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Internet Engineering Task Force                             N. Kuhn, Ed.
Internet-Draft                                                      CNES
Intended status: Informational                           E. Stephan, Ed.
Expires: September 12, 2019                                       Orange
                                                          March 11, 2019

               Transport parameters for 0-RTT connections


   0-RTT is designed to accelerate the egress throughput at the
   establishment of a connection.  There are cases where 0-RTT alone
   does not improve the time-to-service.

   This memo discusses a solution where a fundamental characteristic of
   the path is learned during the 1-RTT phase and shared with the 0-RTT
   phase to accelerate the initial throughput during subsequent 0-RTT

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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   This Internet-Draft will expire on September 12, 2019.

Copyright Notice

   Copyright (c) 2019 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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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect

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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  QUIC connection establishment . . . . . . . . . . . . . . . .   3
   3.  Large BDP connections . . . . . . . . . . . . . . . . . . . .   3
   4.  TCP split solution  . . . . . . . . . . . . . . . . . . . . .   4
   5.  End-to-end solution . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Description of the extension in the NewSessionTicket  . .   4
     5.2.  Usage of the extension in the NewSessionTicket  . . . . .   5
   6.  Best current practice . . . . . . . . . . . . . . . . . . . .   5
   7.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   9.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   8
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   11. Security Considerations . . . . . . . . . . . . . . . . . . .   8
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     12.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     12.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   0-RTT is designed to accelerate the throughput at the establishment
   of a connection.  There are cases where 0-RTT alone does not improve
   the time-to-service.

   As shown in [IJSCN19], the usage of a congestion control and
   transport initialization not adapted to satellite communication
   results in higher page loading time for heavy pages in a SATCOM
   context.  QUIC's congestion control is based on TCP NewReno
   [I-D.ietf-quic-recovery] and the recommended initial window is
   defined by [RFC6928].  This may not be suitable for good quality of
   experience for users in high Bandwidth Delay-Product (BDP) networks.

   This memo discusses a solution where a fundamental characteristic of
   the path is learned during the 1-RTT phase and shared with the 0-RTT
   phase to accelerate the initial throughput during subsequent 0-RTT

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2.  QUIC connection establishment

   This section recalls how 1-RTT and 0-RTT work.

   QUIC leverages the 2 handshakes of TLS1.3 [I-D.ietf-quic-tls].  The
   1-RTT handshake initiates a first set of credentials.  When a
   handshake achieves successfully, the server pushes information
   learned about the session to the client in an opaque session ticket
   (see section 4.6.1 of [RFC8446]).  The pieces of information of the
   ticket are meaningless to the client.  A client willing to establish
   a fast re-opening of the session pushes back this opaque 'ticket' in
   a 0-RTT handshake and sends early application data.

   In practice, the server sends the 'ticket' in a NewSessionTicket
   record [I-D.ietf-quic-tls].  The structure of the NewSessionTicket
   includes the opaque 'ticket' and an 'extensions' field.  The
   NewSessionTicket carries an additional field named 'early_data' which
   indicates to the client the maximal size of application data to
   insert in the 0-RTT message.

3.  Large BDP connections

   GEO-satellite based systems characteristics differ from terrestrial
   networks with:

   o  A large propagation delay of at least 250ms one-way delay;

   o  A high bit-rate in case of mobile users or when a user connects
      behind a box using Wi-Fi;

   o  Highly asymmetric links.

   These characteristics have an impact on end-to-end congestion

   o  Transport initialization: the 3-way handshake takes a long time
      reducing the time at which actual data can be transmitted;

   o  Maximum windows sizing: to fully exploit the bottleneck capacity,
      the high BDP may induce an important number of in-flights packets;

   o  Reliability: packet losses detection and correction is slow and
      the time needed for the end server to react to a congestion event
      may not be relevant;

   o  Getting up to speed: the exponential increase of the data rate
      transmission for a channel capacity probing is slowed down when
      the RTT is high.

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4.  TCP split solution

   High BDP networks commonly break the TCP end-to-end paradigm to adapt
   the transport protocol.  Splitting TCP allows adaptations to this
   specific use-case and assessing the issues discussed in section
   Section 3.  PEP [RFC3135] are commonly deployed in SATCOM
   infrastructure for that purpose and their deployment can result in
   50% page load time reduction in a SATCOM use-case [ICCRG100].

