we have the problem at SD level where CCALLA represents the nunnmber of SD attempts and CCONGS the numbr of SD blocks, so CCALLS-CCONGS must equal CMSESTAB which is the number of establishments of SD, but we found out that (CCALLS-CCONGS-CMSESTAB)does nopt equal zero which means that some SD attempts failed but not due to lack of resources, the problem with this behavior is that it is random and without any modifications on the cell level, does any one have any idea about this?
The equation (CCALLS-CCONGS-CMSESTAB) will be zero only if your SD Establishment Rate (not including CNRELCONG) is 100%. Meaning that whenever a MS asks for a SDCCH, it is allocated an SDCCH and the MS also successfully tunes to the SDCCH in the first attempt.
But practically, the MS may be in a low coverage/high interference area where it was unable to LISTEN the SDCCH granted from the BTS so it will resend request for SDCCH (CCALLS). But as the previous granted SDCCH was missed by the MS, (CMESTAB) will not be pegged against that request.