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full Contents for  TS 23.502  Word version:   16.4.0

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1…   4.2.2.2.2   4.2.2.2.3…   4.2.3…   4.2.3.3   4.2.4…   4.2.6   4.2.7…   4.2.9…   4.3…   4.3.2.2…   4.3.2.2.2   4.3.2.2.3…   4.3.3   4.3.4   4.3.5…   4.3.5.2…   4.3.5.4…   4.3.5.6…   4.3.6…   4.4…   4.5…   4.9…   4.9.1.3…   4.9.2…   4.11…   4.11.1.2.2…   4.11.1.3…   4.11.1.4…   4.11.1.5…   4.11.2   4.11.3…   4.12…   4.12.6…   4.12a   4.12b   4.13…   4.13.4…   4.13.6…   4.14…   4.15…   4.15.4…   4.16…   4.16.4…   4.16.8…   4.17…   4.17.9…   4.18…   4.19…   4.23…   4.23.7…   4.23.9…   4.23.11…   4.24   4.25   4.26…   5…   5.2.3…   5.2.5…   5.2.6…   5.2.7…   5.2.8…   5.2.9…   5.2.12…   A…   E…   F…

 

4.13.6  Support of IMS Voice
4.13.6.1  EPS fallback for IMS voice
Figure 4.13.6.1-1 describes the EPS fallback procedure for IMS voice.
When the UE is served by the 5G System, the UE has one or more ongoing PDU Sessions each including one or more QoS Flows. The serving PLMN AMF has sent an indication towards the UE during the Registration procedure that IMS voice over PS session is supported, see clause 5.16.3.10 in TS 23.501 and the UE has registered in the IMS. If N26 is not supported, the serving PLMN AMF sends an indication towards the UE during the Registration procedure that interworking without N26 is supported, see clause 5.17.2.3.1 in TS 23.501.
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Step 1.
UE camps on NG-RAN in the 5GS and an MO or MT IMS voice session establishment has been initiated.
Step 2.
Network initiated PDU Session modification to setup QoS flow for voice reaches the NG-RAN (see N2 PDU Session Request in clause 4.3.3).
Step 3.
NG-RAN is configured to support EPS fallback for IMS voice and decides to trigger fallback to EPS, taking into account UE capabilities, indication from AMF that "Redirection for EPS fallback for voice is possible" (received as part of initial context setup as defined in TS 38.413), network configuration (e.g. N26 availability configuration) and radio conditions. If NG-RAN decides not to trigger fallback to EPS, then the procedure stops here and following steps are not executed.
NG-RAN may initiate measurement report solicitation from the UE including E-UTRAN as target.
NOTE 1:
If AMF has indicated that "Redirection for EPS fallback for voice is not possible", then AN Release via inter-system redirection to EPS is not performed in step 5.
Step 4.
NG-RAN responds indicating rejection of the PDU Session modification to setup QoS flow for IMS voice received in step 2 by PDU Session Modification Response message towards the PGW-C+SMF (or H-SMF+P-GW-C via V-SMF, in the case of home routed roaming scenario) via AMF with an indication that mobility due to fallback for IMS voice is ongoing. The PGW-C+SMF maintains the PCC rule(s) associated with the QoS Flow(s) and reports the EPS Fallback event to the PCF if PCF has subscribed to this event.
Step 5.
NG-RAN initiates either handover (see clause 4.11.1.2.1), or AN Release via inter-system redirection to EPS (see clause 4.2.6 and clause 4.11.1.3.2), taking into account UE capabilities. The PGW-C+SMF reports change of the RAT type if subscribed by PCF as specified in clause 4.11.1.2.1, or clause 4.11.1.3.2.6. When the UE is connected to EPS, either 6a or 6b is executed
Step 6a.
In the case of 5GS to EPS handover, see clause 4.11.1.2.1, and in the case of inter-system redirection to EPS with N26 interface, see clause 4.11.1.3.2. In either case the UE initiates TAU procedure; or
Step 6b.
In the case of inter-system redirection to EPS without N26 interface, see clause 4.11.2.2. If the UE supports Request Type flag "handover" for PDN connectivity request during the attach procedure as described in clause 5.3.2.1 of TS 23.401 and has received the indication that interworking without N26 is supported, then the UE initiates Attach with PDN connectivity request with request type "handover".
In inter-system redirection, the UE uses the emergency indication in the RRC message as specified in clause 6.2.2 of TS 36.331 and E-UTRAN provides the emergency indication to MME during Tracking Area Update or Attach procedure. For the handover procedure see clause 4.11.1.2.1, step 1.
Step 7.
