5.37.9.2 Usage of Media over QUIC in order to Handle end-to-end encrypted XR and media flows

When a PSA UPF that supports MoQ relay functionality has been selected, encrypted Metadata associated with traffic can be transported between the UPF and the AS via Media over QUIC (MoQ), IETF draft-ietf-moq-transport [201].

A PSA UPF supporting the MoQ relay functionality can be selected by SMF with the consideration of the DNN and S-NSSAI provided by UE.

NOTE 1: The application client in the UE uses MoQ Transport protocol and establishes a MoQ connection using the address of MoQ relay between the application client and MoQ relay in UPF as defined in MoQ, IETF draft-ietf-moq-transport [201].

The SMF may get the address of MoQ relay from the UPF during N4 session management procedure as defined in the clause 4.4.1 of TS 23.502 [3]: the SMF indicates the PSA UPF to provide MoQ relay address in N4 Session Establishment/Modification Request and the PSA UPF returns MoQ relay address in N4 Session Establishment/Modification Response.

NOTE 2: The application client can obtain the MoQ relay address via application layer-based schemes.

In the case the EASDF based DNS procedure as described in clause 6.2.3.2.2 of TS 23.548 [130] is used, after SMF has received FQDN in DNS message report from EASDF, if SMF determines that the FQDN is for MoQ traffic, then SMF gets the address of MoQ relay from UPF and then SMF provides DNS message handling rule with the address of MoQ relay to instruct EASDF to return the address of MoQ relay in PSA UPF by setting the Forwarding Action as Respond directly to the DNS request according to TS 23.548 [130]. In this case a local PSA UPF supporting MoQ relay maybe selected by SMF.

NOTE 3: It is assumed an application client can send a DNS query to resolve FQDN.

NOTE 4: The FQDN can be the FQDN for MoQ traffic and preconfigured in SMF or it can be the FQDN of the MoQ relay and preconfigured in SMF and application client. It is assumed there is SLA between operator and application service provider for using MoQ relay functionality provided by operator.

NOTE 5: In some other case, the application client can also obtain the MoQ relay FQDN or IP address from the MoQ application server via the query during the MoQ session establishment between the application client and the MoQ application server as in MoQ, IETF draft-ietf-moq-transport [201], which is out of the scope of 3GPP. The MoQ application server can get the MoQ relay FQDN or IP address via local configuration.

NOTE 6: Different MoQ application servers can correspond to different MoQ relays that are deployed on the same PSA UPF.

The AF provided Protocol Description indicating Media over QUIC Transport, IETF draft-ietf-moq-transport [201] can be used in determining the PCC Rule by the PCF as defined in clause 6.1.3.27.4 of TS 23.503 [45]. Based on the PCC rule, the SMF generates the PDU Set Information marking Indicator to instruct the PSA UPF to perform PDU Set Information identification. Upon receiving the MoQ SUBSCRIBE message from UE application client, the MoQ relay can establish an upstream MoQ subscription to the MoQ application server if there is no existing subscription yet.

For the downlink service data flow packet using MoQ Transport, based on the Indicator received from SMF, the PSA UPF can identify the PDU Set Information from the MoQ Metadata as defined in clause 9 of MoQ, IETF draft-ietf-moq-transport [201] that is extracted from the received data packet by the MoQ relay and provide the PDU Set Information to the RAN by adding it in the GTP-U header.

NOTE 7: The format of the MoQ Metadata carrying the media related information and transported in the MoQ object extension header(s) is defined in TS 29.561 [132]. Moreover, the mappings between the MoQ Metadata and the media related information can be based on local configuration, or operator-determined implementations.