A.3 Mobility procedure

25.4673GPPRelease 17Stage 2TSUTRAN architecture for 3G Home Node B (HNB)

Figure A.3-1: Inter-HNB Inter-HNB-GW SRNS Relocation – Implementation of CN functions for SRNS Relocation within the HNB-GW.

1. The UE has established an active CS/PS session to the CN via the source HNB and HNB-GW.

2. At some point, the source HNB makes a decision to relocate the UE session.

3. The source HNB triggers relocation of the UE session by sending the RANAP Relocation Required message encapsulated in the RUA Direct Transfer message to the HNB-GW. The target RNC-Id and target Cell-Identity information along with relocation information are included by the source HNB in the RANAP Relocation Required message.

4. The HNB-GW constructs the RANAP RELOCATION REQUEST using the stored RAB Parameters and parameters received from source HNB. The RANAP message also includes the HNB-GW UL TNL information for each RAB to be setup at the target HNB.

5. Steps for HNB-GW Triggered UE Registration are executed between the HNB-GW and the HNB. The IuhUPIF function handles the CS user plane establishment in the HNB-GW. The RANAP message from the target HNB includes the target HNB DL TNL information for each RAB to be setup. In case the target HNB decides to use the alternative RAB parameters and indicates the same in the RANAP RELOCATION ACKNOWLEDGE message, the HNB-GW rejects the relocation towards the target HNB and redirects original relocation request towards the CN node as in subclause 5.9.
In this phase, HNB-GW may begin bi-casting DL traffic to the source and target HNB.

6. The HNB-GW constructs the appropriate RANAP Relocation Command message and routes the RANAP message encapsulated in the RUA Direct Transfer message to the source HNB.

7-11. The rest of the relocation procedure continues as shown in the corresponding steps in the above figure. When the relocation is detected in HNB-GW, the HNB-GW switches the user plane from the source HNB to the target HNB.

12. The HNB-GW upon getting an indication that the UE has been successfully relocated to the target HNB triggers the Iu release procedure towards the source HNB by sending a RUA encapsulated RANAP Iu Release Command message.

13. The source HNB acknowledges the Iu release procedure to the HNB-GW by sending a RUA encapsulated RANAP Iu Release Complete message.

NOTE: Steps 2 to 13, as appropriate, are repeated for the second CN domain when present with the following exception. There is only one Context Id allocated to the UE regardless of the number of signalling domains relocated.

14. The HNB-GW deregisters the UE from the source HNB. The source HNB releases the resources assigned to the UE and deletes all stored context information associated with the UE.