After completion of the mobility procedure to EPS or as part of the 5GS to EPS handover procedure (see clause 4.11.1.2.1), the SMF/PGW re-initiates the setup of the dedicated bearer(s) for the maintained PCC rule(s) in step 4 including of the dedicated bearer for IMS voice, mapping the 5G QoS to EPC QoS parameters. The PGW-C+SMF behaves as specified in clause 4.9.1.3.1. The PGW-C+SMF reports about Successful Resource Allocation and Access Network Information if subscribed by PCF.
The IMS signalling related to IMS voice call establishment continues after step 1 as specified in the TS 23.228.
At least for the duration of the voice call in EPS the E-UTRAN is configured to not trigger any handover to 5GS.
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4.13.6.2  Inter RAT Fallback in 5GC for IMS voiceWord-p. 279
Figure 4.13.6.2-1 describes the RAT fallback procedure in 5GC for IMS voice.
When the UE is served by the 5GC, the UE has one or more ongoing PDU Sessions each including one or more QoS Flows. The serving PLMN AMF has sent an indication towards the UE during the Registration procedure that IMS voice over PS session is supported, see clause 5.16.3.10 in TS 23.501 and the UE has registered in the IMS.
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Step 1.
UE camps on source NG-RAN in the 5GS and an MO or MT IMS voice session establishment has been initiated.
Step 2.
Network initiated PDU Session modification to setup QoS flow for IMS voice reaches the source NG-RAN (see N2 PDU Session Request in clause 4.3.3).
Step 3.
If source NG-RAN is configured to support RAT fallback for IMS voice, source NG-RAN decides to trigger RAT fallback, taking into account on UE capabilities, network configuration and radio conditions.
Source NG-RAN may initiate measurement report solicitation from the UE including target NG-RAN.
Step 4.
Source NG-RAN responds indicating rejection of the PDU Session modification to setup QoS flow for IMS voice received in step 2 by PDU Session Response message towards the SMF (or V-SMF, in the case of roaming scenario) via AMF with an indication that mobility due to fallback for IMS voice is ongoing. The SMF maintains the PCC rule(s) associated with the QoS Flow(s).
Step 5.
Source NG-RAN initiates Xn based Inter NG-RAN handover (see clause 4.9.1.2) or N2 based inter NG-RAN handover (see clause 4.9.1.3), or redirection to E-UTRA connected to 5GC (see clause 4.2.6). The SMF reports change of the RAT type if subscribed by PCF.
Step 6.
After completion of the Inter NG-RAN (inter-RAT) handover or redirection to E-UTRA connected to 5GC, the SMF re-initiates the PDU Session modification to setup QoS flow for IMS voice. The SMF reports about Successful Resource Allocation and Access Network Information if subscribed by PCF.
The IMS signalling related to IMS voice call establishment continues after step 1 as specified in TS 23.228.
At least for the duration of the IMS voice call the target NG-RAN is configured to not trigger inter NG-RAN handover back to source NG-RAN.
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4.13.6.3  Transfer of PDU session used for IMS voice from non-3GPP access to 5GS [R16]Word-p. 280
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When the UE has an ongoing IMS voice session via non-3GPP access using ePDG or N3IWF, and the session is transferred to NG-RAN, depending on the selected RAT in 5GS (NR or E-UTRA), and the support of EPS/inter-RAT fallback in NG-RAN, either the IMS voice session continues over NG-RAN (E-UTRA) or EPS/inter-RAT fallback is triggered.
Steps 1, 2 and 3 apply to either of the above two cases.
Step 1.
UE has ongoing IMS voice session via non-3GPP access using ePDG or N3IWF. UE is triggered to move to 3GPP access and camps in NG-RAN.
Step 2.
If the UE is not registered via 3GPP access, the UE shall initiate Registration procedure as defined in clause 4.2.2.2.2.
Step 3.
UE initiates PDU session establishment for the PDU session used for IMS voice service in order to initiate handover from EPC/ePDG to 5GS as defined in clause 4.11.4.1 step 2 or to initiate handover from N3IWF to 3GPP access in 5GC in step 2 of clauses 4.9.2.1 and 4.9.2.3. The SMF accepts the successful PDU session transfer to the UE in NAS.
NOTE 1:
If the UE is aware (e.g implementation-dependent mechanisms) that voice over NR may not be natively supported in the current Registration area, the UE can attempt to move to E-UTRA to initiate a handover of the IMS PDU Session to EPC or 5GC to continue the IMS voice session. The remaining steps are not executed.
Step 4.
NG-RAN may decide to trigger EPS or inter-RAT fallback, taking into account UE capabilities, indication from AMF that "Redirection for EPS fallback for voice is possible" (received as part of initial context setup as defined in TS 38.413), network configuration (e.g. N26 availability configuration) and radio conditions. NG-RAN may initiate measurement report solicitation from the UE including E-UTRA as target.
