Wi-Fi Handovers
This document outlines the Wi-Fi Handovers feature, covering its summary, description, architecture, call flows, and configuration.
Feature Summary and Revision History
Summary Data
| Applicable Product(s) or Functional Area | Applicable Platform(s) | Feature Default Setting | Related Changes in this Release | Related Documentation |
|---|---|---|---|---|
| SMF | SMI | Disabled – Configuration Required | Not Applicable | Not Applicable |
Revision History
| Revision Details | Release |
|---|---|
| TFT Handling for WiFi Handovers is supported. | 2021.01.0 |
| The Wi-Fi to 5GS Handover with EPS Fallback feature is fully qualified in this release. | 2020.02.2 |
| The Wi-Fi to 5GS Handover with EPS Fallback feature is not fully qualified in this release. For more information, contact your Cisco Account representative. | 2020.02.1 |
Feature Description
The SMF+PGW-C product supports Wi-Fi handovers. The cloud-based architecture supports the following Wi-Fi handovers in 5GS or EPS and non-3GPP untrusted access:
- EPC to non-3GPP untrusted Wi-Fi handover
- Non-3GPP untrusted Wi-Fi to EPC handover
- Non-3GPP untrusted Wi-Fi to 5GS handover with EPS fallback
- Non-3GPP untrusted Wi-Fi to 5GS handover
- 5GS to non-3GPP untrusted Wi-Fi handover
Architecture
The following sections describe the architecture for interworking between the ePDG or EPC and 5GS and the non-roaming architecture within the EPS using S5 and S2b interfaces.
ePDG and 5GS Interworking for Handover
The following figure illustrates the non-roaming architecture for interworking between the ePDG or EPC and 5GS.
[Figure 1: Non-roaming Architecture for Interworking between ePDG or EPC and 5GS - This diagram depicts the network components and interfaces involved in interworking between 5G Core (5GC) and Evolved Packet Core (EPC) with untrusted non-3GPP access like Wi-Fi.]
The interworking between the ePDG and 5GS is similar to the interworking between the EPC and 5GS without the N26 interface. In this interworking, IP address preservation occurs on the UEs during inter-system mobility. Fetching and saving the PGW-C and SMF, along with the corresponding APN and DNN information through the HSS and UDM, enables interworking. In such networks, the AMF also supports interworking with UEs without the N26 interface during initial registration in 5GC. The AMF may support interworking with UEs without N26 in the Attach procedure in 5GS. In the case of a non-3GPP untrusted Wi-Fi access, the ePDG does not communicate with the AMF because the N26 interface does not exist.
A 5GS supports network slicing and can interwork with the EPS in its PLMN or in other PLMNs. The SMF+PGW-C performs UDM registration for each UE with PGW-C FQDN and NSSAI values. With this registration, the AMF or ePDG identify the PGW-C IP address from the UDM or HSS as part of the subscription information after UE authorization is completed.
The mobility between 5GC to EPC does not ensure that all active PDU sessions can be transferred to the EPC. During PDN connection establishment in the EPC, the UE allocates the PDU session ID and sends it to the PGW-C+SMF through the PCO.
An S-NSSAI associated with the PDN connection is determined based on the operator policy by the PGW-C+SMF. For example, the combination of PGW-C+SMF address and APN is sent to the UE in the PCO along with a PLMN ID to which the S-NSSAI relates. If the PGW-C+SMF supports multiple S-NSSAIs and the APN is valid for multiple S-NSSAIs, the PGW-C+SMF selects only the S-NSSAI that is mapped to the subscribed S-NSSAIs of the UE.
The UE saves the S-NSSAI and the PLMN ID associated with the PDN connection. The UE derives the requested NSSAI through the received PLMN ID. The NAS registration request message includes the requested NSSAI. The RRC carries the registration request when the UE registers in 5GC. This scenario is applicable if the UE is non-roaming or the UE has configured NSSAI for the VPLMN in roaming case.
EPS and ePDG Interworking for Handover
The following figure illustrates the non-roaming architecture within the EPS using S5 and S2b interfaces.
[Figure 2: Non-roaming Architecture Within EPS using S5, S2a, and S2b Interfaces - This diagram illustrates the network architecture for interworking within the Evolved Packet System (EPS) using S5, S2a, and S2b interfaces.]
