GSM Call Flow MS Terminated Call Procedure Mobile - Originating Call Procedure INTRA_VLR LOCATION UPDATING OR imsi ATTACH( in old VLR )-GSM Call Flow MS Terminated Call Procedure Mobile- Originating Call Procedure INTRA_VLR LOCATION UPDATING OR IM

a paper about GSM. The cell tower and phone negotiate the highest level of crypto that both mutually support. During call setup a handset sends a packet that states its crypto level and the tower will return a signal with what is actually going to