   [NCT13] and [RFC3135] describe the main functionalities of SATCOM TCP
   split solutions.  Shortly, for traffic going from a gateway to an end
   user behind a terminal, the TCP split intercepts TCP SYN to act as
   the end user and adapt the data rate transmission to the SATCOM
   scenario.  The TCP split specifically tune the TCP parameters to the
   context (latency, available capacity) that is measured.

   One important advantage of a TCP split solution is that it does not
   require any end-to-end modifications and is independent for both
   client and server sides.  That being said, this comes with a
   drawback: TCP splitters can hardly embed the most recent end-to-end
   improvements (e.g.  ECN or TCP Fast Open support).

5.  End-to-end solution

   This section proposes an improvement of the initialization of 0-RTT
   connections over satellite communication where the client recalls the
   BDP previously measured by the server during the 1-RTT handshake.
   The approach follows the tuning of the initial window described in
   [I-D.irtf-iccrg-sallantin-initial-spreading] which has been shown to
   improve performance both for high BDP and more common BDP

5.1.  Description of the extension in the NewSessionTicket

   A new extension named "BDP_data" is defined for NewSessionTicket.  It
   contains the following value: BDP_value, that is the value in bits
   (same unit as [RFC6349]).  The reception of the field BDP_data
   provides the client with 3 indications:

   o  The path with this server has a large BDP;

   o  The server added the path characteristics in the opaque 'ticket'

   o  The server will optimize the reopening of the session upon
      reception of this opaque ticket.

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5.2.  Usage of the extension in the NewSessionTicket

   A server measures a connection BDP far larger than usual.  It
   includes the path characteristics in the opaque ticket it sends to
   the client in a NewSessionTicket message.  The message includes an
   additional 'extensions' field named 'BDP_data'.  The client stores
   the session ticket and the 'BDP_data' field.

   When the client reconnects to this server in 0-RTT mode, it pushes
   back this session ticket in the ClientHello and prepares itself to
   receive data in the context given by the 'BDP_data' field (The client
   does not send the 'BDP_data' field back to the server).  The server
   receives the session ticket and extracts the BDP context.  It uses
   this information to provide a throughput closer to the capacity of
   the path.

   As the validity of the path characteristics may change over the time
   the server sets the age of the ticket (see section of
   [RFC8446]) to a short duration or updates the ticket when the path
   characteristics of the current connection changes.

6.  Best current practice

   This section provides examples of data that could be added in the
   opaque ticket field by the server.  The details added by the server
   in the session ticket do not need to be standardized for
   interoperability between QUIC clients and servers because it is
   opaque to the client.  The presence of the "BDP_data" extension field
   in the NewSessionTicket informs the client that the server will
   actively take action to improve its throughput when the session will

   Here are examples of information elements set by the server in the
   session ticket to accompany the signaling of field.  These examples
   are illustrated in Figure 1 and their purpose is detailed in this

   o  client aware of the high BDP: The section 7.3.1 of
      [I-D.ietf-quic-transport] indicates that the "A client that
      attempts to send 0-RTT data MUST remember the transport parameters
      used by the server".  On top of other transport parameters used by
      the server, knowing that the BDP is high let the client adapt
      parameters specifically.  As example, the client could adapt the
      ACK ratio following the discussion in Issue 1978 of the GITHUB

   o  PMTU: The knowledge of the MTU of the previous path improves the
      time to service because it reduces the duration of the path

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      validation process described in section 8.2 of

   o  connection RTT: The knowledge of the characteristics of the
      previous connection RTT improves the throughput because the server
      can safely improve the slow start: e.g. using pacing models of
      [I-D.irtf-iccrg-sallantin-initial-spreading] can result in high IW
      for high RTT paths and a common IW for paths with smaller RTT.
      The results presented in [ICC16] show that for both files of 15 kB
      and 750 kB, the proposed solution reduces the time to download by
      approximatively 2 seconds whether the RTT is 50ms or 500ms.

   o  ticket_lifetime: The server sets a shorter validity duration to
      avoid receiving obsolete path characteristics later; as an example
      it reduces the validity to one day.

