Multi-Path QUIC Proxying UDP in HTTP

Description

MPQUIC-UDP is a protocol framework introduced in 3GPP Release 19 that leverages Multi-Path QUIC (MPQUIC) to proxy User Datagram Protocol (UDP) traffic over HTTP. It is specified in 3GPP TS 24.193 and TS 29.244, which define the protocol aspects and the packet forwarding control protocol (PFCP) extensions, respectively. The core idea is to encapsulate UDP datagrams within HTTP/3 streams carried over QUIC connections, enabling the use of multiple network paths simultaneously. This allows applications that rely on UDP—such as real-time media, online gaming, and IoT telemetry—to benefit from improved reliability, seamless mobility, and bandwidth aggregation without requiring changes to the applications themselves.

The architecture of MPQUIC-UDP involves a client-side proxy and a server-side proxy. The client proxy intercepts UDP packets from the application and encapsulates them into HTTP/3 datagrams or streams, which are then transmitted over one or more QUIC connections. The server proxy decapsulates the HTTP/3 payload back into UDP packets and forwards them to the destination server. This proxying function can be integrated into the User Plane Function (UPF) in the 5G core network, allowing the network to manage and optimize the UDP flows. The use of QUIC provides built-in encryption, congestion control, and multiplexing, while Multi-Path QUIC adds the ability to use multiple access networks (e.g., Wi-Fi and 5G) concurrently.

Key components include the MPQUIC-UDP client and server functions, the HTTP/3 datagram framing, and the PFCP extensions for controlling the proxying behavior in the UPF. The client function is responsible for path management, scheduling UDP packets across available paths, and handling retransmissions if needed. The server function reassembles the UDP packets and ensures in-order delivery if required by the application. The PFCP extensions allow the Session Management Function (SMF) to instruct the UPF to apply MPQUIC-UDP proxying for specific PDU sessions, including parameters such as path selection policies and quality of service (QoS) requirements.

In the network, MPQUIC-UDP plays a crucial role in enhancing the performance of UDP-based services in scenarios where network conditions are challenging, such as in mobility or multi-access environments. By proxying UDP over HTTP/3, it enables the use of web-based infrastructure and security mechanisms, while the multi-path capability ensures that if one path degrades, traffic can be seamlessly shifted to another. This is particularly beneficial for ultra-reliable low-latency communication (URLLC) and enhanced mobile broadband (eMBB) services. The protocol also supports network slicing by allowing different slices to use different paths or QoS policies.

Overall, MPQUIC-UDP represents a significant step in integrating modern transport protocols into 3GPP networks, providing a standardized way to improve UDP transport reliability and flexibility. It aligns with the broader trend of using HTTP/3 and QUIC in telecommunications to simplify and secure data transport.

Purpose & Motivation

MPQUIC-UDP was created to address the limitations of traditional UDP transport in mobile networks, which lacks reliability, congestion control, and multi-path support. UDP is widely used for real-time applications, but its best-effort nature can lead to packet loss and poor performance, especially in mobile environments with varying radio conditions. Existing solutions like QUIC provide reliability and security for HTTP traffic, but UDP applications cannot directly benefit without modification. MPQUIC-UDP bridges this gap by proxying UDP over HTTP/3, allowing UDP applications to leverage QUIC's advanced features without any changes to the applications themselves.

The motivation also stems from the need for seamless mobility and multi-access support in 5G and beyond. With the proliferation of devices that can connect via multiple access technologies (e.g., 5G, Wi-Fi, satellite), there is a desire to aggregate bandwidth and improve reliability by using multiple paths simultaneously. Multi-Path QUIC provides this capability, but its application to UDP traffic required a standardized proxying mechanism. 3GPP Release 19 introduced MPQUIC-UDP to define how this proxying should work within the 5G core network, ensuring interoperability and efficient resource usage.

Furthermore, MPQUIC-UDP enables network operators to apply QoS and policy control to UDP flows more effectively. By terminating the QUIC connections at the UPF, operators can inspect and manage the traffic, apply traffic steering, and enforce security policies. This is particularly important for enterprise and mission-critical services where UDP is prevalent. The specification in TS 24.193 and TS 29.244 ensures that the proxying function can be controlled via the PFCP protocol, integrating it into the existing 5G core architecture.