A.1 Agreed handover principles

3GPP43.129Packet-switched handover for GERAN A/Gb modeRelease 17Stage 2TS

1. It is the mobile station that is handed over to a target cell when one or more of its PFCs are subject to handover.

2. The source BSS makes the decision to initiate the handover preparation phase when required for PFC(s) subject to handover.

3. Information pertaining to all PDP contexts and PFCs relating to the MS should be sent from the old SGSN to the target SGSN in the handover signalling regardless of their QoS.

4. The target BSS should make the final decision on which PFCs are subject to handover and to assign resources over the Um interface in the target cell. This decision is based on the target BSS being able to fulfil the QoS for these PFCs.

5. The old SGSN decides whether and when to forward data to the TEIDs provided by the new SGSN.

6. It is not required to have resources allocated in advance for bearers which themselves are not determined to be subject to handover by the target BSS.

7. How the target BSS decides which PFCs to accept and which to reject should be implementation specific.

8. For the PS Handover, forwarding of data is performed from the old SGSN either to the target BSS (intra BSS, intra SGSN-inter BSS) or to the new SGSN (inter SGSN); an optional optimisation for intra BSS handover will allow the BSS to decide how to handle the user data flow.

9. An explicit Routing Area Update procedure is performed (if required) when the handover procedure is terminated.

10. The explicit RAU may not contain the following message sequences that are performed already during the handover procedure:

– Transfer of contexts between SGSNs (inter SGSN case).

– Exchange of SNDCP sequence numbers (inter SGSN case).

– Allocation of P-TMSI.

11. Uplink and downlink data transfer continues during the Routing Area Update procedure. This is possible because certain RAU centric functions are performed during the handover execution phase.

12. The PS Handover service shall support intra BSS, intra SGSN-inter BSS, inter SGSN and inter RAT scenarios.

13. Based on the quality of service parameters the MS or the network may throw away packets available for transmission in the uplink or downlink during the ongoing handover procedure.

14. The source BSS shall only request PS handover for one cell in each PS Handover Required message.

15. The PS handover procedure is only performed when the target BSS pre-allocates resource for at least one PFC. In case the target BSS cannot allocate resources for at least one PFC the target BSS shall reject the PS Handover request using the PS Handover Request Negative Acknowledge message.

16. In case the mobile fails to synchronize to the target cell within a timeout period after having received a PS Handover Command, shall revert to the source cell and the old "channels".

17. Optionally, in the case of Intra RAT/Mode PS handover, information pertaining to the radio resource realization of the PFCs subject to Handover can be transferred from the source BSS to the target BSS.

18. During the PS Handover preparation phase the new SGSN (assuming RA change) assigns a unique identifier (P-TMSI, Local TLLI) for data transmission in the target cell. This Local TLLI is used for data transfer between the target BSS and the new SGSN. This Local TLLI is not sent to the MS. After PS Handover Completion the MS triggers the RAU procedure. After P-TMSI reallocation, which is performed during Routing area update, a new Local TLLI will be derived from the P-TMSI using current MM procedures.

19. An SGSN supporting PS handover to GERAN A/Gb mode shall always assign a valid SAPI and PFI upon PDP Context activation for a PS Handover capable MS.

20. An MME supporting PS handover to GERAN A/Gb mode shall always assign a valid SAPI and PFI upon EPS bearer activation for a PS Handover capable MS.

Annex B (informative):
PS Handover Primitives