APIs To Expose SCONE Metadata to Applications
draft-eddy-scone-api-02

SCONE                                                            W. Eddy
Internet-Draft                                                 A. Tiwari
Intended status: Informational                               A. Frindell
Expires: 7 May 2026                                                 Meta
                                                         3 November 2025

             APIs To Expose SCONE Metadata to Applications
                        draft-eddy-scone-api-02

Abstract

   This document describes API considerations to provide applications
   with network-supplied information about acceptable network flow
   rates.  Since this information is expected to be signalled from the
   network within the stack below the application using SCONE protocol
   signalling, it needs to be made accessible to applications in order
   for them to pick proper video rates, or to otherwise confine the
   application behavior within network-defined limits.

Status of This Memo

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   This Internet-Draft will expire on 7 May 2026.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  SCONE Background and Introduction . . . . . . . . . . . . . .   2
     1.1.  SCONE API Motivations . . . . . . . . . . . . . . . . . .   4
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   5
   3.  Application Stack Designs . . . . . . . . . . . . . . . . . .   5
   4.  Potential SCONE Metadata Provided By An API . . . . . . . . .   6
   5.  Potential Browser API Extensions  . . . . . . . . . . . . . .   6
     5.1.  Potential Network Information API Inclusion . . . . . . .   7
     5.2.  Potential WebTrans API Inclusion  . . . . . . . . . . . .   8
     5.3.  Potential HLS/DASH Support  . . . . . . . . . . . . . . .   9
     5.4.  Other JavaScript API Options  . . . . . . . . . . . . . .   9
   6.  Potential QUIC API Inclusion  . . . . . . . . . . . . . . . .   9
     6.1.  Potential MoQ API Extension . . . . . . . . . . . . . . .  10
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   9.  Editor's Notes  . . . . . . . . . . . . . . . . . . . . . . .  11
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     10.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  SCONE Background and Introduction

   Video traffic is already 70% of all traffic on the Internet and is
   expected to grow to 80% by 2028.  New formats like short form videos
   have seen tremendous growth in recent years.  Both in developed and
   emerging markets video traffic forms 50-80% of traffic on mobile
   networks.  These growth trends are likely to increase with new
   populations coming online on mobile-first markets and the observation
   that unlike text content, video content consumption is not being
   limited by literacy barriers.  On the other hand, the electromagnetic
   spectrum is a limited resource.  In order to ensure that mobile
   networks continue functioning in a healthy state despite this
   incredible growth, communication service providers (CSPs) will be
   required to make infrastructure investments such as more licensed
   spectrum, cell densification, massive MIMO etc.  In order to flatten
   the rate of growth, CSPs in several markets attempt to identify and

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   throttle video traffic based on user data plans.  There are several
   problems with this kind of throttling:

   1.  CSPs can not explicitly measure the effect that throttling has on
       the end user’s quality of experience (QoE) making this an open
       loop approach.

   2.  Traffic detection and throttling for every flow is compute
       intensive for CSPs.  With distributed UPF (user plane function)
       in 5G mobile networks more nodes in CSP network may need to
       support traffic detection and throttling.  Traffic detection can
       have inaccuracies and these inaccuracies are expected to increase
       as the content delivery industry moves towards end-2-end
       encryption like TLS 1.3 and encrypted client hello (ECH).

   3.  The unpredictable and non-transparent behavior of traffic
       throttlers used by CSPs confuse the bandwidth estimation and
       congestion control protocols being used within end-2-end video
       delivery sessions between content server and client.  This
       results in poor quality of experience (QoE) for the end user.

   4.  Content and Application Providers (CAPs) are designing algorithms
       to detect the presence of such traffic throttlers to counter
       their detrimental effects.  These algorithms have their own
       inaccuracies in detection and add compute resources on the CAP
       side.

   An alternative approach is for CAPs to self-adapt the traffic
   corresponding to video flows.  Since CAPs control the client and
   server endpoints and can measure end user QoE, they are in a better
   position to do this self-adaptation in a close loop manner.  This
   alternative approach has already been proven to improve user QoE in
   production deployments [YouTube].

