# Summary of S4-260261: Conference Application Scenario for QUIC-based RTC

## Document Information
- **Source:** InterDigital
- **Title:** Application scenario: Conference using QUIC-based media protocols for RTC
- **Specification:** 3GPP TR 26.836 v0.0.1
- **Purpose:** Discussion and Agreement

## Introduction and Objective

This contribution addresses the Study on QUIC-based media delivery for real-time communication and services (FS_Q4RTC_MED). The focus is on identifying and documenting relevant application scenarios for evaluating QUIC-based media delivery protocols, specifically for conference applications in real-time communication services.

## Main Technical Contributions

### Reference Updates

Addition of normative reference:
- **[X.1] 3GPP TR 22.870:** "Study on 6G Use Cases and Service Requirements"

### Conference Application Scenario (Section 5.2.1.X)

#### General Description

The contribution defines a conference application scenario enabling multiple UEs (smartphones, tablets, smart glasses) to participate in real-time interactive sessions from web-based or native clients. Key characteristics include:
- Support for audio, video, haptic media and data sharing (chat, presence, screen-sharing metadata)
- Reliable control signaling and non-media data
- Low latency and continuity prioritization for media delivery
- Support for different browsers and dedicated applications

#### Architecture 1: Single Output Scenario with Centralized Mixing (Section 5.2.1.X.2)

**Architecture characteristics:**
- Media streams (audio/video/haptic) from all participants sent to central conferencing server
- Server includes composition function/media mixer
- Mixer combines different input streams into single composite output stream per session
- All UEs receive identical combined/mixed streams
- Control and signaling messages exchanged between UEs and conferencing server

**Functional aspects:**
- Capability and state exchange between all parties
- Dynamic adaptation by media mixer to changes (resolution, video source)
- Server manages admission of new participants

#### Architecture 2: Multi-Stream Scenario (Section 5.2.1.X.3)

**Architecture characteristics:**
- Participants subscribe to audio/video streams published by remote participants
- Central conferencing server manages subscription and publish mechanisms
- Dynamic subscription model: UEs can subscribe to one or more streams, changeable over time
- Composition performed on UE side

**Example scenarios:**
- UE1 subscribes to all audio and video streams from other UEs
- UE2 subscribes selectively (e.g., video from UE1, audio from UE1/UE3/UE4)
- Dynamic changes supported (e.g., UE2 later subscribes to UE4 video)

### Mapping to TR 22.870 Use Cases (Section 5.2.1.X.4)

The contribution maps the two conference architectures to specific use cases from TR 22.870:

#### Multi-Stream Scenario Mapping:
- **Holographic telepresence in healthcare (clause 9.8):** Separate streams for audio, hologram (avatar), and haptics with tight inter-stream synchronization

#### Single Output Scenario Mapping:
- **Multi-site immersive communication (clause 9.6):** Multi-camera capture with central rendering of global scene, distributed to on-site audiences and remote viewers

#### Additional Relevant Use Cases:

1. **Immersive gaming (clause 9.2):** Conversational media, interactive XR, haptics, synchronized shared state
2. **Seamless immersive reality in education (clause 9.5):** Real-time immersive telepresence with conversational latency and tight media synchronization
3. **Collaborative service in multi-site involved immersive communication (clause 9.6):** Multi-site immersive communication with stringent latency, synchronization, and uplink requirements
4. **Multiple application media synchronisation (clause 9.7):** Ultra-tight real-time, multi-modal communication with millisecond-level cross-flow and cross-device synchronization
5. **Mixed reality gaming (clause 9.9):** Interactive real-time mixed reality with low latency and bidirectional data exchange
6. **Personalised interactive immersive guided tour (clause 9.12):** Interactive, multi-user real-time immersive communication with personalized content and tight multi-modal synchronization

### QUIC Protocol Suitability Justification

The contribution provides rationale for QUIC-based transport for immersive use cases based on alignment with TR 22.870 requirements:

**Key requirements addressed:**
- Low latency
- Bidirectional communication
- High reliability
- Multi-modal traffic support
- Strong security

**QUIC protocol advantages:**
- Encrypted-by-default communication
- Stream multiplexing without head-of-line blocking
- Robustness to packet loss and network variability
- Built-in standardized congestion control and loss recovery mechanisms

These characteristics make QUIC suitable for interactive and immersive communication application scenarios.