Network Working Group                                           J. Arkko
Internet-Draft                                                  Ericsson
Intended status: Informational                          22 February 2021
Expires: 26 August 2021

 Considerations on Information Passed between Networks and Applications


   Path signals are messages seen by on-path elements examining
   transport protocols.  Current preference for good protocol design
   indicates desire for constructing explict rather than implicit
   signals to carry information.  For instance, the ability of various
   middleboxes to read TCP messaging was an implicit signal that lead to
   difficulties in evolving the TCP protocol without breaking
   connectivity through some of those middleboxes.

   This document discusses the types of information that could be passed
   in these path signals, and provides some advice on what types of
   information might be provided in a beneficial manner, and which
   information might be less likely to be revealed or used by
   applications or networks.

Status of This Memo

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   This Internet-Draft will expire on 26 August 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Past Experiences and Guidance . . . . . . . . . . . . . . . .   2
   3.  Principles  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Information Specificity . . . . . . . . . . . . . . . . .   3
     3.2.  Granularity . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Informative References  . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   [RFC8558] discusses the topic of path signals: Path signals are
   messages seen by on-path elements examining transport protocols.
   There's a difference between implicit and explicit signals.  For
   instance, TCP's well-known messages [RFC0793] are in the clear, and
   often interpreted in various ways by on-path elements.  In contrast,
   QUIC protects almost all of this information, and hence end-to-end
   signaling becomes opaque for network elements in between.  QUIC does
   provide some information, but has chosen to make these signals (such
   as the Spin bit) explicit [I-D.ietf-quic-transport].

   Many attempts have been made at network - application collaboration
   using path signals.  Section 2 discusses some of the experiences and
   guidelines determine from those attempts.  This draft then focuses on
   the specific question of what kind of data can be passed.

2.  Past Experiences and Guidance

   Incentives are a well understood problem in general but perhaps not
   fully internalised for various collaborative like designs.  The
   principle is that both receiver and sender of information must
   acquire tangible and immediate benefits from the communication, such
   as improved performance,

   A related issue is understanding whether there is or is not a
   business model or ecosystem change.  Some designs may work well
   without any monetary or payment or cross-administrative domains

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   agreements.  For instance, I could ask my packets to be prioritised
   relative to each other and that shouldn't affect anything else.  Some
   other designs may require a matching business ecosystem change to
   support what is being proposed, and may be much harder to achieve.
   For instance, requesting prioritisation over other people's traffic
   may imply that you have to pay for that which may not be easy even
   for a single provider let alone across many.

   But on to more technical aspects.

   The main guidance in [RFC8558] is to be aware that implicit signals
   will be used whether intended or not.  Protocol designers should
   consider either hiding these signals when the information should not
   be visible, or using explicit signals when it should be.

   [I-D.irtf-panrg-what-not-to-do] discusses many past failure cases, a
   catalogue of past issues to avoid.  It also provides relevant
   guidelines for new work, from discussion of incentives to more
   specific observations, such as the need for outperforming end-to-end
   mechanisms (Section 4.4), considering the need for per-connection
   state (Section 4.6), and so on.

   There are also more general guidance documents, e.g., [RFC5218]
   discusses protocol successes and failures, and provides general
   advice on incremental deployability etc.  Internet Technology
   Adoption and Transition (ITAT) workshop report [RFC7305] is also
   recommended reading on this same general topic.  And [RFC6709]
   discusses protocol extensibility, and provides general advice on the
   importance of global interoperability and so on.

3.  Principles

   This section attempts to provide some further guidelines, relating to
   information that can be passed in path signals.  Hopefully, these
   guidelines can help future designers, explain past issues and
   recommend useful models to apply.

