VoWiFi Support

Feature Summary and Revision History

Summary Data

Table 1. Summary Data

Applicable Product(s) or Functional Area

SMF

Applicable Platform(s)

SMI

Feature Default Setting

Disabled – Configuration Required

Related Changes in this Release

Not Applicable

Related Documentation

Not Applicable

Revision History

Table 2. Revision History

Revision Details

Release

First introduced.

Pre-2020.02.0

Feature Description

The SMF supports Voice over Wi-Fi (VoWiFi). The VoWiFi technology provides the telephony services using Voice over IP (VoIP) from the mobile devices that are connected across a Wi-Fi network.

Architecture

This section describes the VoWiFi architecture.

Figure 1. VoWiFi Architecture

How it Works

A 5G mobile device connects through an untrusted Wi-Fi network for voice services to establish a PDN connection with PGW-C. This connection is established through Internet Key Exchange Protocol version 2 (IKEv2) protocol between the UE and enhanced Packet Data Gateway (ePDG). The P-GW receives the GTPv2 Create Session Request from an untrusted Wi-Fi ePDG over the S2b interface. The PGW-C then communicates with the SBI interfaces for creating the default and dedicated bearers. The SBI interfaces can be an N7, N10, N40, or an NRF interface.

Call Flows

This section describes the following call flows:

  • VoWiFi PDU Session Creation Call Flow

  • VoWiFi Mobile-Originated (MO) Call Creation Call Flow

  • VoWifi Mobile-Terminated (MT) Call Creation Call Flow

VoWiFi PDU Session Creation Call Flow

To enable connectivity through a 5G core, the initial attach on the ePDG or EPS deviates from the defined 3GPP procedures in the following ways:

  • An SMF+P-GW replaces the P-GW in the procedure.

  • The SM Policy Association Establishment procedure replaces the IP-CAN Session Establishment and modification.

  • The integrated charging over the NCHF interface with CHF replaces the online and offline charging functionality by using the Gy and Gz interfaces.

  • Communication with the User Plane node happens over the N4 interface instead of the Sxb interface.

The following call flow depicts the creation of a VoWifi PDU session.

Figure 2. VoWiFi PDU Session Creation Call Flow
Table 3. VoWiFi PDU Session Creation Call Flow Description
Step Description
1

The UE initiates the IKE_SA_INIT and IKE_SA_AUTH exchange.

The UE then sends the IKE_SA_AUTH exchange message to ePDG to create the IPSec tunnel.
2 The UE sends the IKE_SA_AUTH exchange message to the SMF+PGW-C as a GTP Create Session Request by including the “P-CSCF IPv4 or IPv6 request and DNS IPv4 or IPv6” container identifier in APCO IE Options.
3 The SMF+PGW-C extracts and saves the PDU Session ID that the UE sent in the APCO IE option. The SMF+PGW-C then performs a UDM registration and sends both the N11 and S2b interface IDs to UDM. Based on the local configuration or session management subscription data that is received from UDM for respective DNN, SMF+PGW-C determines to support “IMS Voice over PS”.
4

The SMF+PGW-C sends the NPCF SM Policy Control Creation Request to the PCF to initiate the SM Policy Association Establishment procedure. In this procedure, the PGW-C+SMF includes the information elements that are received in the Create Session Request message into the Npcf_SMPolicyControl_Create service. These elements comprise the following information:

  • SUPI contains the IMSI.

  • DNN contains the APN.

  • PEI contains the IMEI-SV.

  • Session AMBR contains the APN-AMBR.

  • Default QoS information that contains the default EPS bearer QoS. The QCI values are mapped into 5QI values.

5 The PGW-C+SMF receives the PCC rules, PDU session policy information, and 5G QoS information. The PCC rules are mapped into EPS QoS information. The SMF+PGW-C creates TFT from the SDF filters that are received in the PCC rules. The SMF+PGW-C then associates them with the corresponding default and dedicated bearers.
6 Based on the charging policies received from the PCF, the SMF+PGW-C initiates Nchf_ConvergedCharging_Create procedure toward CHF. This procedure is based on the charging rules that are received from the PCF.
7 The SMF+PGW-C starts the UPF+PGW-U selection and N4 Session Establishment procedure. As this session is a 4G session that connects to the SMF+PGW-C, a separate CN tunnel is created for each bearer. Also, the QoS Flow Identifier (QFI) is not sent in the QoS Enforcement Rule (QER) and Packet Detection Rule (PDR).
8 Th eSMF+PGW-C sends Create Session Response to the ePDG. This response includes the bearer information and the TEID for the default bearer. The SMF+PGW-C also includes the 5G QoS parameters in APCO options 001CH (QoS rules), 001DH (Session-AMBR), 001EH (PDU session address lifetime), and 001FH (QoS flow descriptions) to the UE.
9

The ePDG sends IKE_SA_AUTH Response to the UE.

Then, depending on the mapped PCC rules, the SMF+PGW-C initiates the dedicated bearer creation.

VoWiFi Mobile-Originated (MO) Call Creation Call Flow

This section describes the VoWiFi MO call creation call flow.