For 3GPP access to non-3GPP access untrusted Wi-Fi handover and for non-3GPP access untrusted Wi-Fi to 3GPP access handover, if a UE has multiple PDN connections to different APNs in the source access and the UE can route different simultaneously active PDN connections through different access networks, the UE can transfer from the source to the target access all PDN connections that were active in the source access before handover or only a subset of them. This transfer can have the restriction that multiple PDN connections to the same APN have one access.
The transfer process can occur in the following scenarios:
- 3GPP access to non-3GPP access untrusted Wi-Fi handover
- Non-3GPP access untrusted Wi-Fi to 3GPP access handover
TFT Handling for WiFi Handovers
The UE can transfer from the source to the target access all PDN connections that were active in source access before handover or only a subset of them if the following conditions are met:
- The UE has multiple PDN connections to different APNs in the source access
- The UE can route different, but simultaneously active, PDN connections through different access networks.
The SMF supports untrusted Wi-Fi access for end-users over S2b interface with ePDG after establishment of IPSec connection between the end-user and ePDG.
For untrusted Wi-Fi to EPC handover, the SMF provides a PGW-C FQDN during UDM registration and fetches the subscription information.
During UE handover, the MME fetches PGW-C FQDN from the HSS. After authentication, the MME initiates GTPv2 create session request indicating handover. The SMF+PGW-C does not perform the UDM registration and subscription procedures while processing handover request. SMF+PGW-C ensures that GTPv2 MB request indicating handover is sent to perform data path switching from untrusted Wi-Fi to EPC.
For EPC to untrusted Wi-Fi handover, the HSS provides SMF+PGW-C FQDN after the subscriber authentication. When UE performs handover, after authentication HSS provides SMF+PGW-C FQDN. The ePDG initiates GTPv2 create session request indicating handover toward PGW after IPSec tunnel establishment. SMF+PGW-C performs the UDM registration and no subscription procedures exist while processing the handover request.
TFT Handling for WiFi Handovers
In 4G and 5G deployment, for use cases like three-way audio or video multiparty call conference, and RCS messages, the PGW-C can end up having more than four filters (up to a maximum of 16 filters) for both UL and DL direction. SMF includes "EPS Bearer Level Traffic Flow Template (Bearer TFT)" in the GTPv2 CBReq/UBReq of BearerContextList. CBReq/UBReq can carry a maximum of 4 TFTs per bearer.
In the case of three-way Audio/Video and multiparty call-conference, the PCF attempts to push the pccRules by adding different subscriber TFTs in multiple "N7 Policy Notify Req" messages. The PGW-C handles the received "N7 Update Notify Req" in dedicated bearer establishment or update towards WiFi or LTE by initiating GTPv2 CBReq or UBReq messages. SMF accommodates the received SDF Filters in TFT as it never crosses more than 256 Bytes (4 TFTs).
Note: PGW-C does not support more than 4 TFTs received from PCF "N7 Policy Notify Req".
The PCF continuously pushes multiple pccRules for the same bearer by sending "N7 Policy Notify Req". Over time, the SMF may accumulate 12-16 filters for multiparty call scenarios.
When a subscriber moves from LTE to WiFi, WiFi to LTE, or NR to WiFi during handover call models, the SMF first establishes a default bearer creation as part of the handover. The SMF then attempts to send out a CBReq for Dedicated bearer establishment, accommodating all 16 filters in "EPS Bearer Level Traffic Flow Template (Bearer TFT)" of the bearer context list of the subscriber. If it fails to encode due to these restrictions, the SMF sends out CBReq without the "EPS Bearer Level Traffic Flow Template (Bearer TFT)" IE based on the HO type. The SGW/MME/ePDG then rejects the GTPv2 CBResp with "Mandatory IE Incorrect with TFT Semantic Errors".
After receiving CBResp from SGW/ePDG, the SMF does not free up policy/charging resources for the respective failed bearers, leading to further stale entries on SMF and UPF. This can result in system inconsistency for that subscriber with "EBI Mismatch – 408 Error Voice Call Failure WiFi HOs".
Standards Compliance
The Wi-Fi handovers feature complies with the following standards:
- 3GPP TS 23.502 V15.2.0 (2018-09)
- 3GPP TS 23.402 V15.3.0 (2018-03)
- 3GPP TS 29.214 V15.5.0 (2018-03)
How it Works
This section describes the Wi-Fi to LTE handover, Wi-Fi handover with EPS fallback, and Wi-Fi to 5GS handover.
