QUIC                                                    B. Trammell, Ed.
Internet-Draft                                             M. Kuehlewind
Intended status: Experimental                                 ETH Zurich
Expires: April 26, 2019                                 October 23, 2018

                       The QUIC Latency Spin Bit


   This document specifies the addition of a latency spin bit to the
   QUIC transport protocol and describes how to use it to measure end-
   to-end latency.

Note to Readers

   This document specifies an experimental delta to the QUIC transport
   protocol.  Specifically, this experimentation is intended to

   o  the impact of the addition of the latency spin bit on
      implementation and specification complexity; and

   o  the accuracy and value of the information derived from spin bit
      measurement on live network traffic.

   The information generated by this experiment will be used by the QUIC
   working group as input to a decision about the standardization of the
   latency spin bit.  Although this is a Working Group document, it is
   currently NOT a Working Group deliverable.

   Discussion of this draft takes place on the QUIC working group
   mailing list (quic@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/search/?email_list=quic [1].

   Working Group information can be found at https://github.com/quicwg
   [2]; source code and issues list for this draft can be found at
   https://github.com/quicwg/base-drafts/labels/-spin [3].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute

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   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 26, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  The Spin Bit Mechanism  . . . . . . . . . . . . . . . . . . .   3
     2.1.  Proposed Short Header Format Including Spin Bit . . . . .   3
     2.2.  Setting the Spin Bit on Outgoing Packets  . . . . . . . .   4
     2.3.  Resetting Spin Value State  . . . . . . . . . . . . . . .   4
   3.  Using the Spin Bit for Passive RTT Measurement  . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security and Privacy Considerations . . . . . . . . . . . . .   6
   6.  Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Since draft-ietf-spin-exp-00  . . . . . . . . . . . . . .   6
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
     8.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

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1.  Introduction

   The QUIC transport protocol [QUIC-TRANSPORT] uses Transport Layer
   Security (TLS) [TLS] to encrypt most of its protocol internals.  In
   contrast to TCP where the sequence and acknowledgement numbers and
   timestamps (if the respective option is in use) can be seen by on-
   path observers and used to estimate end-to-end latency, QUIC's wire
   image (see [WIRE-IMAGE]) currently does not expose any information
   that can be used for passive latency measurement techniques that rely
   on this information (e.g.  [CACM-TCP], [TMA-QOF]).

   This document adds an explicit signal for passive latency
   measurability to the QUIC short header: a "spin bit".  Passive
   observation of the spin bit provides one RTT sample per RTT to
   passive observers of QUIC traffic.  This document describes the
   mechanism, how it can be added to QUIC, and how it can be used by
   passive measurement facilities to generate RTT samples.

2.  The Spin Bit Mechanism

   The latency spin bit enables latency monitoring from observation
   points on the network path throughout the duration of a connection.
   Since it is possible to measure handshake RTT without a spin bit, it
   is sufficient to include the spin bit in the short packet header.
   The spin bit therefore appears only after version negotiation and
   connection establishment are completed.

2.1.  Proposed Short Header Format Including Spin Bit

   As of the current editor's version of [QUIC-TRANSPORT], this proposal
   specifies using the sixth most significant bit (0x04) of the first
   octet in the short header for the spin bit.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |0|K|1|1|0|S|R R|
   |                Destination Connection ID (0..144)           ...
   |                      Packet Number (8/16/32)                ...
   |                     Protected Payload (*)                   ...

         Figure 1: Short Header Format including proposed Spin Bit

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   S: The Spin bit is set 0 or 1 depending on the stored spin value that
   is updated on packet reception as explained in Section 2.2.

   R: Two additional bits are reserved for experimentation in the short

2.2.  Setting the Spin Bit on Outgoing Packets

   Each endpoint, client and server, maintains a spin value, 0 or 1, for
   each QUIC connection, and sets the spin bit in the short header to
   the currently stored value when a packet with a short header is sent
   out.  The spin value is initialized to 0 at each endpoint, client and
   server, at connection start.  Each endpoint also remembers the
   highest packet number seen from its peer on the connection.

   The spin value is then determined at each endpoint within a single
   connection as follows:

   o  When the server receives a packet from the client, if that packet
      has a short header and if it increments the highest packet number
      seen by the server from the client, the server sets the spin value
      to the value observed in the spin bit in the received packet.

   o  When the client receives a packet from the server, if the packet
      has a short header and if it increments the highest packet number
      seen by the client from the server, it sets the spin value to the
      opposite of the spin bit in the received packet.

   This procedure will cause the spin bit to change value in each
   direction once per round trip.  Observation points can estimate the
   network latency by observing these changes in the latency spin bit,
   as described in Section 3.  See [QUIC-SPIN] for further illustration
   of this mechanism in action.

2.3.  Resetting Spin Value State

   Each client and server resets it spin value to zero when sending the
   first packet of a given connection with a new connection ID.  This
   reduces the risk that transient spin bit state can be used to link
   flows across connection migration or ID change.

3.  Using the Spin Bit for Passive RTT Measurement

   When a QUIC flow sends data continuously, the latency spin bit in
   each direction changes value once per round-trip time (RTT).  An on-
   path observer can observe the time difference between edges (changes
   from 1 to 0 or 0 to 1) in the spin bit signal in a single direction
   to measure one sample of end-to-end RTT.

