LU – Part 4
Sending of the transparent LOC_UPD_ACC message confirms that the MSC/VLR has stored the new Location Area (LAI). This concludes the Location Update process. The control channel that was occupied on the Air-interface has to be released, after the Location Update scenario has ended. For this purpose, the MSC sends the CLR_CMD message to the BSC. The BSC passes this command in a CHAN_REL to the BTS, which passes it to the MS. By sending a DEACT_SACCH, the BSC requests the BTS to cease sending of SACCH messages (SYS_INFO 5/6).The MS reacts on receiving a CHAN_REL message by sending a DISC (LAPDm).
This requests from the BTS to release its Layer 2 connection. The BTS confirms release of the Layer 2 connection by sending an UA message. Towards the BSC, the BTS confirms release of the Air-interface connection by sending of a REL_IND message. The BSC forwards this acknowledgment in a CLR_CMP to the MSC. The BSC requests the TRX in a RF_CHAN_REL to release the occupied resources on the Air-interface. RLSD requests release of the SCCP resources.
RF_CHAN_REL_ACK confirms release on the Air-interface. RLC confirms release of the SCCP resources.