It means the MS cannot access the TCH that was allocated by the BTS. Possible problem :
– HW problem :
—TRX BCCH in one sector, TRX TCH on another sector
— poor TX or poor RX of TRX TCH (Path balance)
– SW problem :
— some timeslots cannot be allocated in the TRX (?)
– Radio problems :
— Poor coverage
— High interference on the TCH frequency, whereas the SDCCH frequency is clean
— Too much GPRS traffic –> TS are allocated as PDCH, therefore no more TS for voice. Maybe the PDCH are kept alive for a duration too long after the transfer has been finished.
etc.
Regards,