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Network Working Group                                           J. ArkkoInternet-Draft                                                  EricssonIntended status: Informational                          22 February 2021Expires: 26 August 2021Considerations on Information Passed between Networks and Applicationsdraft-arkko-path-signals-information-00Abstract   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   This Internet-Draft is submitted in full conformance with the   provisions ofBCP 78 andBCP 79.   Internet-Drafts are working documents of the Internet Engineering   Task Force (IETF).  Note that other groups may also distribute   working documents as Internet-Drafts.  The list of current Internet-   Drafts is athttps://datatracker.ietf.org/drafts/current/.   Internet-Drafts are draft documents valid for a maximum of six months   and may be updated, replaced, or obsoleted by other documents at any   time.  It is inappropriate to use Internet-Drafts as reference   material or to cite them other than as "work in progress."   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.Arkko                    Expires 26 August 2021                 [Page 1]

Internet-Draft              Path Signals Info              February 2021   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document.   Please review these documents carefully, as they describe your rights   and restrictions with respect to this document.  Code Components   extracted from this document must include Simplified BSD License text   as described in Section 4.e of theTrust Legal Provisions and are   provided without warranty as described in the Simplified BSD License.Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .22.  Past Experiences and Guidance . . . . . . . . . . . . . . . .23.  Principles  . . . . . . . . . . . . . . . . . . . . . . . . .33.1.  Information Specificity . . . . . . . . . . . . . . . . .33.2.  Granularity . . . . . . . . . . . . . . . . . . . . . . .54.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .55.  Informative References  . . . . . . . . . . . . . . . . . . .5   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .61.  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 domainsArkko                    Expires 26 August 2021                 [Page 2]

Internet-Draft              Path Signals Info              February 2021   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 undesirableArkko                    Expires 26 August 2021                 [Page 3]

Internet-Draft              Path Signals Info              February 2021   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 fromRFC 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   worked.   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   services.   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.Arkko                    Expires 26 August 2021                 [Page 4]

Internet-Draft              Path Signals Info              February 20213.2.  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   [I-D.iab-covid19-workshop]              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.   [I-D.ietf-quic-transport]              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,              <https://www.ietf.org/archive/id/draft-ietf-quic-transport-34.txt>.   [I-D.irtf-panrg-what-not-to-do]              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, <https://www.ietf.org/archive/id/draft-irtf-panrg-what-not-to-do-17.txt>.   [I-D.per-app-networking-considerations]              Colitti, L. and T. Pauly, "Per-Application Networking              Considerations", Work in Progress, Internet-Draft,draft-per-app-networking-considerations-00, 15 November 2020,              <https://www.ietf.org/archive/id/draft-per-app-networking-considerations-00.txt>.   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,RFC 793, DOI 10.17487/RFC0793, September 1981,              <https://www.rfc-editor.org/info/rfc793>.Arkko                    Expires 26 August 2021                 [Page 5]

Internet-Draft              Path Signals Info              February 2021   [RFC5218]  Thaler, D. and B. Aboba, "What Makes for a Successful              Protocol?",RFC 5218, DOI 10.17487/RFC5218, July 2008,              <https://www.rfc-editor.org/info/rfc5218>.   [RFC6709]  Carpenter, B., Aboba, B., Ed., and S. Cheshire, "Design              Considerations for Protocol Extensions",RFC 6709,              DOI 10.17487/RFC6709, September 2012,              <https://www.rfc-editor.org/info/rfc6709>.   [RFC7305]  Lear, E., Ed., "Report from the IAB Workshop on Internet              Technology Adoption and Transition (ITAT)",RFC 7305,              DOI 10.17487/RFC7305, July 2014,              <https://www.rfc-editor.org/info/rfc7305>.   [RFC8558]  Hardie, T., Ed., "Transport Protocol Path Signals",RFC 8558, DOI 10.17487/RFC8558, April 2019,              <https://www.rfc-editor.org/info/rfc8558>.Author's Address   Jari Arkko   Ericsson   Email: jari.arkko@ericsson.comArkko                    Expires 26 August 2021                 [Page 6]

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