Rala,
open RNO, go to QOS INDICATORS, in the family SDCCH ASSIGN, subfamily UNSUCCESS CAUSES. You will find it here.
It is an indicator.
The SDNAUR is the correct name :
SDCCH_assign_unsuccess_rate ( SDNAUR )
formula :
( ( [MC04] + ( [MC148 – MC01 – MC02 – MC149] + [MC149])) / [MC04 + MC148])