# Summary of S4-260242: RTP over QUIC Media Delivery Protocol for Real-time Communication

## Document Overview

This contribution to TR 26.836 v0.0.1 documents RTP over QUIC (RoQ) as a media delivery protocol for real-time communication services. The document is submitted by InterDigital to the Study on QUIC-based media delivery for real-time communication and services.

## Main Technical Contributions

### References Added

The contribution adds two key normative references:
- **IETF RFC 9221**: "An Unreliable Datagram Extension to QUIC"
- **IETF Draft draft-ietf-avtcore-rtp-over-quic-14**: "RTP over QUIC (RoQ)" (Work in progress)

### Introduction to RTP over QUIC (Section 4.2.X.1)

The contribution introduces RoQ as a framework for transporting RTP and RTCP data over QUIC protocol, providing:
- A minimal and flexible mapping allowing existing RTP-based applications to operate over QUIC instead of UDP
- Leveraging QUIC's built-in features: mandatory encryption, connection migration, multiplexing, and standardized congestion control
- Support for both QUIC streams and QUIC datagrams for encapsulation
- Transport-level feedback that can complement or replace traditional RTCP features

### Features (Section 4.2.X.2)

#### Security and Encapsulation (4.2.X.2.1)
- **Built-in encryption**: TLS 1.3 integrated, eliminating need for separate DTLS layer
- **Dual encapsulation models**:
  - **QUIC STREAM frames**: Reliable, ordered, flow-controlled delivery with potential head-of-line blocking
  - **QUIC DATAGRAM frames**: Unreliable, out-of-order delivery similar to traditional RTP, avoiding head-of-line blocking
- **Flexibility**: Single QUIC connection can carry both encapsulation types simultaneously
- **HoL blocking mitigation**: RoQ senders can open new QUIC streams for different RTP packets using the same flow identifier

#### Multiplexing (4.2.X.2.2)
- Multiple media streams, control streams, and application flows over one QUIC connection
- Application-level flow identifiers for demultiplexing (replacing separate UDP port numbers)
- Simplified NAT/firewall traversal and reduced port usage

#### RTP Packet Handling (4.2.X.2.3)
- RTP packets carried as QUIC payload in STREAM or DATAGRAM frames
- **DATAGRAM considerations**: No internal fragmentation; must respect max_datagram_frame_size and Path MTU
- **STREAM capabilities**: Packet queuing, segmentation, and cancellation mechanisms using STOP_SENDING and RESET_STREAM frames

#### RTCP Packet Handling (4.2.X.2.4)
- RTCP packets carried via QUIC streams or DATAGRAMs
- Mixed operation possible based on application requirements
- **QUIC-to-RTCP mapping**:
  - QUIC loss/acknowledgment patterns can substitute for RTCP NACKs
  - QUIC ECN support can replace RTCP ECN feedback reports
  - CONNECTION_CLOSE frame with Reason Phrase can replace RTCP BYE

### Benefits (Section 4.2.X.3)

1. **Integrated security**: Built-in TLS 1.3 encryption without separate DTLS layer
2. **Simplified connectivity**: Multiplexing over single connection improves NAT/firewall traversal
3. **Standardized congestion control**: Direct use or adaptation of QUIC mechanisms
4. **Reduced RTCP overhead**: Leveraging QUIC's internal metrics (RTT, loss, delivery rates)
5. **Enhanced mobility**: Connection migration support and better NAT traversal for mobile/multi-network clients

### Limitations (Section 4.2.X.4)

1. **Implementation complexity**: More complex than UDP, requiring handling of QUIC connection setup, TLS, and frame semantics
2. **Head-of-line blocking risk**: When using reliable QUIC STREAMs, requires careful design with DATAGRAMs or stream segmentation
3. **Congestion control coordination**: Need to avoid conflicts between RTP and QUIC congestion control algorithms
4. **Deployment maturity**: Limited support in existing media servers, middleboxes, and network devices compared to UDP/DTLS RTP

### Current Applications (Section 4.2.X.5)

The contribution lists three open-source implementations:
1. RTP over QUIC implementation in Go (github.com/mengelbart/roq)
2. RTP-over-QUIC elements for GStreamer (github.com/bbc/gst-roq)
3. Meetecho's open source QUIC library for multimedia applications supporting RoQ and MoQ (github.com/meetecho/imquic)

## Document Type

This is a text proposal contribution adding a new subsection to the technical report, documenting RoQ protocol characteristics for consideration in the QUIC-based media delivery study.