I see cells

hi, tests with layer 3 pointed out a problem. when i select a cell, i get updates of system informations, paging requests and immediate assignments. after about half an hour, i get some corrupt frames. i don't know yet what is wrong. 1. is the communication between the layer 1 and layer 2 (over serial link) secure? 2. i must be sure that a message between layers always are: - never get lost (except unit-data or data when connection is aborted) - never are corrupt - received in the order they are sent 3. does layer 1 drop (bcch) frames, if they have biterrors? (as it should do) andreas