   For this alternative approach to work a standardized secure on-path
   network interface is required which will enable CSP controlled
   network elements to signal the desired traffic profile
   characteristics to the CAP client/server endpoints.  The Standard
   Communication with Network Elements (SCONE) protocol (previously
   known as SADCDN and SCONEPRO) is an IETF working group motivated by
   this alternate approach.

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1.1.  SCONE API Motivations

   The general problem statement for SCONE is described in the video
   optimization requirements document
   [I-D.joras-scone-video-optimization-requirements], including the
   shaping or throttling that CSPs perform.  While this problem
   currently has especially large impact on a few large content
   providers, solutions for SCONE are generally applicable to any
   applications that use QUIC [RFC9000] and are subject to throttling
   within CSP networks.

   General use of SCONE metadata for any applications can be facilitated
   via an open Application Programming Interface (API) that could be
   implemented in appropriate QUIC stacks, web browsers, or other
   libraries.

   There are two aspects to consider for an API:

   1.  How will applications learn about network information that is
       discovered by SCONE lower in the stack?  This is a primary
       consideration in this document.

   2.  How will applications signal their type (e.g. video streaming) or
       other relevant properties to the stack, to indicate that they are
       SCONE-capable?  This is a secondary consideration in this
       document, because currently networks that perform throttling have
       built-in methods to implicitly determine the appropriate flows to
       throttle.

   The SCONE metadata may be available at different places in the
   protocol stack implementation spanning operating system, QUIC
   library, browser, and application code.  This document tries to
   initially make no assumptions about how the SCONE signalling works,
   and so considers possibilities to integrate the metadata into APIs
   provided from OSes, QUIC libraries, web browsers, etc.  There are
   open questions at the moment about SCONE signaling via on-path
   devices, what type of information is conveyed, and how it is
   represented.  The API capabilities may be limited by the protocol
   decisions, and realistic concerns about signaling across network
   domain boundaries, etc.

   During early SCONE discussions, there have been suggestions that the
   API might take inspiration from Explicit Congestion Notification
   (ECN), as ECN also exposes information from the network (congestion
   experienced codepoints) to end hosts, and the design contends with
   potential for abuse, crosses network domain boundaries, and has other
   desirable properties.  Some key differences from ECN in usage
   relavent to a SCONE API have been pointed out:

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   1) ECN information is consumed either by transport protocols (e.g.
   TCP, MPTCP, and SCTP) or congestion control algorithms operating
   above e.g. UDP or UDP-Lite [RFC8303] [RFC8304], but typically below
   an application.  For instance, within QUIC stacks used for video
   streaming, ECN can be consumed by the QUIC congestion control, but is
   not exposed to the application.

   2) The exposure of SCONE metadata is intended to be at the level of
   data flows (e.g. to aid application decisions about what media
   quality to fetch), whereas ECN is consumed at the level of packets
   (within an individual flow).

   While ECN is not a solution for SCONE [I-D.tomar-scone-ecn], it is
   productive to consider as an example based on similarities,
   including:

   *  Signaling is coming from the network, and may cross different
      network domains.

   *  Signaling points can also drop packets, and the signaling
      participation is indtended to avoid excessive packet drops.

   The purpose of this document is only to demonstrate that general API
   exposure of the SCONE metadata is achievable without prescribing a
   specific API solution.  It is envisioned that one or more specific
   API solutions will be defined either through IETF or W3C, to
   correspond with the SCONE protocol specification.  At least in its
   current form, this document is not intended to be published as an
   RFC.

2.  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 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Application Stack Designs

   There are a variety of different application stack designs that are
   relevant.  The main assumption for SCONE in general is that QUIC is
   used.

   Applications could, for instance, (1) include their own QUIC
   implementation, (2) use QUIC directly through a linked software
   library, or (3) run within a web browser, using QUIC more indirectly
   via browser APIs.

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   The SCONE working group is defining the signalling protocol
   [I-D.ietf-scone-protocol]).  as part of the QUIC stack, with the
   information inserted by an on-path SCONE network element.

   Other approaches that do not seem to be as actively pursued at the
   moment are: (1) signaling via other IP or transport methods below
   QUIC (e.g. IP extension headers, UDP options, etc.) that might be
   inserted on the path, and (2) signaling via the OS, with the
   information coming in network advertisements separate from the
   transport connection (e.g. via Router Advertisements or DHCP).
   Therefore, OS-provided APIs and socket API extensions are not
   considered further in this document, since signaling is assumed to be
   implemented using QUIC.

