Internet DRAFT - draft-arkko-path-signals-information
draft-arkko-path-signals-information
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
draft-arkko-path-signals-information-00
Abstract
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 of BCP 78 and BCP 79.
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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
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.
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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
[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>.
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[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.com
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