BSIC -> Base station identity code. this has importance when you cross national boundaries.. well that is the time u have two identical bcch frequencies for a single mobile request.
BSIC is broadcast as part of SCH.
two cells can have identical BSIC in a network but not the neighbouring cells.. Always H PLMN nad adjoining PLMN BSIC’s are different according to the agreement..
Hope it clarifies.