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Versions: 00 draft-huitema-quic-ts

Network Working Group                                         C. Huitema
Internet-Draft                                      Private Octopus Inc.
Intended status: Experimental                            January 3, 2020
Expires: July 6, 2020


            Quic ACK Timestamps For Measuring One-Way Delays
                       draft-huitema-quic-1wd-00

Abstract

   The QUIC extension for one way delay mesurements adds a single
   timestamp to the ACK frame.  The timestamp is set to the number of
   microseconds from the beginning of the connection to the time at
   which the ACK frame is sent.  The draft defines the
   "enable_one_way_delay" transport parameter for negotiating the
   extension, and two new frame types for timestamped ACK with or
   without ECN counts.

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 July 6, 2020.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   include Simplified BSD License text as described in Section 4.e of



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

Table of Contents

   1.  Measuring One-Way Delays  . . . . . . . . . . . . . . . . . .   2
     1.1.  Terms and Definitions . . . . . . . . . . . . . . . . . .   3
   2.  Specification . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Negotiation . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Timestamped ACK format  . . . . . . . . . . . . . . . . . . .   3
     3.1.  RTT Measurements  . . . . . . . . . . . . . . . . . . . .   4
     3.2.  One-Way Delay Measurements  . . . . . . . . . . . . . . .   4
   4.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Measuring One-Way Delays

   The QUIC Transport Protocol [I-D.ietf-quic-transport] provides a
   secure, multiplexed connection for transmitting reliable streams of
   application data.  The algorithms for QUIC Loss Detection and
   Congestion Control [I-D.ietf-quic-recovery] use measurement of Round
   Trip Time (RTT) to determine when packets should be retransmitted.
   RTT measurements are useful, but there are however many cases in
   which more precise One-Way Delay (1WD) measurements enable more
   efficient Loss Detection and Congestion Control.

   An example would be the Low Extra Delay Background Transport (LEDBAT)
   [RFC6817] which uses variations in transmission delay to detect
   competition for transmission resource.  Experience shows that while
   LEDBAT may be implemented using RTT measurements, it is somewhat
   inefficient because it will cause unnecessary slowdowns in case of
   queues or delayed ACKs on the return path.  Using 1WD solves these
   issues.  Similar argument can be made for most delay-based
   algorithms.

   We propose to enable one way delay measurements in QUIC by extending
   the ACK or ACK-ECN format with a timestamp field.  The use of this
   extended format is negotiated with a transport parameter,
   "enable_one_way_delay".  When the extension is negotiated by both
   parties, the format of the ACK and ACK ECN frames is extended with
   the timestamp field.





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1.1.  Terms and Definitions

   The keywords "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.

2.  Specification

   The enable_one_way_delay transport parameter used for negotiating the
   extension is defined in Section 2.1.  The Timestamped ACK frame
   format is defined in Section 3.

2.1.  Negotiation

   The one way delay extension is negotiated using a transport
   parameter:

   enable_one_way_delay (TBD):  The enable one-way delay transport
      parameter is included if the endpoint support one way delay
      measurements for this connection.  This parameter has a zero-
      length value.

   Negotiation is successful if both peers support include this
   parameter in their transport parameter message.  If negotiation is
   successful the peers MUST send Timestamped ACK instead of the
   standard ACK frames in all 1RTT protected packets.  The peers MUST
   NOT send Timestamped ACK in packets of other types, such as Initial,
   Handshake or 0RTT protected packet.

   Receiving a Timestamped ACK frame when not expected MUST be treated
   as a Protocol Error.  Similarly, receiving a standard ACK frame when
   a Timestamped ACK frame is expected MUST be treated as a Protocol
   Error.

3.  Timestamped ACK format

   Timestamped ACK are identified by the frame type:

   o  Timestamped_ACK (TBD, TBD+1)

   If the frame type is TBD+1, Timestamped ACK frames also contain the
   sum of QUIC packets with associated ECN marks received on the
   connection up until this point.

   The format of the Timestamped ACK frames is similar to that of the
   standard ACK Frames defined in section 19.3 of



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   [I-D.ietf-quic-transport], with the addition of the Time Stamp
   parameter.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Largest Acknowledged (i)                ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Time Stamp (i)                     ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          ACK Delay (i)                      ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       ACK Range Count (i)                   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       First ACK Range (i)                   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          ACK Ranges (*)                     ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          [ECN Counts]                       ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 1: ACK Frame Format with Time Stamp

   The timestamp encodes the number of microseconds since the beginning
   of the connection, as measured by the peer at the time at which the
   ACK is sent.  It is encoded using the exponent selected by the peer
   in the ack_delay_exponent.  The exponent reduced time stamp is
   encoded in the ACK frame as a variable length integer.