3.1.  Information Specificity

   One common problem in finding a workable solution for network -
   application collaboration is information leakage.  All parties are
   afraid of either their own propietary information or the users' data
   leaking to others.  Oddly enough, no one is usually worried about
   users' data leaking to themselves, but I digress. :-)

   [I-D.per-app-networking-considerations] discusses how applications
   may be identified through collaboration mechanisms.  This can be
   harmful, as in extreme cases it may lead to undesirable

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   prioritization decisions or even blocking certain applications.
   [I-D.per-app-networking-considerations] explains how to reduce the
   latter problem by categories or requested service rather than
   specific application identity, such as providing the category "video
   call service" rather than the name of a particular application
   performing conference call or video call services.  This points to a
   more general principle of information specificity, providing only the
   information that is needed for the other party to perform the
   collaboration task that is desired by this party, and not more.  This
   applies to information sent by an application about itself,
   information sent about users, or information sent by the network.

   An architecture can follow the guideline from RFC 8558 in using
   explicit signals, but still fail to differentiate properly between
   information that should be kept private and information that should
   be shared.

   In looking at what information can or cannot easily be passed, we can
   look at both information from the network to the application, and
   from the application to the network.

   For the application to the network direction, user-identifying
   information can be problematic for privacy and tracking reasons.
   Similarly, application identity can be problematic, if it might form
   the basis for prioritization or discrimination that the that
   application provider may not wish to happen.  It may also have
   undesirable economic consequences, such as extra charges for the
   consumer from a priority service where a regular service would have

   On the other hand, as noted above, information about general classes
   of applications may be desirable to be given by application
   providers, if it enables prioritization that would improve service,
   e.g., differentiation between interactive and non-interactive

   For the network to application direction there's less directly
   sensitive information.  Various network conditions, predictive
   bandwidth and latency capabilities, and so on might be attractive
   information that applications can use to determine, for instance,
   optimal strategies for changing codecs.

   However, care needs to be take to ensure that neither private
   information about the individual user (such as user's physical
   location) is not indirectly exposed through this information.
   Similarly, this information should not form a mechanism to provide a
   side-channel into what other users are doing.

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3.2.  Granularity

   In the IAB Covid-19 Network Impacts workshop Jana Iyengar brought up
   the granularity of operations [I-D.iab-covid19-workshop].  There are
   many reasons why per-flow designs are problematic: scalability, need
   to release information about individual user's individual activities,
   etc.  Perhaps designs that work on aggregates would work better.

4.  Acknowledgments

   The author would like to thank Mirja Kuhlewind, Tommy Pauly, Ted
   Hardie, David Allan, Brian Trammell, Szilvezter Nadas, Zaheduzzaman
   Sarker, Joel Halpern, Magnus Westerlund, Jana Iyengar and Balaz Varga
   for interesting thoughts and proposals in this space.

5.  Informative References

              Arkko, J., Farrell, S., Kuhlewind, M., and C. Perkins,
              "Report from the IAB COVID-19 Network Impacts Workshop
              2020", Internet Draft (Work in Progress), draft-iab-
              covid19-workshop, IETF , February 2021.

              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", Work in Progress, Internet-Draft,
              draft-ietf-quic-transport-34, 14 January 2021,

              Dawkins, S., "Path Aware Networking: Obstacles to
              Deployment (A Bestiary of Roads Not Taken)", Work in
              Progress, Internet-Draft, draft-irtf-panrg-what-not-to-do-
              17, 10 February 2021, <

              Colitti, L. and T. Pauly, "Per-Application Networking
              Considerations", Work in Progress, Internet-Draft, draft-
              per-app-networking-considerations-00, 15 November 2020,

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,

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   [RFC5218]  Thaler, D. and B. Aboba, "What Makes for a Successful
              Protocol?", RFC 5218, DOI 10.17487/RFC5218, July 2008,

   [RFC6709]  Carpenter, B., Aboba, B., Ed., and S. Cheshire, "Design
              Considerations for Protocol Extensions", RFC 6709,
              DOI 10.17487/RFC6709, September 2012,

   [RFC7305]  Lear, E., Ed., "Report from the IAB Workshop on Internet
              Technology Adoption and Transition (ITAT)", RFC 7305,
              DOI 10.17487/RFC7305, July 2014,

   [RFC8558]  Hardie, T., Ed., "Transport Protocol Path Signals",
              RFC 8558, DOI 10.17487/RFC8558, April 2019,

Author's Address

   Jari Arkko


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