EPC to Non-3GPP Untrusted Wi-Fi Handover Call Flow
This section describes the EPC to non-3GPP untrusted Wi-Fi handover call flow.
[Figure 3: EPC to Non-3GPP Untrusted Wi-Fi Handover Call Flow - This diagram illustrates the sequence of messages and interactions between network entities (UE, SGW, ePDG, SMF+PGW-C, UPF, PCF, CHF, UDM) during an EPC to untrusted Wi-Fi handover.]
| Step | Description |
|---|---|
| 1 | The UE is attached to the 3GPP access network. The SMF+PGW-C communicates with UPF, PCF, and CHF for IPv4, IPv6, or dual-stack to establish a 4G LTE PDU session. The PCF sends the Policy Control Request trigger (SM policy decision) in response to SM policy control create. The CHF provides session-level or rating-group-level triggers to the SMF in Charging Data Create response. |
| 2 | The UE connects to an untrusted non-3GPP access and an ePDG is selected through the ePDG selection process. The UE initiates the handover attach procedure as defined in 3GPP TS 23.402, section 8.6.2.1. After the IKE tunnel is established between the UE and ePDG and after the UE is authenticated over SWm interface with the AAA server, the UE initiates IKE authentication (IKE_AUTH). The IKE_AUTH includes configuration parameters of the earlier assigned IPv4 or IPv6 addresses in the EPC and P-CSCF and the DNS options. |
| 3 | The ePDG sends a Create Session Request to the P-GW. This request includes: IMSI, APN, Handover indication, RAT type, ePDG TEID of the Control Plane, ePDG address for the User Plane, ePDG TEID of the User Plane, EPS bearer identity, and User location. The RAT type indicates the non-3GPP access technology type. If the UE supports IP address preservation and it's included in the port analyzer adapter (PAA), the ePDG configures the handover indication in the Create Session Request to allow the PDN gateway to reallocate the same IP address or prefix assigned to the UE. This IP address or prefix is assigned while the UE is connected to the 3GPP IP access and initiates the policy modification procedure with PCF. |
| 4a | The SMF performs UDM registration by updating the PGW-C FQDN with UDM. UDM registration does not occur during session establishment with EPC. |
| 4b | The SMF detects charging triggers from Step 3 information against triggers received during EPC session establishment. |
| 4c | The SMF detects PCF triggers from Step 3 information against Request Policy Control triggers received during communication with PCF during EPC session establishment. |
| 5 | Based on detected armed Policy Control Triggers from Step 4b, the SMF sends the SM Policy Control Update request with detected access parameters from Step 3 to the PCF. |
| 6 | The PCF includes new or updated PCC rules and sends the SM Policy Control Update response, which contains SM policy decision information. |
| 7 | Based on information from Step 6 and existing EPC session policy data, the SMF prepares information for new or updated PCC rules. |
| 8 | If new PCC rules are received in Step 6 requiring quota information for a new Rating Group, SMF sends a Charging Update request to CHF, including new access parameters for the PDU session information. |
| 9 | CHF sends a Charging Update Response with multi-unit information containing quota information for the requested rating-group (from Step 8) and potentially for the existing rating-group of the EPC session to SMF. |
| 10 | SMF processes the information received in the Charging Update response from CHF. |
| 11 | SMF sends an N4 session modification request to UPF for the Wi-Fi tunnel. This includes details for creating uplink PDR, QER, URR for new rating-group quota information, updating URR for modified quota information, and creating FAR. |
| 12 | UPF sends the UL tunnel information (created PDR) as an N4 session modification response to SMF. |
| 13 | SMF sends the GTPv2 Create Session response to S-GW, detailing acceptance status, P-GW S2b F-TEID, PAA, APN-AMBR, bearer context creation, charging gateway address, and APCO. |
| 14 | SMF sends the GTPv2 Create Bearer request to S-GW, including bearer context list with DL tunnel information for the end-user. |
| 15 | S-GW sends the GTPv2 Create Bearer response to SMF, detailing acceptance status and bearer contexts. |
| 16 | SMF processes the Create Bearer response, derives DL tunnel information, and identifies any failed EBIs. SMF sends an N4 session modification request to UPF for the Wi-Fi tunnel to create DL PDR and DL FAR with DL tunnel information, RAT modification information, and to delete resources for the 4G tunnel. SMF also deletes N4 resources of the Wi-Fi tunnel for any failed EBI list or QFI list. |
| 17 | UPF sends the usage report as an N4 Session Modification response to SMF. |
| 18 | SMF+PGW-C sends the GTPv2 DB request to S-GW, including EBI or list of EBIs. |
| 19 | S-GW sends the GTPv2 DB response to SMF+PGW-C. |
| 20 | SMF sends a Charging Update request to CHF, including PDU session information with new access parameters and a multi-usage report of access parameters and usage report received in Step 8. |
| 21 | CHF sends a Charging Update Response with multi-unit information containing quota information for existing rating-groups to SMF. |
Non-3GPP Untrusted Wi-Fi to EPC Handover Call Flow
This section describes the non-3GPP untrusted Wi-Fi to EPC handover call flow.