Figure 3. VoWiFi MO Call Creation Call Flow
Table 4. VoWiFi MO Call Creation Call Flow Description
Step Description
1 UE requests for establishment of the IMS default bearer, PDU session, through PCF. After establishing the session, the UE receives the P-CSCF addresses from PCF.
2 The UE initiates the SIP signaling toward P-CSCF (AF).
3 The P-CSCF (AF) sends the NPCF Policy Authorization Update message to the PCF.
4 The PCF sends the NPCF SM Policy Control Update Notify Request to the SMF+PGW-C.
5 The SMF+PGW-C sends the NPCF SM Policy Control Update Notify Response back to the PCF.
6 SMF sends ChargingDataUpdateReq by including Multi-Unit-Usage with Rating-Group-Id that are received as part of Charging_Description of Sm_PolicyControl_UpdateNotify_Request to install PCC Rules.
7 CHF provides ChargingDataUpdateResp with Multi-Unit-Information for received Rating-Group values in requested message. CHF also provides params changes for Session-Level and Rating-Group values.
8 SMF sends N4 Session Modification Request to the UPF by including Create ULPDRs and Create ULFARs. Create ULPDRs include SDFs and QER Info which are received as part of PCC Rule Installation.
9 UPF responds back with N4 Session Modification Response to SMF by including Created ULPDR and Created ULFAR. Create ULFAR contains UL Tunnel Information of UPF for the dedicated bearer creation.
10 The SMF+PGW-C sends the GTPv2 Create Bearer Request to the S-GW.
11 The S-GW sends the GTPv2 Create Bearer Request to the ePDG.
12 IKE_CHILD_SA exchange happens between the UE and ePDG.
13 The ePDG sends the GTPv2 Create Bearer Response back to the SMF+PGW-C.
14 The established N4 session is modified between SMF+PGW-C and UPF+PGW-C.
15 The SMF+PGW-C sends the NPCF SM Policy Control Update Request to the PCF.
16 The PCF sends the NPCF SM Policy Control Update Response back to the SMF+PGW-C.
17 PCF sends the NPCF policy authorization notify request to P-CSCF (AF).
18 Establishes SIP-signaling and voice call between end-users through UE and P-CSCF (AF).

NOTE:

  • The PCC rules that the PCF provides are mapped to TFTs for the new dedicated bearer. The associated QoS is mapped to 4G QoS.

  • The NCHF Converged Charging Update Service procedures replace all the Gy and Gz interface messages.

  • The User Plane resources for dedicated bearers are added through the N4 Session Modification procedure towards the UPF. PDRs, QERs, and FARs are added for the SDF filters for the new dedicated bearer.

  • The SMF+PGW-C saves the EBI for the dedicated bearer that is received in the Create Bearer Response.

VoWifi Mobile-Terminated (MT) Call Creation Call Flow

This section describes the Mobile-Terminated (MT) call flow.

Figure 4. VoWifi MT Call Creation Call Flow
Table 5. VoWifi MT Call Creation Call Flow Description
Step Description
1 UE requests for establishment of the IMS default bearer, PDU session, through PCF. After establishing the session, the UE receives the P-CSCF addresses from PCF.
2 The UE-initiates the SIP signaling towards the P-CSCF (AF).
3 The P-CSCF (AF) sends the NPCF Policy Authorization Update message to the PCF.
4 The PCF sends the NPCF SM Policy Control Update Notify Request to the SMF+PGW-C.
5 The SMF+PGW-C sends the NPCF SM Policy Control Update Notify Response back to the PCF.
6 SMF sends ChargingDataUpdateReq by including Multi-Unit-Usage with Rating-Group-Id that are received as part of Charging_Description of Sm_PolicyControl_UpdateNotify_Request to install PCC Rules.
7 CHF provides ChargingDataUpdateResp with Multi-Unit-Information for received Rating-Group values in requested message. CHF also provides params changes for Session-Level and Rating-Group values.
8 SMF sends N4 Session Modification Request to the UPF by including Create ULPDRs and Create ULFARs. Create ULPDRs include SDFs and QER Info which are received as part of PCC Rule Installation.
9 UPF responds back with N4 Session Modification Response to SMF by including Created ULPDR and Created ULFAR. Create ULFAR contains UL Tunnel Information of UPF for the dedicated bearer creation.
10 The SMF+PGW-C sends the GTPv2 Create Bearer Request to the S-GW.
11 The S-GW sends the GTPv2 Create Bearer Request to the ePDG.
12 IKE_CHILD_SA exchange happens between the UE and ePDG.
13 The ePDG sends the GTPv2 Create Bearer Response back to the SMF+PGW-C.
14 The established N4 session is modified between SMF+PGW-C and UPF+PGW-C.
15 The SMF+PGW-C sends the NPCF SM Policy Control Update Request to the PCF.
16 The PCF sends the NPCF SM Policy Control Update Response back to the SMF+PGW-C.
17 PCF sends the NPCF policy authorization notify request to P-CSCF (AF).
18 Establishes SIP-signaling and voice call between end-users through UE and P-CSCF (AF).

Standards Compliance

The VoWiFi support feature complies with the following standard:

  • 3GPP TS 23.502 V15.2.0 (2018-09)

Limitations

In this release, the VoWiFi support feature has the following limitations:

  • UE-initiated Dedicated Bearer Creation is not supported.

  • VoWiFi is not integrated with charging.

  • PCF-initiated modification is not supported to change the GBR flows and PCC rules. However, the addition and deletion of GBR flows are supported.

  • Integration of charging is not supported.