24.008
10.5.5.21 Cell Notification
The purpose of the Cell Notification information element is to indicate that the Cell Notification is supported by the network and shall be then used by MS.
23.060
6.9.1.1 Cell Update Procedure
A cell update takes place when the MS enters a new cell inside the current RA and the MS is in READY state. If the RA has changed, a routeing area update is executed instead of a cell update.
If the network does not support the Cell Notification which is an optimised Cell Update Procedure (see TS 24.008 [13]), the MS performs the cell update procedure by sending an uplink LLC frame of any type except the LLC NULL frame (see TS 44.064 [15]) containing the MS's identity to the SGSN. If the network and the MS support the Cell Notification, then the MS shall use the LLC NULL frame containing the MS's identity in order to perform a cell update. The support of Cell Notification is mandatory for the MS the network, but the network and the MS have to support the Cell Update Procedure without using the LLC NULL frame for backward compatibility reasons.
In the direction towards the SGSN, the BSS shall add the Cell Global Identity including RAC and LAC to all BSSGP frames, see TS 48.018 [78]. A cell update is any correctly received and valid LLC PDU carried inside a BSSGP PDU containing a new identifier of the cell.
The SGSN records this MS's change of cell and further traffic towards the MS is conveyed over the new cell.