Transport parameters for 0-RTT connections

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Authors Nicolas Kuhn  , Stephan Emile  , Gorry Fairhurst 
Last updated 2019-05-21
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Internet Engineering Task Force                             N. Kuhn, Ed.
Internet-Draft                                                      CNES
Intended status: Informational                           E. Stephan, Ed.
Expires: November 22, 2019                                        Orange
                                                       G. Fairhurst, Ed.
                                                  University of Aberdeen
                                                            May 21, 2019

               Transport parameters for 0-RTT connections


   The NewSessionTicket record carries a field that tells a client the
   volume of early data that it can include in the 0-RTT messages when
   reconnecting to the same peer.  There are cases where additional
   information can significantly improve the time-to-service.  This memo
   discusses a solution where path adaptation parameters are also shared
   between the peers.  There are use cases where this can accelerate the
   throughput of subsequent 0-RTT connections in both direction.

Status of This Memo

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   carefully, as they describe your rights and restrictions with respect
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  QUIC connection establishment: differences between 1-RTT and
       0-RTT connections . . . . . . . . . . . . . . . . . . . . . .   3
   3.  End-to-end solution . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Description of the extension in the NewSessionTicket  . .   3
     3.2.  Usage of the extension in the NewSessionTicket  . . . . .   4
   4.  Best current practice . . . . . . . . . . . . . . . . . . . .   4
   5.  What happens when BDP is used incorrectly?  . . . . . . . . .   6
   6.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     10.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   The 0-RTT mechanism is designed to accelerate the throughput when
   establishing a connection.  There are cases where 0-RTT alone does
   not improve the time-to-service, and additional information can
   therefore be beneficial.

   Some network paths result in a reduced time-to-service because the
   default parameters controlling the initialization of the transport
   and congestion control are not suitable for the path characteristics.
   QUIC's congestion control is based on TCP NewReno
   [I-D.ietf-quic-recovery] and the recommended initial window is
   defined by [RFC6928].  A path with a large bandwidth delay product
   can therefore significantly increase the time-to-service (e.g. a path
   using satellite communication [IJSCN19] could observe a much longer
   page load time for complex pages).

   This memo describes a solution where:

   1.  the server learns a fundamental characteristic of the path during
       the 1-RTT phase;

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   2.  the server sends this information to the client at the end of the
       1-RTT phase;

   3.  the server and the client exploit the information to improve the
       time-to-service during subsequent 0-RTT connections.

2.  QUIC connection establishment: differences between 1-RTT and 0-RTT

   This section recalls how 1-RTT and 0-RTT operate in QUIC

   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 the learned
   information about the session to the client in an opaque session
   ticket (see section 4.6.1 of [RFC8446]).  This information within the
   opaque ticket is 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' that
   indicates to the client the maximum size of application data to
   insert in the 0-RTT message.

3.  End-to-end solution

   This section proposes an improvement of the initialization of 0-RTT
   connections over high BDP networks where the client recalls, among
   other parameters, 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] that
   has been shown to improve performance both for high BDP and more
   common BDP [CONEXT15] [ICC16].

3.1.  Description of the extension in the NewSessionTicket

   This document defines an extension named "BDP_metadata" for the
   NewSessionTicket.  This structure contains the following parameters:
   BDP, MTU, RTT, loss-rate.

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3.2.  Usage of the extension in the NewSessionTicket

   At the end of a 1-RTT connection, a server can send information in a
   NewSessionTicket that describes the path to the client.  The message
   includes an additional 'extensions' field named 'BDP_metadata'.  The
   client stores this session ticket and the 'BDP_metadata' field.

   When the client reconnects to the same 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_metadata'
   field.  (The client does not send the 'BDP_metadata' field back to
   the server).  The server receives the session ticket and extracts the
   BDP context.  As example, it can use this message to provide
   information that may allow the congestion controller to provide a
   throughput closer to the capacity of the path.

   Because the path characteristics can change over time, and may hence
   become invalid for use in a subsequent connection, the server sets
   the age of the ticket (see section of [RFC8446]) to a short
   duration.  A server could also update the ticket when the path
   characteristics of connection are known to have changed.

4.  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 this
   information is opaque to the client.  The presence of the
   "BDP_metadata" extension field in the NewSessionTicket informs the
   client that the server can actively take action to improve its
   throughput when the session will restart.

   The following list describes 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 section.

   o  A client aware of a high BDP path: 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".  In addition to the default transport
      parameters used by the server, a server that knows that the path
      has a large BDP can let the client adapt its parameters.

   o  PMTU: Knowledge of the PMTU of a previous path improves the time
      to service because it reduces the duration of the path validation
      process described in section 8.2 of [I-D.ietf-quic-transport].

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   o  Connection RTT: The knowledge of the characteristics of a previous
      connection RTT can improve the throughput because a server can
      safely improve the slow start: e.g. using the 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; (e.g., this could
      reduce 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         |           +'extension' field |
                |            + early_data      |
                |            + BDP_metadata    |
                |              + BDP           |
                |              + RTT           |
                |              + loss-rate     |
                |              + MTU           |
              |          0 RTT connection         |
                |                              |
                |+'opaque' field               | +-------------------+
                |                              | |param adaptation   |
                |                              | |e.g.               |
                |                              | |tuned and paced IW |
                |                              | +-------------------+
                |                              |
                +<----+data transmission+----->+
                |                              |
                +                              +

                Figure 1: Example of opaque ticket content

5.  What happens when BDP is used incorrectly?

   This section discusses the impact of a server activating the
   'BDP_metadata' field when the network underneath actually has a small
   BDP.  This could happen when the server BDP estimate was incorrect,
   client has multiple paths to choose from and uses the ticket on a
   different path to which it was requested, or when the path
   characteristics change significantly.

   Depending on how the extension is exploited, this could result in
   assigning additional resources (e.g. buffer space) that later is not

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   used.  This could also motivate the requirement to pace the initial
   window to avoid transmitting data at a too high a rate.

6.  Discussion

   This mechanism 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_metadata' proposal
   aims at improving ingress traffic to the client.  Improving the
   ingress traffic can result in significant improvement to the quality-
   of-experience.  For example, this enables the use of transport
   parameters, such as the RTT, PMTU and BDP to adapt the initial data
   transmission of a 0-RTT connection.  In some large BDP deployment
   scenarios, this can halve the page load time of a web page download.

7.  Acknowledgements


8.  IANA Considerations

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

9.  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_metadata' field is visible by the
   client only.  An client that does not trust the server transport
   adaptation ignores any session ticket associated to a 'BDP_metadata'

   The server does not have to honour all the received requests (e.g.
   when it is resource-limited).

10.  References

10.1.  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,

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10.2.  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-20 (work in
              progress), April 2019.

              Thomson, M. and S. Turner, "Using TLS to Secure QUIC",
              draft-ietf-quic-tls-20 (work in progress), April 2019.

              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-20 (work
              in progress), April 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.

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   [RFC2488]  Allman, M., Glover, D., and L. Sanchez, "Enhancing TCP
              Over Satellite Channels using Standard Mechanisms",
              BCP 28, RFC 2488, DOI 10.17487/RFC2488, January 1999,

   [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,

   [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)


   Emile Stephan (editor)


   Gorry Fairhurst (editor)
   University of Aberdeen


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