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   An observer can store the largest observed packet number per flow,
   and reject edges that do not have a monotonically increasing packet
   number (greater than the largest observed packet number).  This will
   avoid detecting spurious edges caused by reordering events that
   include an edge, which would lead to very low RTT estimates if not

   If the spin bit edge occurs after a long packet number gap, it should
   be ignored: this filters out high RTT estimates due to loss of an
   actual edge in a burst of lost packets.

   Note that this measurement, as with passive RTT measurement for TCP,
   includes any transport protocol delay (e.g., delayed sending of
   acknowledgements) and/or application layer delay (e.g., waiting for a
   request to complete).  It therefore provides devices on path a good
   instantaneous estimate of the RTT as experienced by the application.
   A simple linear smoothing or moving minimum filter can be applied to
   the stream of RTT information to get a more stable estimate.

   However, application-limited and flow-control-limited senders can
   have application and transport layer delay, respectively, that are
   much greater than network RTT.  When the sender is application-
   limited and e.g. only sends small amount of periodic application
   traffic, where that period is longer than the RTT, measuring the spin
   bit provides information about the application period, not the
   network RTT.

   Simple heuristics based on the observed data rate per flow or changes
   in the RTT series can be used to reject bad RTT samples due to
   application or flow control limitation; for example, QoF [TMA-QOF]
   rejects component RTTs significantly higher than RTTs over the
   history of the flow.  These heuristics may use the handshake RTT as
   an initial RTT estimate for a given flow.

   An on-path observer that can see traffic in both directions (from
   client to server and from server to client) can also use the spin bit
   to measure "upstream" and "downstream" component RTT; i.e, the
   component of the end-to-end RTT attributable to the paths between the
   observer and the server and the observer and the client,
   respectively.  It does this by measuring the delay between a spin
   edge observed in the upstream direction and that observed in the
   downstream direction, and vice versa.

4.  IANA Considerations

   This document has no actions for IANA.

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5.  Security and Privacy Considerations

   The spin bit is intended to expose end-to-end RTT to observers along
   the path, so the privacy considerations for the latency spin bit are
   essentially the same as those for passive RTT measurement in general.
   It has been shown [PAM-RTT] that RTT measurements do not provide more
   information for geolocation than is available in the most basic,
   freely-available IP address based location databases.  The risk of
   exposure of per-flow network RTT to on-path devices is therefore

6.  Change Log

      *RFC Editor's Note:* Please remove this section prior to
      publication of a final version of this document.

6.1.  Since draft-ietf-spin-exp-00

   Nothing yet.


   This document is derived from [QUIC-SPIN], which was the work of the
   following authors in addition to the editor of this document:

   o  Piet De Vaere, ETH Zurich

   o  Roni Even, Huawei

   o  Giuseppe Fioccola, Telecom Italia

   o  Thomas Fossati, Nokia

   o  Marcus Ihlar, Ericsson

   o  Al Morton, AT&T Labs

   o  Emile Stephan, Orange

   The QUIC Spin Bit was originally specified in a slightly different
   form by Christian Huitema.

   This work is partially supported by the European Commission under
   Horizon 2020 grant agreement no. 688421 Measurement and Architecture
   for a Middleboxed Internet (MAMI), and by the Swiss State Secretariat
   for Education, Research, and Innovation under contract no. 15.0268.
   This support does not imply endorsement.

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8.  References

8.1.  Normative References

              Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", draft-ietf-quic-
              transport-15 (work in progress), October 2018.

8.2.  Informative References

              Strowes, S., "Passively Measuring TCP Round-Trip Times (in
              Communications of the ACM)", October 2013.

   [PAM-RTT]  Trammell, B. and M. Kuehlewind, "Revisiting the Privacy
              Implications of Two-Way Internet Latency Data (in Proc.
              PAM 2018)", March 2018.

              Trammell, B., Vaere, P., Even, R., Fioccola, G., Fossati,
              T., Ihlar, M., Morton, A., and S. Emile, "Adding Explicit
              Passive Measurability of Two-Way Latency to the QUIC
              Transport Protocol", draft-trammell-quic-spin-03 (work in
              progress), May 2018.

   [TLS]      Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,

   [TMA-QOF]  Trammell, B., Gugelmann, D., and N. Brownlee, "Inline Data
              Integrity Signals for Passive Measurement (in Proc. TMA
              2014)", April 2014.

              Trammell, B. and M. Kuehlewind, "The Wire Image of a
              Network Protocol", draft-trammell-wire-image-04 (work in
              progress), April 2018.

8.3.  URIs

   [1] https://mailarchive.ietf.org/arch/search/?email_list=quic

   [2] https://github.com/quicwg

   [3] https://github.com/quicwg/base-drafts/labels/-spin

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Authors' Addresses

   Brian Trammell (editor)
   ETH Zurich

   Email: ietf@trammell.ch

   Mirja Kuehlewind
   ETH Zurich

   Email: mirja.kuehlewind@tik.ee.ethz.ch

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