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Internet Engineering Task Force                                  N. Kuhn
Internet-Draft                                                      CNES
Intended status: Informational                              G. Fairhurst
Expires: January 4, 2020                          University of Aberdeen
                                                               J. Border
                                             Hughes Network Systems, LLC
                                                              E. Stephan
                                                                  Orange
                                                            July 3, 2019


                            QUIC for SATCOM
                        draft-kuhn-quic-4-sat-00

Abstract

   QUIC's congestion control is not designed for operating over an
   Internet path with a high BDP.  This limits the user experience.
   Moreover, a path can combine satellites network segment together with
   a wide variety of other network technologies (Ethernet, cable modems,
   WiFi, cellular, radio links, etc): this complicates the
   characteristics of the end-to-end path.  If this is not addressed,
   the end-to-end quality of experience will be degraded.

   This memo identifies the characteristics of a SATCOM link that impact
   the operation of the QUIC transport protocol and proposes best
   current practice to ensure acceptable protocol performance.

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 January 4, 2020.







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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
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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.  Operating over a path with a large BDP  . . . . . . . . . . .   3
   3.  TCP Split Solution  . . . . . . . . . . . . . . . . . . . . .   4
   4.  Mechanisms that improve the performance of QUIC for SATCOM  .   4
     4.1.  Getting up to speed . . . . . . . . . . . . . . . . . . .   4
     4.2.  Reliability . . . . . . . . . . . . . . . . . . . . . . .   5
     4.3.  Maximum window  . . . . . . . . . . . . . . . . . . . . .   5
     4.4.  ACK ratio . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     10.2.  Informative References . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The end-to-end performance of an application using an Internet path
   can be impacted by the Bandwidth-Delay Product (BDP) of the links and
   network devices forming the path.  For instance, the page load time
   for a complex page can be much larger when the path includes a
   satellite link.  A significant contribution to this reduced
   performance arises from the initialisation and design of transport
   mechanisms.  QUIC's congestion control is based on TCP NewReno
   [I-D.ietf-quic-recovery] and the recommended initial window is
   defined by [RFC6928].





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   Moreover, satellite communications (SATCOM) systems have long been
   used to support point-to-point links and specialised networks.  The
   predominate current use is as a link-layer for Internet Protocols.
   Typical example applications include: use as an access technology for
   remote locations, backup and rapid deployment of new services,
   transit networks and backhaul of various types of IP networks, and
   provision to mobile (maritime, aircraft, etc.).  The satellite IP
   network segment usually only forms one part of the end-to-end path.
   This means user traffic can experince a path that includes satellite
   link together with a wide variety of other network technologies
   (Ethernet, cable modems, WiFi, cellular, radio links, etc).  Although
   a user can sometimes know the presence of the satellite service, a
   typical user does not deploy special software or applications because
   they expect a satellite network is being used.  Often a user is
   unaware of the technologies underpinning the links forming the
   network path.

   This memo identifies the characteristics of a SATCOM link that impact
   the operation of the QUIC transport protocol and proposes best
   current practice to ensure acceptable protocol performance.

2.  Operating over a path with a large BDP

   GEO-satellite based systems characteristics differ from paths only
   using terrestrial links in their path characteristics:

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

   o  Some systems can exhibit a high loss-rate (e.g. mobile users or
      users behind a Wi-Fi link);

   o  Employ radio resource management (often using techniques similar
      to cellular mobile or DOCSIS cable networks, but differing to
      accommodate the satellite propagation delay);

   o  Links can be highly asymmetric (in terms of capacity and one-way
      delay).

   More information on satellite links characteristics can be found in
   [RFC2488].

   These characteristics have an impact on the performance of end-to-end
   congestion controls:

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




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

   o  Reliability: packet loss detection and correction is slow (the
      performance of end-to-end retransmission is also impacted when
      using a high RTT path);

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

3.  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 2.  Satellite communications commonly deploy Performance
   Enhancement Proxy (PEP) for compression, caching and TCP acceleration
   services [RFC3135].  Their deployment can result in 50% page load
   time reduction in a SATCOM use-case [ICCRG100].

   [NCT13] and [RFC3135] describe the main functions of SATCOM TCP split
   solutions.  Shortly, for traffic originated at a gateway to an
   endpoint connected via a satellite terminal, the TCP split intercepts
   TCP SYN packets to act on behalf of the endpoint and adapt the data
   rate transmission to the SATCOM scenario.  The split solution
   specifically tunes the TCP parameters to the context (latency,
   available capacity).  The tuning can be achieved using a priori
   information about the satellite system and/or by measuring the
   properties of the network segment that includes the satellite system.

   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 often are unable to track the most recent
   end-to-end improvements (e.g.  ECN or TCP Fast Open support).  The
   methods configured in the split proxy usually continue to be used
   until a split solution is finally updated.  This can delay/negate the
   benefit of any end-to-end improvements.

