]> Ericsson

marcus.ihlar@ericsson.com

Ericsson

mirja.kuehlewind@ericsson.com

Nokia

zaheduzzaman.sarker@nokia.com

Web and Internet Transport Standard Communication with Network Elements media bitrate This document specifies a new Capsule (RFC9297) that can be used with CONNECT-UDP (RFC9298), CONNECT-IP (RFC9484), or other future CONNECT extensions to signal throughput advice for traffic that is proxied through an HTTP server. About This Document Status information for this document may be found at . Discussion of this document takes place on the Standard Communication with Network Elements Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction This document specifies an HTTP Capsule (RFC9297) that can be used with CONNECT-UDP (RFC9298), CONNECT-IP (RFC9484), or other future CONNECT extensions to signal throughput advice for traffic proxied through an HTTP server. The extension can be used with the HTTP CONNECT method when the :protocol pseudo-header is equal to "connect-udp" or "connect-ip", as well as with future CONNECT protocols that use the Capsule Protocol.

Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Indicating Support for Throughput Advice Signaling A client that wishes to receive throughput advice capsules can indicate support by sending a request header with the boolean-valued Item Structured Field: "Throughput-Advice: ?1". The HTTP proxy can indicate support by sending a response header with the same boolean-valued Item Structured Field: "Throughput-Advice: ?1". See for information about the boolean format. Once support has been established, a proxy MAY send THROUGHPUT_ADVICE capsules at any time during the lifetime of the stream that originated the request.

THROUGHPUT_ADVICE Capsule Type Format The THROUGHPUT_ADVICE Capsule has the following format: The capsule has the following fields: Direction: Indicates the traffic direction to which this throughput advice applies. Valid values are:

• 0x00: Both uplink and downlink
• 0x01: Uplink (client to target)
• 0x02: Downlink (target to client)

A client MUST treat any other value as a malformed capsule. Rate Limit: The maximum sustainable throughput that the client can expect for proxied traffic, expressed in kilobits per second. Average Window: Indicates the duration over which the bitrate is enforced, expressed in milliseconds. If this field is omitted the average window is assumed to be 67 seconds as described in .

Relationship to the SCONE Protocol This document reuses the SCONE conceptual model for throughput advice but scopes signaling to the HTTP tunnel between a MASQUE client and a MASQUE server. When the Throughput-Advice header is successfully negotiated, the MASQUE server is the entity that originates THROUGHPUT_ADVICE capsules toward the client; the client does not send capsules unless specified by future extensions. Implementations that negotiate Throughput-Advice for a MASQUE tunnel SHOULD NOT initiate or forward SCONE packets on the outer MASQUE connection for the purpose of conveying throughput advice. When a MASQUE proxy observes SCONE packets that belong to an end-to-end inner flow carried by the tunnel, the proxy MUST forward those packets unmodified.

Interaction with QUIC-Aware Forwarding When used in combination with QUIC-Aware Forwarding , QUIC long-header packets are tunnelled rather than being forwarded forwarded directly. Since SCONE packets use a dedicated QUIC version and the long-header format, they will be encapsulated automatically inside the MASQUE tunnel.

Applicability A proxy that intends to rate limit proxied traffic can notify clients using the THROUGHPUT_ADVICE capsule. Reasons for rate limiting traffic through a proxy include enforcement of access network policies, proxy resource management and proxy service differentiation. If the sole purpose of the communication between a client endpoint and a network element is the exchange of throughput advice, it is RECOMMENDED to use more lightweight approaches than HTTP proxying, such as .

Applicability to Proxied Applications In most MASQUE deployments, the client that terminates the HTTP tunnel is not the ultimate endpoint of the application traffic. Throughput advice therefore applies to the aggregate traffic carried by the tunnel rather than to any individual application flow. How a MASQUE client exposes throughput advice to the applications that use the tunnel is out of scope for this document. Implementations may, for example:

• Use the advice to apply back-pressure on proxied traffic;
• Forward the information through an out-of-band API or control channel; or
• Adjust sending behavior on behalf of the application.

For CONNECT-UDP requests, the advice typically corresponds to the throughput of a single proxied flow, whereas for CONNECT-IP requests it applies to the aggregate traffic within the tunnel.

Security Considerations Throughput advice influences application sending behavior and can therefore affect performance and user experience. Implementations MUST treat such signals as advisory information. A malicious or misconfigured proxy could advertise unrealistically low rate limits to degrade service quality or influence path selection and traffic distribution. Clients MAY ignore any received advice. When QUIC-Aware Forwarding is in use, SCONE packets are encapsulated as QUIC long-header packets and therefore not visible to on-path observers. This encapsulation is RECOMMENDED since it prevents correlation between throughput-advice signaling and proxied application traffic.

IANA Considerations

Capsule types This document adds following entries to the "HTTP Capsule Types" registry: New Capsule Type to register

Capsule Type	Value	Specification
THROUGHPUT_ADVICE	TBD	(This document)

HTTP headers This document adds following entry to the "Hypertext Transfer Protocol (HTTP) Field Name Registry": HTTP Field Name to register

Field Name	Template	Status	Reference	Comments
Throughput-Advice		permanent	(This document)

Normative References Mozilla Private Octopus Inc. Fastly Meta Ericsson This document describes a protocol where on-path network elements can give endpoints their perspective on what the maximum achievable throughput might be for QUIC flows. Apple Inc. Apple Inc. Google LLC This document extends UDP Proxying over HTTP to add optimizations for proxied QUIC connections. Specifically, it allows a proxy to reuse UDP 4-tuples for multiple proxied connections, and adds a mode of proxying in which QUIC short header packets can be forwarded and transformed through a HTTP/3 proxy rather than being fully re- encapsulated and re-encrypted. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document describes a set of data types and associated algorithms that are intended to make it easier and safer to define and handle HTTP header and trailer fields, known as "Structured Fields", "Structured Headers", or "Structured Trailers". It is intended for use by specifications of new HTTP fields that wish to use a common syntax that is more restrictive than traditional HTTP field values.

Acknowledgments Zaheduzzaman Sarker have provided significant comments and feedback that has helped shape the draft.