothing has been sent resulting in very high BER.
In total, 100 bursts (i.e. 25 blocks) will be used for the FULL values.
The SUB values are based on the mandatory frames on the SACCH multiframe i.e. frames that always must be transmitted. There are two frames fulfilling that criteria and that is SCACCH block and the block holding the SID frame. If DTX DL is not in use, the SID frame will contain an ordinary speech frame and then this is included instead. In total 12 bursts (2 blocks) will be used for the SUB values (4 bursts SACCH and 8 halfbursts SID (or speech) information).