# Summary of 3GPP Change Request S4-260257

## Document Information
- **Source:** InterDigital Pennsylvania
- **Title:** WebTransport protocol for real-time communication
- **Specification:** 3GPP TR 26.836 v0.0.1
- **Study:** FS_Q4RTC_MED (Study on QUIC-based media delivery for real-time communication and services)

## Purpose
This CR documents the WebTransport media delivery protocol, including its features, benefits, and limitations for use in real-time communication services within the ongoing study on QUIC-based media delivery protocols.

## Technical Contributions

### Reference Updates
The CR adds six new normative/informative references related to WebTransport:
- IETF draft-ietf-webtrans-overview (WebTransport Protocol Framework)
- IETF draft-ietf-webtrans-http3 (WebTransport over HTTP/3)
- IETF draft-ietf-webtrans-http2 (WebTransport over HTTP/2)
- WebTransport API (MDN documentation)
- W3C Working Draft for WebTransport
- IETF WebTransport Working Group Charter

### New Technical Clause: WebTransport (4.2.X)

#### Introduction (4.2.X.1)
- WebTransport is a framework enabling web clients (browsers) to communicate with servers over secure, multiplexed transport
- Positioned between WebSocket (limited to single ordered reliable TCP stream) and WebRTC DataChannel (P2P-oriented)
- Runs over HTTP/3 at high level
- Dual nature: both transport protocol (IETF) and Web API (W3C)
- Protocol stack includes HTTP3Transport mapping layer for feature negotiation, Extended CONNECT initiation, and datagram/stream mapping
- W3C API published as working draft; IETF standardization expected in 2026

#### Features (4.2.X.2)
- Session-based communication model under Web security model
- Supports multiple independent bidirectional and unidirectional streams
- Supports datagrams (unreliable, message-oriented delivery)
- All traffic multiplexed within same connection over HTTP/3
- Safely exposed to browser applications
- Dual specification: protocol level (IETF) and API level (W3C)
- HTTP/2 mapping available for environments without UDP/QUIC support

#### Benefits (4.2.X.3)
- **Application-level abstraction:** Web-compatible framework and API beyond raw QUIC transport
- **Mixed traffic support:** Combines reliable and low-latency traffic in single logical connection
- **Web security integration:** Origin-based access control, secure contexts, safe for untrusted applications
- **HTTP integration:** Mappings over HTTP/3 and HTTP/2 enable operation where UDP/QUIC unavailable
- **Modern browser API:** W3C API provides high-level JavaScript interface aligned with Web Streams paradigm
- **Alternative to WebSockets:** Native multiplexing and unreliable datagram support

#### Limitations (4.2.X.4)
- **Client-server only:** Primarily for client-server interactions; no standardized NAT traversal like WebRTC
- **Security constraints:** Limited to secure contexts (HTTPS); intentionally restricted low-level transport control
- **Maturity concerns:** W3C API still Working Draft; variable browser support
- **HTTP/2 mapping differences:** HTTP/2 fallback provides "many capabilities" but not identical transport properties to HTTP/3 version

#### Current Applications (4.2.X.5)
- **Client implementations:** Google Chrome and Microsoft Edge browsers support W3C WebTransport API over QUIC
- **Server implementations:**
  - quiche (Rust): https://github.com/cloudflare/quiche
  - aioquic (Python): https://github.com/aiortc/aioquic (experimental support)

## Overall Assessment
This CR provides comprehensive documentation of WebTransport as a candidate protocol for QUIC-based real-time communication services, covering its technical characteristics, advantages for web-based RTC applications, deployment constraints, and current implementation status.