[Figure 4: Non-3GPP Untrusted Wi-Fi to EPC Handover Call Flow - This diagram illustrates the sequence of messages and interactions between network entities (UE, MME, SGW, ePDG, SMF+PGW-C, UPF, PCF, CHF) during a handover from untrusted Wi-Fi to EPC.]
| Step | Description |
|---|---|
| 1 | One or more PDU sessions are established between UE and ePDG through untrusted non-3GPP access. With 5G NAS capability, ePDG selects a combined PGW+SMF. UE sends the PDU session ID to the PGW+SMF. |
| 2 | UE discovers E-UTRAN access and hands over sessions from the current non-3GPP access system to E-UTRAN. UE sends an Attach request to MME for Handover Attach request type. E-UTRAN routes messages from UE to MME as defined in 3GPP TS 23.401. UE includes an APN corresponding to PDN connections in the source non-3GPP access. |
| 3 | MME and HSS perform authentication, location update, and subscriber data retrieval for APN information. MME selects an APN, SGW, and PDN gateway as per 3GPP TS 23.401. MME sends a Create Session Request to SGW, including IMSI, MME context ID, PDN-GW address, handover indication, and APN. |
| 4 | SGW sends a Create Session Request (with handover indication) to PDN-GW in HPLMN as described in 3GPP TS 23.401. SGW sends GTPv2 Create Session Request to PDN GW, including IMSI, APN, handover indication, RAT type, S5-C TEID, S5-U TEID, EBI, and user location. RAT type indicates 3GPP IP access E-UTRAN technology. If UE supports IP address preservation (PAA), SGW configures handover indication in Creation Session Request, allowing PDN GW to reallocate the same IP address or prefix assigned to UE during 3GPP IP access. SGW initiates Policy Modification Procedure to PCF. PDN GW does not switch the tunnel from non-3GPP IP access to 3GPP access system at this point. |
| 4a | SMF does not perform UDM Registration as it occurs during Wi-Fi session establishment. |
| 4b | SMF detects charging triggers from Step 3 information against triggers received during EPC session establishment. |
| 5 | Based on detected armed Policy Control Triggers from Step 4b, SMF sends SM Policy Control Update request with detected access parameters from Step 3 to PCF. |
| 6 | PCF sends SM Policy Control Update response (SM policy decision) with new or updated PCC rules. |
| 7 | Based on information from Step 6 and existing EPC session policy data, SMF prepares information for new or updated PCC rules. |
| 8 | If SMF receives new PCC rules in Step 6, SMF sends Charging Update request to CHF with new rating-group for quota information, including PDU session information and new access params. |
| 9 | CHF sends multi-unit information as Charging Update response to SMF, including new quota information for the rating-group and existing rating-group of EPC session. |
| 10 | SMF prepares charging data from the received Charging Update Response from CHF. |
| 11 | SMF sends N4 Session Modification Request to UPF, detailing creation of UL/DL PDR, QER, URR for new rating-group quota, updated URR for modified quota, and FAR creation. |
| 12 | UPF sends UL tunnel information (created PDR) as N4 Session Modification response to SMF. |
| 13 | SMF sends GTPv2 Create Session response to S-GW, detailing acceptance status, P-GW S2b F-TEID, PAA, APN-AMBR, bearer context creation, charging gateway address, and APCO. |
| 14 | SGW sends Modification Bearer request with handover indication to PGW for data path switching from Wi-Fi tunnel to 4G tunnel. |
| 15 | PGW sends N4 Session Modification request to delete Wi-Fi tunnel and configure DL tunnel information for 4G tunnel (from Step 4). |
| 16 | UPF sends N4 Session Modification response to SMF. |
| 17 | SMF sends GTPv2 Create Session request to SGW, including bearer context list with DL Tunnel information for the end-user. |
| 18 | SGW sends GTPv2 Create Session response to SMF, detailing acceptance status and bearer contexts. |
| 19 | ePDG sends GTPv2 Create Bearer resp (accepted EBIs with DL tunnel info) to SMF. |