3.1.  RTT Measurements

   RTT measurements are performed as specified in Section 4 of
   [I-D.ietf-quic-recovery], without reference to the Timestamp
   parameter of the Timestamped ACK frames.

3.2.  One-Way Delay Measurements

   An endpoint generates a One Way Delay Sample on receiving a
   TimeStamped ACK frame that meets the following two conditions:

   o  the largest acknowledged packet number is newly acknowledged, and

   o  at least one of the newly acknowledged packets was ack-eliciting.

   The One Way Delay sample, latest_1wd, is generated as the time
   elapsed since the largest acknowledged packet was sent, corrected for
   the difference between local time at the sending peer and connection
   time at the receiving peer, phase_shift.



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   latest_1wd = time_stamp - send_time_of_largest_acked - phase_shift

   By convention, the phase_shift is estimated upon reception of the
   first RTT sample, first_rtt.  It is set to:

   phase_shift = time_stamp - send_time_of_largest_acked - latest_rtt/2

   In that formula, we assume that the local time are measured in
   microseconds since the beginning of the connection.

   We understand that clocks may drift over time, and that simply
   estimating a phase shift at the beginning of a connection may be too
   simplistic for long duration connections.  Implementations MAY adopt
   different strategies to reestimate the phase shift at appropriate
   intervals.  Specifying these strategies is beyond the scope of this
   document.

4.  Discussion

   This document makes a series of choices in implementing one way delay
   measurements.  The two important choices are the decision to only
   have one timestamp per Timestamped ACK frame, and to use new frame
   types for the Timestamped ACK frames.

   In theory, it would be possible to augment the ACK frame format and
   document the delay of every frame received.  The current proposal is
   simpler, and creates less overhead.  It is also sufficient for the
   intended usage, which is to improve the efficiency of congestion
   control protocols.

   Once the extension is negotiated, it would be possible in theory to
   reuse the existing ACK frame type and just associate it with the
   timestamp format.  This would spare us the need to reserve two frame
   type numbers for the new format.  However, this simplification would
   introduce a dependency between the state of the parser and the state
   of the connection.  This dependency is hard to manage in off-line
   usages such as parsing log files.

5.  Security Considerations

   The Timestamp value in the Timestamp ACK is asserted by the sender of
   the ACK.  Adversarial peers could chose values of the time stamp
   designed to exercise side effects in congestion control algorithms or
   other algorithms relying on the one-way delays.  This can be
   mitigated by running plausibility checks on the received values.  For
   example, each peer can maintain statistics not just on the One Way
   Delays, but also on the differences between One Way Delays and RTT,
   and detect outlier values.  Peers can also compare the differences



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   between timestamps of successive acknowledgements and the differences
   between the sending times of corresponding packets, and detect
   anomalies if the delays between acknowledging packets appears shorter
   than the delays when sending them.

6.  IANA Considerations

   This document registers a new value in the QUIC Transport Parameter
   Registry:

   Value: TBD (using value 0x10DE in early deployments)

   Parameter Name: enable_one_way_delay

   Specification: Indicates that the connection should use TimeStamped
   ACK frames

   This document also registers a new value in the QUIC Frame Type
   registry:

   Value: 0x34 and 0x35 (if this document is approved)

   Frame Name: Timestamped ACK

   Specification: ACK frames augmented with a timestamp

7.  References

7.1.  Normative References

   [I-D.ietf-quic-recovery]
              Iyengar, J. and I. Swett, "QUIC Loss Detection and
              Congestion Control", draft-ietf-quic-recovery-24 (work in
              progress), November 2019.

   [I-D.ietf-quic-transport]
              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-24 (work
              in progress), November 2019.

   [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/info/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/info/rfc8174>.



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7.2.  Informative References

   [RFC6817]  Shalunov, S., Hazel, G., Iyengar, J., and M. Kuehlewind,
              "Low Extra Delay Background Transport (LEDBAT)", RFC 6817,
              DOI 10.17487/RFC6817, December 2012,
              <https://www.rfc-editor.org/info/rfc6817>.

Author's Address

   Christian Huitema
   Private Octopus Inc.
   427 Golfcourse Rd
   Friday Harbor  WA 98250
   U.S.A

   Email: huitema@huitema.net



































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