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              CLIENT                         SERVER
              |          1 RTT connection         |
                 |                              |
                 +<---1-RTT TLS1.3 HANDSHAKE--->+
                 |                              | +------------+
                 +<-----data transmission------>+ |path charact|
                 |                              | |record      |
                 |                              | +------------+
    Client aware |           +ticket_lifetime   |
    of high BDP  |           +'opaque' field    |
    path         |            + ...             |
                 |            + PMTU            |
                 |            + connection RTT  |
                 |           +'extension' field |
                 |            + early_data      |
                 |            + BDP_data        |
                 |                              |
              |          0 RTT connection         |
                 |                              |
                 |+'opaque' field               | +-------------------+
                 | + ...                        | |param adaptation   |
                 | + PMTU                       | |e.g.               |
                 | + connection RTT             | |tuned and paced IW |
                 |                              | +-------------------+
                 |                              |
                 +<----+data transmission+----->+
                 |                              |
                 +                              +

                Figure 1: Example of opaque ticket content

7.  Discussion

   The proposal made in this draft follows the approach of the extension
   field 'early_data' of the NewSessionTicket of TLS1.3.  While
   'early_data' improves the egress traffic of a client, the 'BDP_data'
   proposal aims at improving its ingress traffic.  Improving the
   ingress traffic of an end user can result in drastic quality-of-
   experience improvements.  As example, this contribution enables the
   exploitation of the RTT, PMTU and BDP to adapt the initial data
   transmission of a 0-RTT connection to halve the page load time of a
   web page download.

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8.  Acknowledgements


9.  Contributors


10.  IANA Considerations

   TBD: text is required to register the extension BDP_data field.

11.  Security Considerations

   The security is provided by the 1-RTT phase.  The measure of BDP is
   made during a previous connection.  The exchange and the information
   are protected both by the TLS encryption and the NewSessionTicket
   (see section 4.6.1 of [RFC8446]).

   The BDP information the server will received is protected in the
   opaque session ticket.  The 'BDP_data' field is visible by the client
   only.  An client which does not trust the server transport adaptation
   ignores any session ticket associated to a 'BDP_data' field.

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

12.2.  Informative References

              Li, Q., Dong, M., and P. Godfrey, "Halfback: Running Short
              Flows Quickly and Safely", ACM CoNEXT , 2015.

              Iyengar, J. and I. Swett, "QUIC Loss Detection and
              Congestion Control", draft-ietf-quic-recovery-18 (work in
              progress), January 2019.

              Thomson, M. and S. Turner, "Using TLS to Secure QUIC",
              draft-ietf-quic-tls-18 (work in progress), January 2019.

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              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-18 (work
              in progress), January 2019.

              Pauly, T., Schinazi, D., and C. Wood, "TLS Ticket
              Requests", draft-ietf-tls-ticketrequests-00 (work in
              progress), January 2019.

              Sallantin, R., Baudoin, C., Arnal, F., Dubois, E., Chaput,
              E., and A. Beylot, "Safe increase of the TCP's Initial
              Window Using Initial Spreading", draft-irtf-iccrg-
              sallantin-initial-spreading-00 (work in progress), January

   [ICC16]    Sallantin, R., Baudoin, C., Chaput, E., Arnal, F., Dubois,
              E., and A-L. Beylot, "Reducing web latency through TCP IW:
              Be smart", IEEE ICC , 2016.

              Kuhn, N., "MPTCP and BBR performance over Internet
              satellite paths", IETF ICCRG 100, 2017.

   [IJSCN19]  Thomas, L., Dubois, E., Kuhn, N., and E. Lochin, "Google
              QUIC performance over a public SATCOM access",
              International Journal of Satellite Communications and
              Networking , 2019.

   [NCT13]    Pirovano, A. and F. Garcia, "A new survey on improving TCP
              performances over geostationary satellite link", Network
              and Communication Technologies , 2013.

   [RFC3135]  Border, J., Kojo, M., Griner, J., Montenegro, G., and Z.
              Shelby, "Performance Enhancing Proxies Intended to
              Mitigate Link-Related Degradations", RFC 3135,
              DOI 10.17487/RFC3135, June 2001,

   [RFC6349]  Constantine, B., Forget, G., Geib, R., and R. Schrage,
              "Framework for TCP Throughput Testing", RFC 6349,
              DOI 10.17487/RFC6349, August 2011,

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   [RFC6928]  Chu, J., Dukkipati, N., Cheng, Y., and M. Mathis,
              "Increasing TCP's Initial Window", RFC 6928,
              DOI 10.17487/RFC6928, April 2013,

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

Authors' Addresses

   Nicolas Kuhn (editor)
   18 Avenue Edouard Belin
   Toulouse  31400

   Email: nicolas.kuhn@cnes.fr

   Emile Stephan (editor)
   2, avenue Pierre Marzin
   Lannion  22300

   Email: emile.stephan@orange.com

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