If NG-RAN does not trigger EPS or inter-RAT fallback, then the procedure stops here and following steps are not executed.
Step 5.
NG-RAN responds indicating rejection to set up the QoS flow for IMS voice received in step 3 towards the PGW-C+SMF (or H-SMF+P-GW-C via V-SMF, in the case of roaming scenario) via AMF with and indication that mobility due to fallback for IMS voice is ongoing. The PGW-C+SMF reports the EPS Fallback event to the PCF if the PCF has subscribed to this event. The PGW-C+SMF executes the release of resources in non-3GPP AN as specified in clause 4.11.4.1 and clauses 4.9.2.1 and 4.9.2.3.
NOTE 2:
The timing of executing the release of resources in non-3GPP AN will depend on whether NG-RAN decides to trigger EPS or inter-RAT fallback but will take place at least after step 5.
If EPS fallback is triggered steps 5-7 from clause 4.13.6.1 are executed. If inter-RAT Fallback for IMS voice is triggered steps 5-6 from clause 4.13.6.2 are executed.
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4.13.7  MSISDN-less MO SMS [R16]Word-p. 281
4.13.7.1  General
The Nnef_MSISDN-less_MO_SMS service is used by the NEF to send the MSISDN-less MO SMS to the AF.
4.13.7.2  The procedure of MSISDN-less MO SMS Service
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Step 1.
The UE uses SMS over NAS procedures in clause 4.13.3 to send an SMS to the AF.
The service centre address points to the SMS-SC which contains the function described in this procedure, the destination SME address is set to short/long code of the AF and the Application Port ID element of the TP-User-Data field is set to the appropriate value.
For MSISDN-less subscription, the dummy MSISDN is used. This MSISDN and the IMSI of the UE are sent to SMS-SC.
Step 2.
SMS-SC uses the destination SME address (long/short code of the AF) to identify the corresponding NEF based on a pre-configured mapping table. SMS-SC extracts the SMS payload, Application port ID, and IMSI of the UE and delivers them to NEF along with the destination SME address (long/short code of the AF). The NEF acts as an MTC-IWF in this procedure.
Step 3.
The NEF invokes Nudm_SDM_Get (Identifier Translation, IMSI, Application Port ID, AF Identifier) to resolve the IMSI and Application Port ID to a GPSI (External Id).
Step 4.
The UDM provides a Nudm_SDM_Get response (GPSI). If the UE is not allowed to send an SMS payload to this AF, or there is no valid subscription information for this user, the flow proceeds to step 6.
Step 5.
The NEF provides a Nnef_MSISDN-less_MO_SMSNotify (SMS payload, GPSI, and Application Port ID) message to the AF. The AF is identified with the destination SME address (long/short code of the AF) received from step 2. The payload is delivered directly to the AF, it is not processed by NEF.
Step 6.
The NEF, acting as an MTC-IWF, returns a success or failure delivery indication to SMS-SC.
Step 7.
SMS-SC indicates success/failure back to UE using existing SMS delivery report defined in TS 23.040.
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4.13.8  Support of 5G LAN-type service [R16]Word-p. 282
4.13.8.1  Support of 5G VN group management
The information of 5G VN group is provided by the AF to the NEF and is stored in the UDR, by using the NEF service operations information flow procedure described in clause 4.15.6.2.
4.13.8.2  Support of 5G VN group communication
4.13.8.2.1  General
This clause specifies the procedures for 5G VN group communication.
4.13.8.2.2  group-level N4 session management procedures
The SMF shall create an group-level N4 session on the UPF for a 5G VN group when N19-based forwarding is applied. The group-level N4 Session management procedures enable the SMF to create, update or delete the group-level N4 Session, e.g. add or delete N4 rules, allocate or release the N19 tunnel resources.
In the case of N19-based forwarding is applied, the followings apply for the PDU Sessions targeting the (DNN, S-NSSAI) associated with a 5G VN group:
  • If the PDU Sessions targeting the same 5G VN group are anchored at different UPFs, the SMF shall create the group-level N4 Session in each invovled UPF via N4 Session Establishment procedure (clause 4.4.1.2) in order to establish N19 tunnel(s) between the UPFs and install the N4 rules.
  • If the last PDU Session for this 5G VN group is released on a UPF, the SMF may delete the group-level N4 Session in the UPF via N4 Session Release procedure (clause 4.4.1.4) and release the N19 tunnel(s) between this UPF and other UPF(s) serving the 5G VN group via update of the corresponding N4 rules.
  • If an address of the UE within the 5G VN group is allocated or released, the SMF may update the N4 rules(e.g. PDRs and FARs) related to the UE address into the group-level N4 Session context via N4 Session Modification procedure (clause 4.4.1.3).
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