106
ETSI EN 300 392-7 V2.3.1 (2006-06)
In cells of security class 3 the MS may register and authenticate to the new cell and in so doing receive new values of DCK and CCK. When the SwMI supports DCK retrieval during cell re-selection, the MS shall not use U-OTAR PREPARE and may apply AI encryption to location update signalling on the new cell if it possesses a valid CCK for the LA of the new cell. However, if the SwMI does not support DCK retrieval during cell re-selection, and if the MS knows the preferred neighbour cell it should indicate the LA of the new cell using the U-OTAR PREPARE PDU sent on the MCCH and shall start timer T372. When the SwMI receives this signalling it shall forward the DCK belonging to the MS to the cells belonging to the LA (DCK forwarding) if possible. The MS shall reset timer T372 on receipt of D-OTAR NEWCELL. Following this, the MS may apply AI encryption to location update signalling on the new cell if the DCK forwarding was successful and it possesses a valid CCK for the LA of the new cell. If the MS does not know a preferred neighbour cell it cannot indicate the preferred neighbour cell to the SwMI and therefore the SwMI cannot forward the DCK to the new cell. On successful completion of cell re-selection, the MS may only apply AI encryption if the SwMI indicates it supports "DCK retrieval during cell re-selection" (DCK retrieval), shown in table A.104, and the MS possesses a valid CCK for the LA of the new cell.
6.6.2.4
Announced cell re-selection type-3
See also EN 300 392-2 [2], clause 18.3.4.7.4. When the SwMI supports DCK retrieval during cell re-selection, the MS shall not use U-OTAR PREPARE and may apply AI encryption to location update signalling on the new cell if it possesses a valid CCK for the LA of the new cell. However, if the SwMI does not support DCK retrieval during cell re-selection, and if the MS knows the preferred neighbour cell it should indicate the LA of the new cell using the U-OTAR PREPARE PDU and shall start timer T372. When the SwMI receives this signalling it shall forward the DCK belonging to the MS to the cells belonging to the LA (DCK forwarding) if possible. The MS shall reset timer T372 on receipt of D-OTAR NEWCELL. Following this, the MS may apply AI encryption to location update signalling on the new cell if the DCK forwarding was successful and it possesses a valid CCK for the LA of the new cell.
6.6.2.5
Announced cell re-selection type-2
See also EN 300 392-2 [2], clause 18.3.4.7.5. The SwMI shall use the cell identifier in the U-PREPARE to forward the DCK to the new cell (DCK forwarding). On successful completion of cell re-selection, the MS may apply AI encryption on the new cell if it possesses a valid CCK for the location area of the new cell. If the MS does not possess a valid CCK for the new cell it should request it before selection of the new cell.
6.6.2.6
Announced cell re-selection type-1
See also EN 300 392-2 [2], clause 18.3.4.7.6. The SwMI shall use the cell identifier in the U-PREPARE to forward the DCK to the new cell (DCK forwarding). On successful completion of cell re-selection, the MS may apply AI encryption on the new cell if it possesses a valid CCK for the location area of the new cell. If the MS does not possess a valid CCK for the new cell it shall request it before selection of the new cell.
6.6.2.7
Key forwarding
When the SwMI does not support DCK retrieval during cell re-selection, the U-OTAR PREPARE / D-OTAR NEWCELL signalling is used for forwarding the DCK to the new LA and requesting the associated CCK. No other mobility management or call restoration functionality shall be assumed by the SwMI or the MS. Timer T372, Key Forwarding Timer, shall have a value of 5 seconds. T372 shall indicate the maximum time the MM shall wait for a response to U-OTAR PREPARE. If timer T372 expires, or radio link failure occurs, the MS shall abandon signalling and initiate the cell change procedure immediately (see figure 55).
ETSI