MSC-A MSC-B MSC-B' E Prepare Subsequent Handover Request (AN-APDU: Handover Required) E Prepare Handover Request (AN-APDU: Handover Request) E Prepare Handover Response (AN-APDU: Handover Request Ack) E Prepare Subsequent Handover Response (AN-APDU: Handover Request Ack) E Process Access Signalling Request (AN-APDU: Handover Detect) E Process Access Signalling Request (AN-APDU: Handover Complete) E Close