| 20 | SMF processes Create Bearer response, derives DL tunnel information, and identifies failed EBIs. SMF sends N4 session modification request to UPF for Wi-Fi tunnel to update DL FAR with DL tunnel info, RAT modification info, and delete resources for 4G tunnel. SMF also deletes N4 resources of Wi-Fi tunnel for failed EBI/QFI lists. |
| 21 | UPF sends usage report as N4 Session Modification Response to SMF. |
| 22 | SMF sends Charging Update request to CHF, including PDU session info with new access params and multi-usage report of old access params and usage report from Step 8. |
| 23 | CHF sends Charging Update Response with multi-unit information containing quota information for existing rating-groups to SMF. |
| 24 | SMF+PGW-C initiates GTPv2 DB Request toward SGW, including EBI or EBI list. |
| 25 | SGW sends GTPv2 DB Response toward SMF+PGW-C. |
Non-3GPP Untrusted Wi-Fi to 5GS Handover Call Flow
This section describes the non-3GPP untrusted Wi-Fi to 5GS handover call flow.
[Figure 5: Non-3GPP Untrusted Wi-Fi to 5GS Handover Call Flow - This diagram illustrates the sequence of messages and interactions between network entities (UE, AMF, ePDG, SMF+PGW-C, UPF, PCF, CHF) during a handover from untrusted Wi-Fi to 5GS.]
| Step | Description |
|---|---|
| 1 | One or more PDU sessions are established between UE and ePDG through untrusted non-3GPP access. With 5G NAS capability, ePDG selects a combined PGW+SMF. UE sends the PDU session ID to the PGW+SMF. |
| 2 | UE sends PDU Session Establishment request through 3GPP access to AMF. Request includes PDU session ID, requested PDU session type, requested SSC mode, 5GSM capability PCO, SM PDU DN request container, number of packet filters, and optional requested always-on PDU session. The request type indicates switching between 3GPP and non-3GPP access or a PDU session handover from an existing PDN connection in EPC. |
| 3 | If request type is "Existing PDU Session", AMF selects SMF based on SMF-ID from UDM. If AMF cannot identify PDU Session ID or subscription context from UDM, or if subscription profile update notification lacks SMF ID for PDU Session ID, an error occurs. AMF updates Access Type for the PDU session. If request type refers to a PDU session moved between 3GPP and non-3GPP access and S-NSSAI is available in target access's Allowed NSSAI, PDU Session Establishment is performed when SMF ID and AMF are in the same PLMN. AMF sends NSMF PDU Session Create SM Context Request to SMF with "Existing PDU Session" type, including SUPI, DNN, S-NSSAIs, PDU Session ID, AMF ID, Request Type, PCF ID, Priority Access, N1 SM container (PDU Session Establishment Request), User location info, Access Type, PEI, GPSI, Subscription For PDU Session Status Notification, DNN Selection Mode. SMF analyzes existing PDU session using SUPI+PDU-Session-ID and compares UE's IPv4/IPv6 addresses with retrieved session addresses. SMF rejects if session not retrieved or addresses do not match. |
| 4 | SMF detects PCF triggers from Step 3 information against Request Policy Control triggers received during Wi-Fi session communication with PCF. |
| 4a | SMF detects charging triggers from Step 3 information against charging triggers received during Wi-Fi session. |
| 4b | SMF does not perform UDM registration as it occurs during Wi-Fi Session Establishment. |
| 5 | SMF sends NSMF PDU Session Create SM Context response to AMF, including cause, SM Context ID or N1 SM container with PDU session rejection cause. |
| 6 | Based on detected armed Policy Control Triggers from Step 4a, SMF sends SM Policy Control Update request with detected access parameters from Step 3 to PCF. |
| 7 | PCF sends SM Policy Control Update response (SM policy decision) with new or updated PCC rules. |
| 8 | Based on information from Step 7 and existing Wi-Fi session policy data, SMF prepares information. |
| 9 | If SMF receives new PCC rules in Step 7, SMF sends Charging Update request to CHF with new rating-group for quota information, including PDU session information and new access params. |
| 10 | CHF sends multi-unit information as Charging Update response to SMF, including quota information for rating-groups from Step 9 and existing rating-group of Wi-Fi session. |
