hi mahmoud,
I would consider taking the msg just before the assg complete ( = assign request ?), which is the last one that’s actually sent on A interface *during* the sd phase.
the assg complete indicates that the MS did land on the TCH successfully.
From the Assign request to the assign complete, the possible problem is a TCH assign failure, which is (usually) due to radio problems on the TCH frequency (which may be different than the SDCCH frequency).
Regards
pix