7.6 Handover procedure

23.3163GPPRelease 18TSWireless and wireline convergence access support for the 5G System (5GS)

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

7.6.1 General

This clause includes the differences for 5G-RG comparing to TS 23.502 [3] clause 4.9.

Handover procedures in this clause are not supported for FN-RG. SRVCC is not applicable to RG.

7.6.2 Handover within NG-RAN

If the 5G-RG is connected via FWA, the procedures in TS 23.502 [3] clause 4.9.1 apply with the differences shown as below:

– UE is replaced by 5G-RG.

7.6.3 Handover procedures between 3GPP access / 5GC and W-5GAN access

7.6.3.1 Handover of a PDU Session procedure from W-5GAN access to 3GPP access

This clause specifies how to hand over a 5G-RG from a source W-5GAN access to a target 3GPP access and how a 5G-RG can handover a PDU Session from W-5GAN access to 3GPP access. It is based on the PDU Session Establishment procedure for 3GPP access as specified in clause 4.3.2 of TS 23.502 [3].

Figure 7.6.3.1-1: Handover of a PDU Session procedure from W-5GAN access to 3GPP access

The Handover of a PDU Session procedure specified in TS 23.502 [3] clause 4.9.2.1 applies with the following changes.

1-2. These steps are the same as steps 1-2 in TS 23.502 [3] clause 4.9.2.1 with the difference that the UE is replaced by 5G-RG.

3. The SMF executes the release of resources in W-5GAN access by performing steps 4 to 6 specified in clause 7.3.3, followed by step 7a specified in clause 4.3.4.2 of TS 23.502 [3] in order to release the resources over the source W-5GAN access. Because the PDU Session shall not be released, the SMF shall not send the NAS PDU Session Release Command to the 5G-RG. Hence, in steps 4 and 6 of clause 7.3.3 as well as in step 7a in clause 4.3.4.2 of TS 23.502 [3], the messages do not include the N1 SM container but only the N2 PDU Session Resource Release Command (resp. Response). Since the PDU Session is not to be released, the SMF shall not execute step 7b in clause 4.3.4.2 of TS 23.502 [3] and the SM context between the AMF and the SMF is maintained.

Steps 2 and 3 shall be repeated for all PDU Sessions to be moved from to W-5GAN access to 3GPP access.

7.6.3.2 Handover of a PDU Session procedure from 3GPP to W-5GAN access

This clause specifies how to hand over a 5G-RG from a source 3GPP access to a target W-5GAN access and how a 5G-RG can handover a PDU Session from 3GPP access to W-5GAN access. It is based on the PDU Session Establishment procedure for W-5GAN access as specified in clause 7.3.1.

Figure 7.6.3.2-1: Handover of a PDU Session from 3GPP access to W-5GAN access

The Handover of a PDU Session procedure specified in TS 23.502 [3] clause 4.9.2.2 applies with the following changes.

1. If the 5G-RG is not registered via W-5GAN access, the 5G-RG shall initiate Registration procedure as defined in clause 7.2.1.1.

2. The 5G-RG performs PDU Session Establishment procedure in W-5GAN access with the PDU Session ID of the PDU Session to be moved as specified in clause 7.3.1.

3 This step is the same as step 3 in TS 23.502 [3] clause 4.9.2.2 with the difference that the UE is replaced by 5G-RG. If the User Plane of the PDU Session is already deactivated in 3GPP access, this step is skipped.

Steps 2 and 3 shall be repeated for all PDU Sessions to be moved from 3GPP access to W-5GAN access.

7.6.4 Handover procedures between 3GPPaccess / EPS and W-5GAN/5GC access

7.6.4.1 Handover from 3GPP access / EPS to W-5GAN / 5GC

Figure 7.6.4.1-1: Handover from EPS to W-5GAN/5GC

The procedure specified in clause 4.11.3.1 of TS 23.502 [3] (Handover from EPS to 5GC-N3IWF) applies with the following changes.

0. Initial status: one or more PDN connections have been established in EPC between the 5G-RG and the PGW-C+SMF via E-UTRAN.

1. The 5G-RG initiates Registration procedure via W-5GAN access according to clause 7.2.1.1.

2. The 5G-RG initiates a PDU Session Establishment with Existing PDU Session indication in 5GC via W-5GAN access according to clause 7.3.1.

3. This step is the same as step 3 in clause 4.11.3.1 of TS 23.502 [3].

7.6.4.2 Handover from W-5GAN / 5GC access to 3GPP-access / EPS

Figure 7.6.4.2-1: Handover from W-5GAN/5GC to EPS

0. Initial status: one or more PDU Sessions have been established via W-5GAN / 5GC access. During PDU Session setup, and in addition to what is specified in clause 4.3.2.2.1 of TS 23.502 [3], the PGW-C+SMF sends the FQDN related to the S5/S8 interface to the HSS+UDM which stores it.

1. If the UE is not attached to EPC/E-UTRAN, the UE initiates Handover Attach procedure in E-UTRAN as described in TS 23.401 [24] for a non-3GPP to EPS handover with "Handover" indication, except note 17.

If the UE is attached in EPC/E-UTRAN, the UE initiates the PDN Connection establishment with "Handover" indication procedure as described in TS 23.401 [24].

2. The combined PGW-C+SMF initiates a network requested PDU Session Release via W-5GAN access according to clause 7.3.3, steps 4-7 to release the 5GC and W-5GAN resources with the following exception:

– Nsmf_PDUSession_SMContexStatusNotify service operation invoked by the SMF indicates the PDU Session is moved to another system.

– The Npcf_SMPolicyControl_Delete service operation to PCF shall not be performed.