   It is important to note that QUIC library APIs are not standardized;
   they differ between common QUIC libraries, and so this document only
   suggests in a general sense of how the QUIC stack should convey this
   information to applications.

4.  Potential SCONE Metadata Provided By An API

   SCONE is chartered to provide "throughput advice".  The SCONE
   protocol encodes the rate signal in a QUIC packet field that may be
   periodically updated.  The protocol [I-D.ietf-scone-protocol]
   currently discusses the expectations on lifetime or validity time of
   the rate signals and update behavior.

   The remainder of this document considers API extensions in general to
   provide SCONE data, whether it be a single data rate, or more
   comprehensive characterization.

5.  Potential Browser API Extensions

   For browser applications, there are multiple different browser APIs
   that might be extended to include SCONE metadata; notably including:

   *  W3C Network Information

   *  WebTransport using QUIC

   *  HTTP Live Streaming (HLS) or Dynamic Adaptive Streaming over HTTP
      (DASH) client libraries

   *  Any Javascript HTTP requests that directly or indirectly use
      HTTP/3.

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   In either of these cases, the corresponding W3C API definitions are
   the proper place for actual definition of API extensions, and this
   document is merely exploring possibilities.

   The exploration is primarily around the ability to convey SCONE
   signaling information that is discovered from the network path up to
   applications.  In addition, to indicate an application's desire to
   use SCONE signaling in the first place, some small API extension is
   also be required, unless relying totally on the underlying stack or
   network to infer which flows should be receiving SCONE treatment
   (e.g. as networks already infer which flows to throttle).

5.1.  Potential Network Information API Inclusion

   The W3C Network Information API [W3C-NetInfo] is supported to some
   extent by several, but not all, common web browsers today.  It
   provides the possibility for an appliction to determine what
   underlying connection types or "effective" connection types (e.g.
   cellular. bluetooth, etc.) may be in use, with a corresponding set of
   performance parameter estimates including:

   *  Round Trip Time (RTT) in milliseconds providing a delay estimate.

   *  downlink in megabits per second providing an effective bandwidth
      estimate based on recently observed application layer throughput
      or properties of the underlying connectivity technology.

   *  downlinkMax in megabits per second representing an upper bound on
      the downlink speed of the first network hop, based on the
      underlying connectivity technology.

   The downlink and downlinkMax could be leveraged as places to put the
   SCONE-discovered rate limit for an application, since anything
   greater than the SCONE-discovered rate would not be expected to be
   usable for the application.

   Alternatively, another field could be added to the NetworkInformation
   interface in order to specifically provide the SCONE metadata.

   In any case, a good property of the Network Information API is that
   an application can hook event handlers to be notified of changes, so
   that if there are limits that kick-in or are lifted midway into an
   application's lifetime (e.g. due to some mobility, etc.), the
   application will be able to be easily notified and adapt.

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5.2.  Potential WebTrans API Inclusion

   In the future, WebTransport (WEBTRANS) might be used by SCONE's
   targeted types of applications, such as browser-based adaptive
   streaming.  The IETF WEBTRANS working group is liasing with W3C as
   the IETF defines the protocol specification, whereas the W3C defines
   the API to use it.  This case is similar to the IETF RTCWEB and W3C
   WebRTC WG coordination in the past.  The same model of collaboration
   between IETF and W3C should work for SCONE metadata, and the
   information provided could be discussed with the WEBTRANS WG in the
   IETF and notified to the W3C later, either through common
   participation and/or formal liason statement.

   The existing WebTrans API definition from W3C includes a "getStats()"
   method, that is defned in order to asynchronously gather and report
   statistics for a WebTransport underlying connection.  It returns a
   WebTransportConnectionStats object that is defined as a dictionary,
   including a number of items such as:

   *  bytesSent

   *  packetsSent

   *  bytesLost

   *  packetsLost

   *  bytesReceived

   *  packetsReceived

   *  smoothedRtt

   *  rttVariation

   *  minRtt

   *  WebTransportDatagramStats datagrams

   *  estimatedSendRate

   The estimatedSendRate is an unsigned long long, in bits per second,
   calculated by the congestion control algorithm in the user agent.
   This would be in the "upstream" direction to a CSP, though, rather
   than the "downstream" from a CSP, so is not useful to a client
   application in receiving indication of a downstream throttling rate
   from the network.

