I am using Siemens. Phantom RACH is one of the reasons for SDCCH congestion. When BSC gives immediate Assignment message for SDCCH via RACH, BSC runs T3101. If timer the dedicated channel is not
established before T3101 expires, the allocated channel is released.
This scenario can e.g. occur if noise on the radio is decoded as
RACH access (“phantom RACH”) by mistake.
If this is a case, setting a long time for it means long time to wait for SDCCH response from MS which does not exist. This gives lower Traffic but SDCCH congestion.
If this a case, I hope decreasing it will solve the problem.