4.  Mechanisms that improve the performance of QUIC for SATCOM

4.1.  Getting up to speed

   3-way handshake takes a long time reducing the time at which actual
   data can be transmitted.




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   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
   [CONEXT15][ICC16].

4.2.  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.  This happens when a user uses a Wi-Fi link to access a
   SATCOM terminal.  Although the benefits needed to weighed against the
   additional capacity in introducing end-to-end FEC and the potential
   to use link-local ARQ and/or link-adaptive FEC.

   Introducing network coding in QUIC could help in recovering from the
   residual Wi-Fi losses.

4.3.  Maximum window

   To fully exploit the bottleneck capacity, the high BDP may induce an
   important number of in-flights packets.

4.4.  ACK ratio

   Asymmetry in capacity (or in the way capacity is granted to a flow)
   can lead to cases where the throughput in one direction of
   communication is restricted by the acknowledgement traffic flowing in
   the opposite direction.  The limitations of specific underlying
   networks could be in terms of the volume of acknowledgement traffic
   (limited return path capacity) or in the number of acknowledgement
   packets (e.g., when a radio-resource management system has to track
   channel usage) or both.

   TCP Performance Implications of Network Path Asymmetry [RFC3449]
   describes a range of mechanisms that can mitigate the impact of path
   asymmetry.  One simple method is to tell the remote endpoint to send
   compound acknowledgments less frequently.  A rate of one ACK every
   RTT/4 can significantly reduce this traffic.

   Many of these mitigations have been deployed in satellite systems,
   often as a mechanism within a PEP.  Despite their benefits over paths
   with a high asymmetry of capacity, most mechanisms rely on being able
   to inspect and/or modify the transport layer header information of
   TCP ACK packets.  This is not possible when the transport layer
   information is encrypted.  The QUIC transport specification may
   evolve to allow the ACK Ratio to be adjusted.





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5.  Discussion

   Many of the issues identified already exist for any encrypted
   transport service that uses a path that employs encryption at the IP
   layer.  This includes endpoints that utilise IPsec at the network
   layer, or use VPN technology over the satellite network segment.
   These uses are unable to benefit from enhancement within the
   satellite network segment, and often the user is unaware of the
   presence of the satellite link on their path, except through
   observing the impact it has on the performance they experience.

6.  Acknowledgements

   None.

7.  Contributors

   None.

8.  IANA Considerations

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

9.  Security Considerations

   This document does not propose changes to the security functions
   provided by the QUIC protocol.  QUIC uses TLS encryption to protect
   the transport header and its payload.  Security is considered in the
   "Security Considerations" of cited IETF documents.

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,
              <https://www.rfc-editor.org/info/rfc2119>.

10.2.  Informative References

   [CONEXT15]
              Li, Q., Dong, M., and P. Godfrey, "Halfback: Running Short
              Flows Quickly and Safely", ACM CoNEXT , 2015.







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   [I-D.ietf-quic-recovery]
              Iyengar, J. and I. Swett, "QUIC Loss Detection and
              Congestion Control", draft-ietf-quic-recovery-20 (work in
              progress), April 2019.

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

   [I-D.ietf-quic-transport]
              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-20 (work
              in progress), April 2019.

   [I-D.ietf-tls-ticketrequests]
              Pauly, T., Schinazi, D., and C. Wood, "TLS Ticket
              Requests", draft-ietf-tls-ticketrequests-01 (work in
              progress), June 2019.

   [I-D.irtf-iccrg-sallantin-initial-spreading]
              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
              2014.

   [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.

   [ICCRG100]
              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.

   [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,
              <https://www.rfc-editor.org/info/rfc2488>.




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   [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,
              <https://www.rfc-editor.org/info/rfc3135>.

   [RFC3449]  Balakrishnan, H., Padmanabhan, V., Fairhurst, G., and M.
              Sooriyabandara, "TCP Performance Implications of Network
              Path Asymmetry", BCP 69, RFC 3449, DOI 10.17487/RFC3449,
              December 2002, <https://www.rfc-editor.org/info/rfc3449>.

   [RFC6349]  Constantine, B., Forget, G., Geib, R., and R. Schrage,
              "Framework for TCP Throughput Testing", RFC 6349,
              DOI 10.17487/RFC6349, August 2011,
              <https://www.rfc-editor.org/info/rfc6349>.

   [RFC6928]  Chu, J., Dukkipati, N., Cheng, Y., and M. Mathis,
              "Increasing TCP's Initial Window", RFC 6928,
              DOI 10.17487/RFC6928, April 2013,
              <https://www.rfc-editor.org/info/rfc6928>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

Authors' Addresses

   Nicolas Kuhn
   CNES

   Email: nicolas.kuhn@cnes.fr


   Godred Fairhurst
   University of Aberdeen

   Email: gorry@erg.abdn.ac.uk


   John Border
   Hughes Network Systems, LLC

   Email: border@hns.com








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   Emile Stephan
   Orange

   Email: emile.stephan@orange.com















































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