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   Since other measurements are already included and the
   WebTransportConnectionStats is a dictionary, it seems natural to
   extend it to include additional optional fields, such as an allowed
   media rate, or other types of fields providing the application
   information that the underlying host or stack have discovered about
   the presence of throttling or explicit signaling of allowed media
   rate on a path.

   Such extensions might be including at a "MAY" level of conformance
   statement (rather than "SHALL" as used by all of the currently-
   defined information elements), as the allowed media rate will not be
   universally present or even useful for all WebTransport applications.
   Alternatively, it could be set to a "null" value similar to how the
   estimatedSendRate is sent when it is unknown by the user agent.

5.3.  Potential HLS/DASH Support

   Client libraries for HLS and DASH will use the underlying Javascript
   APIs or other underlying APIs, and might rely on them for SCONE
   metadata support, as discussed in the next subsection.

5.4.  Other JavaScript API Options

   Typical HTTP adaptive streaming applications using existing browser
   API options would be ideal to support as directly as possible.  There
   are different ways to transfer HTTP/3 data provided to JavaScript
   applications that might be applicable.

   For instance, things like jQuery.ajax() or the "Fetch" API may be
   used.  In this case, there is little or no information about the
   network path state provided, though there are either jqXHR or
   Response objects returned that (for instance) allow HTTP headers to
   be conveyed, and in both cases could be extended to include SCONE
   metadata.  These are returned at the completion of the HTTP transfer,
   however.  It might be more difficult to support more dynamic updates
   such as providing the metadata to an application mid-transfer so that
   an application might quickly switch to other media rates for future
   video segments being pre-fetched.

6.  Potential QUIC API Inclusion

   While there are no standard QUIC APIs, and there are multiple
   different styles in use, many QUIC implementations include objects in
   the API that represent the QUIC connections directly, and allow
   setting callbacks for connection-related events, or allow direct
   querying of connection state.  SCONE metadata could either be
   supported as a type of callback event, triggered when the metadata is
   received, or it could be included within other connection state in a

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   polled or interrogated data structure.

   Regarding identification of the application flow type, options for a
   QUIC API may include adding "SCONE-capable" type of flag or an
   optional flow-type tag that can be set by applications.  Compared to
   the complexity of existing QUIC APIs, these could be small additions.

6.1.  Potential MoQ API Extension

   While Media over QUIC (MoQ) is being defined, it is intended for
   media streaming over QUIC, which might be applicable to SCONE, in
   case adaptive rate streams are detected and throttled by CSPs.  As
   yet, there is no standard MoQ API, an MoQ session is currently scoped
   either to a QUIC connection or a WebTransport session, so it should
   not be difficult to expose information learned by either transport
   stack to MoQ applications.  Since MoQ applications are media flows,
   it may be very simple for an application flow type to be conveyed or
   inferred via an eventual MoQ API..

7.  Security Considerations

   General SCONE security considerations are discussed in the other
   documents covering specific network-to-host signaling methods.
   Privacy concerns have also been discussed in
   [I-D.tomar-scone-privacy].

   Existing APIs that expose information about the network path to
   applications have documented security considerations, especially with
   regard to user privacy.  For instance, there may be concerns that
   such information can be used to assist in fingerprinting users,
   defeating anonymization, or otherwise exposing more information about
   the user to the application than the user might explicitly consent
   to.  Such concerns have been document, for example, with regard to
   the Network Information API.

   By providing additional information about throttling rate limits
   within the path, SCONE could increase the amount of information
   availble on top of that provided by the current APIs.  For instance,
   if the rate information is very fine-grained, it could be useful in
   fingerprinting.

   Generally, however, the CSP throttling information is currently very
   coarse grained, as it is used today.  Additionally, the application
   providers authenticate their users, and their is not an expectation
   of anonymity in popular platforms today.

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   Beyond this, it is also the case that information provided by SCONE
   can already be learned by CAP endpoints through various other
   mechanisms (e.g. the effect of on-path throttlers is clearly visible
   by observing application traffic packet flows).  SCONE simply makes
   the signaling explicit, rather than requiring it to be observed and
   inferred separately.