| 11 | SMF processes data from Charging Update response received from CHF. |
| 12 | SMF sends N4 session modification request to UPF for gnb tunnel, detailing creation of uplink PDR, QER, URR for new rating-group quota, updated URR for modified quota, and FAR creation. |
| 13 | UPF sends UL tunnel information (created PDR) as N4 Session Modification response to SMF. |
| 14 | SMF sends EBI assignment request to AMF, including ARP list for PDU session ID. |
| 15 | AMF sends list of EBIs as response to SMF. |
| 16 | SMF sends N1 N2 Transfer Request to AMF, including N2 message "PDU Session Resource Setup Request Transfer" with supported QFI list and UL Tunnel Information of gnb Tunnel. Also includes N1 message "PDU Session Establishment Accept" with authorized QoS rule, QoS flow description, EPCO, PDN addresses, and session AMBR values. |
| 17 | AMF sends N1 N2 Transfer acknowledgement to SMF. |
| 18 | AMF sends SM Context Update request to SMF with "PDU Session Resource Setup Response Transfer" containing failed QFI list and DL tunnel information. |
| 19 | SMF sends N4 session modification request to UPF for gnb tunnel resources to create DL PDR, DL FAR with DL tunnel info, include RAT-change details, and delete resources for Wi-Fi tunnel. SMF also deletes N4 resources of gnb tunnel for received failed QFI list. |
| 20 | UPF sends N4 Session Modification Response with usage report to SMF. |
| 21 | SMF sends SM Context Update response to AMF. |
| 22 | SMF sends Charging Update request to PCF, including PDU session info with new access params and multi-usage report with old access-params and usage report from Step 18. SMF receives Charging Update response with new quota information for existing rating-groups. |
| 23 | SMF+PGW-C initiates GTPv2 DB request, including EBIs, to ePDG. |
5GS to Non-3GPP Untrusted Wi-Fi Handover Call Flow
This section describes the 5GS to non-3GPP untrusted Wi-Fi handover call flow.
[Figure 6: 5GS to Non-3GPP Untrusted Wi-Fi Handover Call Flow - This diagram illustrates the sequence of messages and interactions between network entities (UE, AMF, ePDG, SMF+PGW-C, UPF, PCF, CHF) during a handover from 5GS to untrusted Wi-Fi.]
| Step | Description |
|---|---|
| 1 | The UE and SMF or UPF interact through NG-RAN to establish one or more PDU sessions. |
| 2 | UE connects to untrusted non-3GPP access and selects an ePDG. UE initiates handover attach procedure (3GPP TS 23.402, section 8.6.2.1). After establishing IKE tunnel between UE and ePDG, and authenticating UE over SWm interface with AAA server, UE initiates IKE_AUH. IKE_AUH includes cfg_params of earlier assigned IPv4/IPv6 addresses in 5GS, P-CSCF, and DNS options. |
| 3 | ePDG sends Create Session request to P-GW, including: IMSI, APN, handover indication, RAT type, ePDG TEID of control plane, ePDG address for user plane, ePDG TEID of user plane, EPS bearer identity, user location. RAT type indicates non-3GPP access technology. If UE supports IP address preservation (PAA), ePDG configures handover indication in Create Session request, allowing P-GW to reallocate same IP address or prefix assigned to UE during 3GPP IP access. Policy modification procedure begins with PCF. |
| 4 | SMF does not perform UDM registration as it's already registered with UDM during 5GS session establishment. |
| 4a | SMF detects charging triggers from Step 3 information against triggers received during Wi-Fi session. |
| 4b | SMF detects policy triggers from Step 3 information against requested policy control triggers received during Wi-Fi session establishment communication with PCF. |
| 5 | Based on detected armed Policy Control Triggers from Step 4b, SMF sends SM Policy Control Update request with detected access parameters from Step 3 to PCF. |
| 6 | PCF sends SM policy decision in SM Policy Control Update response, including new or updated PCC rules. |
| 7 | Based on information from Step 6 and existing 5GS session policy data, SMF prepares "ModPolData" information. |
