Thanks for replay AliAsgher, but this is not the case: TA is normal and changes if MS is moving. With UL measurements everything is ok. If MS doesn’t move, than call can go one as long as suscriber wants (we have some calls that are active for half an hour with normal call clearing).
Only thing that is different for these calls are that DL measurements are the same with every report (for example if MS access the cell with -60 dBm level and quality 0, these values stays for all duration of call even of UL drops to -110) and dropped calls happens only to moving MS that drives out of coverage area and there are no HO possible, because BSC thinks that MS have good DL coverage and there are no cells that are good enougth to fulfill DL requements and only in that case radio link failure happens.