8.  IANA Considerations

   This document has no IANA actions.

9.  Editor's Notes

   This section to be removed prior to any potential publication within
   an RFC.

   *  The "CSP" term is overloaded, especially with regard to web
      technology, and might be changed to "carrier", "network operator",
      etc. in the future, but would need to be consistent with
      terminology in other SCONE documents.

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

   [RFC9000]  Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", RFC 9000,
              DOI 10.17487/RFC9000, May 2021,
              <https://www.rfc-editor.org/rfc/rfc9000>.

10.2.  Informative References

   [I-D.druta-scone-video-session-data-rate]
              Druta, D., Halepovic, E., and T. Karagioules, "Video
              Session Data Rate for SCONE protocol", Work in Progress,
              Internet-Draft, draft-druta-scone-video-session-data-rate-
              00, 30 January 2025,
              <https://datatracker.ietf.org/doc/html/draft-druta-scone-
              video-session-data-rate-00>.

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   [I-D.ietf-scone-protocol]
              Thomson, M., Huitema, C., Oku, K., Joras, M., and L. M.
              Ihlar, "Standard Communication with Network Elements
              (SCONE) Protocol", Work in Progress, Internet-Draft,
              draft-ietf-scone-protocol-03, 20 October 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-scone-
              protocol-03>.

   [I-D.joras-scone-video-optimization-requirements]
              Joras, M., Tomar, A., Tiwari, A., and A. Frindell, "SCONE
              Video Optimization Requirements", Work in Progress,
              Internet-Draft, draft-joras-scone-video-optimization-
              requirements-01, 12 May 2025,
              <https://datatracker.ietf.org/doc/html/draft-joras-scone-
              video-optimization-requirements-01>.

   [I-D.tomar-scone-ecn]
              Tomar, A., Ihlar, L. M., Eddy, W., Swett, I., Tiwari, A.,
              and M. Joras, "SCONE Need for Defining A New On-Path
              Signaling Mechanism", Work in Progress, Internet-Draft,
              draft-tomar-scone-ecn-01, 7 May 2025,
              <https://datatracker.ietf.org/doc/html/draft-tomar-scone-
              ecn-01>.

   [I-D.tomar-scone-privacy]
              Tomar, A., Eddy, W., Tiwari, A., and M. Joras, "SCONE
              Privacy Properties and Incentives for Abuse", Work in
              Progress, Internet-Draft, draft-tomar-scone-privacy-01, 7
              May 2025, <https://datatracker.ietf.org/doc/html/draft-
              tomar-scone-privacy-01>.

   [RFC8303]  Welzl, M., Tuexen, M., and N. Khademi, "On the Usage of
              Transport Features Provided by IETF Transport Protocols",
              RFC 8303, DOI 10.17487/RFC8303, February 2018,
              <https://www.rfc-editor.org/rfc/rfc8303>.

   [RFC8304]  Fairhurst, G. and T. Jones, "Transport Features of the
              User Datagram Protocol (UDP) and Lightweight UDP (UDP-
              Lite)", RFC 8304, DOI 10.17487/RFC8304, February 2018,
              <https://www.rfc-editor.org/rfc/rfc8304>.

   [W3C-NetInfo]
              W3C, "The Network Information API", 11 May 2020,
              <https://wicg.github.io/netinfo/>.

   [YouTube]  YouTube, "YouTube Plan Aware Streaming", 21 March 2024,
              <https://datatracker.ietf.org/meeting/119/materials/
              slides-119-sconepro-youtube-plan-aware-streaming-01>.

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Acknowledgments

   This document represents collaboration and inputs from others,
   including:

   *  Anoop Tomar

   *  Matt Joras

   *  Bryan Tan

   Additional, helpful critique and comments were provided by:

   *  Lucas Pardue

   *  Ted Hardie

   *  Michael Welzl

   *  Gorry Fairhurst

   *  Brian Trammell

Authors' Addresses

   Wesley Eddy
   Meta
   Email: wesleyeddy@meta.com

   Abhishek Tiwari
   Meta
   Email: atiwari@meta.com

   Alan Frindell
   Meta
   Email: afrind@meta.com

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