| 8 | If SMF receives new PCC rules in Step 6, SMF sends Charging Update request to CHF with new rating-group for quota information, including PDU session information and new access parameters. |
| 9 | CHF sends multi-unit information as Charging Update response to SMF, including quota information for rating-groups from Step 8 and existing rating-group of 5GS session. |
| 10 | SMF processes ModChargingData in Charging Update response received from CHF. |
| 11 | SMF sends N4 session modification request to UPF for Wi-Fi tunnels, detailing creation of uplink FAR, QER, URR for new rating-group quota, update on URR for modified quota, and FAR creation. |
| 12 | UPF sends UL tunnel information (created PDR) as N4 Session Modification response to SMF. |
| 13 | SMF sends GTPv2 Create Session response to S-GW, detailing acceptance status, P-GW S2b F-TEID, PAA, APN-AMBR, bearer context creation, charging gateway address, and APCO. |
| 14 | SMF sends GTPv2 Create Bearer request to S-GW, including bearer context list with UL tunnel information for each dedicated bearer to end-user. |
| 15 | S-GW sends GTPv2 Create Bearer response to SMF, detailing acceptance status and bearer contexts. |
| 16 | SMF processes Create Bearer response, derives DL tunnel information for established bearer, and identifies failed EBI list. SMF sends N4 session modification request to UPF for Wi-Fi tunnel to create DL PDR and DL FAR with DL tunnel information or list of charging description IDs for detected charging triggers. SMF deletes gnb tunnel resources and N4 resources of Wi-Fi tunnel for failed bearer context list. |
| 17 | UPF sends usage report in N4 Session Modification response to SMF. |
| 18 | SMF initiates NAMF communication N1 N2 message transfer to S-GW, including PDU Session Resource Release Request N2 message. |
| 19 | AMF sends N1 N2 Transfer Acknowledgement to SMF. |
| 20 | AMF sends SM Context Update request to SMF, including SM Resource Release Acknowledgement N2 message. |
| 21 | SMF sends 200/204 OK as SM Context Update response to AMF. |
| 22 | AMF sends SM Context Update request to SMF, including PDU Session Release Complete N1 message. |
| 23 | SMF sends 200/204 OK as SM Context Update response to AMF. |
Non 3GPP Untrusted LTE to WiFi Handover
This section describes the non-3GPP untrusted LTE to WiFi handover call flow.
[Figure 7: Non-3GPP Untrusted LTE to WiFi Handover with TFTs more than 4 for a Dedicated Bearer - This diagram illustrates the sequence of messages and interactions between network entities (UE, MME, SGW, ePDG, PGW-C, PCF, LRF, CHF) during an LTE to Wi-Fi handover with more than 4 TFTs for a dedicated bearer.]
| Step | Description |
|---|---|
| 1 | Session established in LTE with a default bearer and dedicated bearer with 8 TFTs. |
| 2 | LTE->Wi-Fi Handover triggered, when CSReq is received with hi flag set from ePDG. |
Configuring the WiFi Handovers Feature
This section describes the configurations related to the Wi-Fi Handovers feature.
Configuring Compliance Profile
The SMF provides compliance profile support for the 3GPP specification 23.502 through CLI configuration. This compliance profile is used during the 5GS to non-3GPP untrusted WiFi handover procedure.
Use the following configuration to configure the SMF in compliance with the 3GPP specification:
configure profile compliance profile_name service threegpp23502 version spec spec_version full version_format uri_version uri_version range ! ! NOTES: • full: Specifies the full version in the format <Major-version>.<Minor-version>.<patch-version>.[alpha-<draft-number>] • spec: Specifies the 3GPP specification version number. It can be one of the following values: • 15.4.0 • 15.6.0
To support 3GPP December 2018 specification compliance, configure the specification version as 15.4.0. The default version is 15.4.0.
To support 3GPP June 2019 specification compliance, configure the specification version as 15.6.0.
• uri: Specifies the URI version in the format - "v" concatenated with a number. It can be both v1 and v2, or either v1 or v2.
