Summary of S4-260187: On Mapping to 3DGS Services

1. Introduction and Background

This contribution from Nokia addresses objectives 3 and 5 of the FS_3DGS_MED study (approved in SP-251190 at SA#109). The objectives include:

• Objective 5: Mapping relevant workflows to 3GPP services
• Objective 3: Studying content generation aspects including network-based processing and Edge/Cloud operations for 3DGS representations

The document notes that static 3DGS content generation workflow (documented in draft TR 26.958v0.1.0) consists of:
- Capture
- Structure from Motion (SfM) estimation for sparse point cloud reconstruction
- Gaussian initialization
- Training and optimization

The contribution emphasizes that SfM and training are compute-heavy operations requiring architectural consideration. The document reviews two SA4 media service architectures as potential frameworks: the 5G Media Delivery architecture (TS 26.501, TS 26.510) and IMS (TS 23.228, TS 26.114), noting precedents from R18/R19 services like split rendering, avatar communications, media messaging, and spatial computing.

2. Media Service Enabler (MSE) Framework

Architecture Overview

The contribution proposes leveraging the MSE framework (TR 26.857) which provides Application Providers with well-defined client and network-side functions. The reference architecture includes:

Defined Functions:
- Application: UE-resident function leveraging MSE
- MSE Client: Logical internal UE function for specific MSE
- MSE Application Function (AF): Dedicated application function for an MSE
- MSE Application Server (AS): Dedicated application server for an MSE

Defined Interfaces/APIs:
- MSE-1: Provisioning API for Application Providers
- MSE-2: Optional ingest/egest API for content processing
- MSE-3: Inter MSE AF-MSE AS communication
- MSE-4: User plane interface between MSE Client and Server
- MSE-5: Control API for configuration and management
- MSE-6: Client APIs for internal application communication
- MSE-7: External device APIs for accessing device functions
- MSE-8: Application APIs for information exchange between Application and Provider

3DGS Workflow Mapping to MSE

The proposed mapping for 3DGS content generation and sharing:
- AP provisions service through MSE-1
- Session handling control plane information exchanged between MSE AF and MSE client over MSE-5
- Media communication over MSE-4
- Application uses device functions (cameras) via MSE-7 to capture images/video
- Captured media transmitted over MSE-4 to MSE AS for SfM and training
- Generated 3DGS or rendered views shared back to UE over MSE-4

3. IMS Data Channel (IMS DC) Architecture

Architecture Overview

The contribution proposes IMS DC (TS 23.228 Annex AC) as an alternative architecture, noting IMS as the backbone for conversational media in 3GPP networks.

New Functional Entities:
- Data Channel Signalling Function (DCSF): Manages data channel control logic, determines service availability, manages bootstrap and application data channel resources at MF via IMS AS, handles interworking between application data channel media and audio/video media
- Media Function (MF): Provides media resource management and forwarding of data channel media traffic, manages bootstrap and application data channel resources, anchors application data channels in P2P scenarios, relays traffic between UEs and DC-AS, handles transcoding. SA2 specifies MF supports rendering (S4-251420) but not AIML functionality (S4-260022)
- DC Application Repository (DC-AR): Stores verified data channel applications for retrieval by DCSF and download to UE
- DC Application Server (DC-AS): Interacts with DCSF for resource control and traffic forwarding, serves as endpoint for application data channels, communicates with UE through MF. DC-AS functionalities are not 3GPP-specified

DC-Relevant Reference Points:
- DC1: Between DCSF and IMS AS
- DC2: Between IMS AS and MF
- DC3: Between DCSF and NEF
- DC4: Between DCSF and DC Application Server
- DC5: Between DCSF and DCAR
- N70/Cx/Dx: Between CSCF and HSS (updated for DC signalling)
- N71/Sh: Between IMS AS and HSS (updated for DC signalling)

Data Channel Media Handling Reference Points:
- MDC1: Between MF and DCSF
- MDC2: Between MF and DC-AS, between BAR and DC-AS, between MF and BAR
- MDC3: Between DCSF and DC-AS

3DGS Workflow Mapping to IMS DC

The proposed mapping for 3DGS generation over IMS DC:
- Service provider provides IMS DC application to DCAR
- Provisions and configures resources via NEF and DC4
- UE downloads IMS DC app
- IMS DC app sets up application data channel with DC-AS for service configuration
- Uses device camera(s) to capture images/video
- Transmits captured media to DC-AS for SfM and 3DGS training
- Generated 3DGS shared back to UE or sent to MF for view-based rendering

4. Conclusion and Proposal

The contribution proposes to develop mappings for 3DGS content generation and sharing workflows to both an MSE framework and to IMS DC architecture, considering both frameworks appropriate for 3DGS service deployment.