Are you talking about the Call Setup or the Handover phase..
Normally ROC is pegged when the destination TS cannot be successfully camped on and reverts. In Call setup if its assigned to inner zone and a feature like second assignment is there then too its pegged check the assignment / handover command for the TRX to which the call is assigned at. Its HW can be faulty / check its frequency, if SFN check MAL /MAIO if fixed frequency check the C/I plot of the frequencies to identify the problematic frequency. or disable hopping (and swap frequencies assigned to TRX) to check which frequency / HW is generating the Reversions