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Transport MASQUE Internet-Draft Application protocols using the QUIC transport protocol rely on streams, and optionally the DATAGRAM extension, to carry application data. Streams and datagrams can be multiplexed but QUIC provides no interoperable prioritization scheme or signaling mechanism itself. The HTTP Extensible Prioritization scheme describes how to prioritize streams in HTTP/2 and HTTP/3. This document adopts the scheme to support HTTP datagrams. Note tho Readers RFC EDITOR: please remove this section before publication Source code and issues list for this draft can be found at https://github.com/LPardue/draft-pardue-masque-dgram-priority.

Introduction Application protocols using the QUIC transport protocol rely on streams, and optionally the DATAGRAM extension , to carry application data. Streams and datagrams can be multiplexed but QUIC provides no interoperable prioritization scheme or signaling mechanism itself. The HTTP Extensible Prioritization scheme describes how to prioritize streams in HTTP/2 and HTTP/3. This document adopts the scheme to support HTTP datagrams . The Extensible Priorities scheme for HTTP describes how clients can send priority signals related to requests in order to suggest how a server allocates resources to serving responses. When the protocol is HTTP/2, responses are carried on streams. When the protocol is HTTP/3, responses are carries on QUIC streams. While QUIC streams support multiplexing natively via use of a stream identifier, the QUIC DATAGRAM extension does not provide any such identifier. HTTP datagrams supports multiplexing using a set of application-level identifiers that can be controlled and accessed by HTTP/3. One identifer relates to a request stream, the second, optional, identifer relates to an abstract context. does not, however, define any means for multiplexed datagram prioritization. When the application protocol is HTTP/3, HTTP Datagrams can map directly to QUIC datagrams or they can be carried on streams using a DATAGRAM Capsule; see . This document describes how the Extensible Priorities scheme applies to HTTP datagrams. Priority signals sent by clients, related to requests, can also be considered input to server scheduling decisions for HTTP datagrams mapped to QUIC datagrams.

Notational Conventions 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. The term sf-integer is imported from .

Signalling Datagram Priority The Extensible Prioritization scheme provides a framework for communicating and acting upon priority parameters, using formats. It defines the urgency and incremental parameters and provides guidance to implementers about how to act on these parameters, in combination with other inputs, to make resource allocation and scheduling choices. Urgency communicates the client-view of request importance, and incremental communicates how the client intends to process response data as it arrives. Parameters are communicated in HTTP headers or version-specific frames. A client omitting the urgency or incremental parameters can be interpreted by the server as a signal to apply default priorities. The core scheme is extensible, new parameters can be defined to augment the base ones. This specification defines the datagram-urgency (du) extension parameter that operates in addition to the base urgency. There is no extension to the base incremental behavior; individual datragrams, even if belonging to the same identifier, are messages that are expected to be processed individually as they arrive.

Datagram Urgency The datagram-urgency parameter (du) takes an integer between 0 and 7, in descending order of priority. This range matches the base urgency (u) parameter range; see Section 4.1 of . The value is encoded as an sf-integer. There is no default value. This parameter indicates the sender's recommendation, based on the expectation that the server would transmit HTTP datagrams in the order of their datagram-urgency values if possible. The smaller the value, the higher the precedence. Omitting the datagram-urgency parameter is a signal to apply the value of the urgency parameter. The following example shows a request for a CSS file with the urgency set to 0, any associated datagrams have the lower urgency of 2: Endpoints MUST NOT treat reception of the datagram-urgency parameter, even if HTTP datagram support is not enabled. The datagram-urgency parameter applies only to HTTP datagrams mapped to QUIC datagrams. Datagram capsules are sent on streams, so the base urgency parameter applies to them.

Prioritization of Contexts The datagram-urgency parameter applies to all HTTP datagram contexts related to a request stream. Prioritization of individual contexts is not supported.

Reprioritization Reprioritization is supported using the existing mechanisms defined in Section 6 of .

Client Scheduling Clients MAY use datagram-urgency to make local processing or scheduling choices about HTTP datagrams related to the requests it initiates.

Server Scheduling Priority signals are input to a prioritization process. Expressing priority is only a suggestion. The datagram-urgency parameter introduces new scheduling considerations on top of those presented in Section 10 of . It is RECOMMENDED that, when possible, servers send higher urgency HTTP datagrams before lower urgency datagrams. Where streams and datagrams have equal urgency and datagram-urgency, it is RECOMMENDED that servers alternate emitting HTTP datagrams and stream bytes. Where servers implement the recommendations in Section 10 of , alternating between datagram and stream data will result in fair scheduling. This recommendation holds whether stream are incremental or not. It is RECOMMENDED that servers schedule DATAGRAM capsules the same as response data.

Retransmission Scheduling Section 12 of provides guidance about scheduling of retransmission data vs. new data. Since QUIC datagrams are not retransmitted, endpoints that prioritize QUIC stream retransmission data could delay datagrams. Furthermore, since DATAGRAM capsules are sent as stream data, they are subject to retransmission and could also delay native QUIC datagrams.

Security Considerations There are believed to be no additional considerations to those presented in .

IANA Considerations This specification registers the following entry in the HTTP Priority Parameters Registry

Name:

datagram-urgency

Description:

Priority of HTTP datagrams

Reference:

This document

References Normative References Apple Inc. Apple Inc. Google LLC This document defines an extension to the QUIC transport protocol to add support for sending and receiving unreliable datagrams over a QUIC connection. Discussion of this work is encouraged to happen on the QUIC IETF mailing list quic@ietf.org (mailto:quic@ietf.org) or on the GitHub repository which contains the draft: https://github.com/quicwg/ datagram (https://github.com/quicwg/datagram). Fastly Cloudflare This document describes a scheme for prioritizing HTTP responses. This scheme expresses the priority of each HTTP response using absolute values, rather than as a relative relationship between a group of HTTP responses. This document defines the Priority header field for communicating the initial priority in an HTTP version-independent manner, as well as HTTP/2 and HTTP/3 frames for reprioritizing the responses. These share a common format structure that is designed to provide future extensibility. Google LLC Cloudflare The QUIC DATAGRAM extension provides application protocols running over QUIC with a mechanism to send unreliable data while leveraging the security and congestion-control properties of QUIC. However, QUIC DATAGRAM frames do not provide a means to demultiplex application contexts. This document describes how to use QUIC DATAGRAM frames when the application protocol running over QUIC is HTTP/3. It associates datagrams with client-initiated bidirectional streams and defines an optional additional demultiplexing layer. Additionally, this document defines how to convey datagrams over prior versions of HTTP. 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. Informative References This document defines the core of the QUIC transport protocol. QUIC provides applications with flow-controlled streams for structured communication, low-latency connection establishment, and network path migration. QUIC includes security measures that ensure confidentiality, integrity, and availability in a range of deployment circumstances. Accompanying documents describe the integration of TLS for key negotiation, loss detection, and an exemplary congestion control algorithm.

Acknowledgements This document is inspired by discussion by many people across HTTP, QUIC and MASQUE WGs.