Technical Summary of S4-260255: Application-Layer Approaches for Multi-Access Media Delivery

Document Overview

This document is a partial Change Request (pCR) for 3GPP TR 26.804 that proposes updates to enable multi-access media delivery using application-layer approaches, specifically focusing on Common Media Client Framework (CMMF). It is intended to be merged with CR 0036 as part of the FS_AMD_Ph2 feasibility study.

Main Technical Contributions

1. Application-Layer Multi-Access Using CMMF (Clause 5.18.1.2)

1.1 Introduction to Upper Layer Approaches

The document introduces two application-layer methods for multi-access media delivery without requiring lower-layer support like ATSSS:

• Multipath transport protocols (MPTCP, MPQUIC) - requires implementation on both UE and Application Server
• CMMF-based approach - allows transport layer, network layer, and Application Server to remain agnostic of multi-access usage

Both approaches use multiple TCP/QUIC connections bound to different UE network interfaces, with traffic steering performed using existing UE and network functionality.

1.2 CMMF-Specific Implementation

Key characteristics:
- Media encoded within CMMF bitstreams/transport objects made available at one or more service locations
- No changes required to CMMF bitstream/transport object creation or network provisioning
- No network/transport layer support (multipath protocols, ATSSS) required
- Clients only need capability to communicate over multiple access networks and steer traffic
- Operation over one access network largely independent of others

Deployment scenarios:
- Scenario 1: Multiple service locations, each serving requests over specific access network
- Scenario 2: Single service location delivering CMMF-encoded media across both access networks

In both scenarios, different CMMF-encoded representations (e.g., CMMF-A and CMMF-B) are requested over different access networks.

Traffic steering mechanism:
- Multiple HTTP clients (one per access network) bound to different network interfaces
- HTTP requests/responses automatically routed over bound interface/access network

1.3 Performance Results

The document includes experimental results showing:
- Stable playback bitrate maintained despite WLAN degradation
- Healthy playback buffer maintained throughout session
- Seamless transition from WLAN to 5G cellular as WLAN quality degraded
- Dynamic adaptation of download distribution across access networks based on connection quality

2. Architecture Mapping (Clause 5.18.3.1)

Updates to architecture mapping:
- Expands upon architecture mappings from clause 5.19.3
- Media Access Client has capability to steer network traffic to different UE network interfaces/access networks
- Can switch between access networks or use both simultaneously
- When using CMMF, different CMMF representation/variation retrieved over each access network
- CMMF decoder (sub-component of Media Access Client) recovers requested media resource

Key architectural point:
- Reference point M4d defined over both 3GPP and non-3GPP access networks
- Media Access Client architecture not normatively specified in 5GMS System
- No changes to 5GMS architecture anticipated

3. High-Level Call Flow (Clause 5.18.4.1)

Procedure assumptions:
- Media Player has functionality to stream from multiple service locations and/or across multiple access networks
- Capabilities include: switching between service locations, concurrent use of multiple service locations, steering network traffic, concurrent use of multiple access networks
- Configuration information available via Media Player Entry document or referenced documents
- Content may be hosted at multiple service locations (inside or outside 5GMS System)
- Content may be streamed over two or more access networks

Key procedure updates:
- Step 1: Content available from two or more service locations
- Step 11: Media Player determines multiple service location configuration and method of access
- Step 15: Transport sessions established over different access networks based on UE connection and Media Player capabilities
- Steps 17-18: Initialization information and media segments may be obtained over one or more access networks

4. Gap Analysis (Clause 5.18.5.1)

Identified open issues:

1. Existing downlink media streaming procedures in TS 26.501 don't address multi-access downlink media streaming using application-layer approaches
2. Media Access Client capability to use multiple access networks without lower-layer multipath support not addressed in 5GMS stage-3 specifications
3. CMMF procedures, protocols, and formats not defined for downlink media streaming over multiple access networks in TS 26.512

5. Candidate Solutions (Clause 5.18.6.1)

5.1 General Use Cases

Application-layer approaches may be used when:
- 5GMSd Application Provider wants to influence how connections to multiple access networks are used
- Using multiple access networks to access media hosted at different service locations
- Transport/network-layer multi-access protocols (MPTCP, ATSSS, etc.) not supported by 5GMSd Client or AS

5.2 CMMF-Based Solution

Approach:
- 5GMSd Client accesses/downloads CMMF-encoded media objects over multiple access networks simultaneously from single 5GMSd AS
- Multiple different CMMF-encoded bitstreams/objects (representations/stripes) stored/cached within single logical 5GMSd AS
- Different CMMF-encoded representation downloaded over each available access network
- CMMF decoder yields original source content once enough information received

Key differentiator from other multi-access technologies:
- Responsibility for setup, request, and steering rests with application layer (Media Player)
- Multiple HTTP connections in parallel, each bound to different network interface
- HTTP responses routed appropriately following standard network-layer/IP routing

Traffic steering policies:
- Best-effort policy: Download as much CMMF-encoded content from each access network until decoder can successfully decode
- Preference policy: Scheduler throttles requests over one access network to preference another

Proposed changes:

1. Define mapping of application-layer approaches into 5GMS procedures in TS 26.501 for multi-access network delivery using CMMF
2. Define procedures, protocols, and formats in Annex H of TS 26.512:
3. Specify media player requirements/recommendations for multi-access delivery using CMMF (including capability to select and steer network traffic)
4. Specify use of CMMF delivery conformance profile
5. Provide recommendations for constructing CMMF Media Player Entries for multiple access networks

6. Summary and Conclusions (Clause 5.18.7)

Recommendations:

1. For TS 26.501 - Add informative annex documenting:
2. Brief description of multi-access media delivery
3. Mapping of ATSSS architecture into 5GMS architecture

4. Mapping of application-layer approaches into 5GMS procedures for CMMF-based multi-access delivery

5. For TS 26.510 - Implement changes to Configuration Settings API and Dynamic Status Information API for application configuration and status information exchange

6. Future study should examine:

7. Whether future ATSSS work supports traffic splitting for GBR QoS Flows
8. Impact on splitting M4 media flows if transported as GBR QoS Flows
9. Impact on UE multi-path management, Dynamic Policy, Network Assistance, and network slicing procedures

10. Closer alignment with study on media delivery from multiple service endpoints/locations

11. For TS 26.512 - Update Annex H procedures, protocols, and formats to enable application-layer multi-access media delivery using CMMF

7. Overall Conclusions (Clause 6.18)

Stage-2 recommendations:
- Add informative annex to TS 26.501 with multi-access media delivery description, ATSSS architecture mapping, and application-layer approaches mapping

Stage-3 recommendations:
- Implement API changes in TS 26.510
- Update Annex H of TS 26.512 for CMMF-based multi-access delivery

Future work:
- Monitor ATSSS specification work in TS 23.501 and TS 23.502
- Study impact on UE multi-access path management, Dynamic Policies, Network Assistance, and network slicing procedures