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Internet Engineering Task Force                             N. Kuhn, Ed.
Internet-Draft                                                      CNES
Intended status: Informational                            E. Lochin, Ed.
Expires: August 31, 2018                                    ISAE-SUPAERO
                                                       February 27, 2018


                     Network coding and satellites
             draft-kuhn-nwcrg-network-coding-satellites-03

Abstract

   This memo presents the current deployment of network coding in some
   satellite telecommunications systems along with a discussion on the
   multiple opportunities to introduce these techniques at a wider
   scale.

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 August 31, 2018.

Copyright Notice

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

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   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Glossary  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  A note on satellite topology  . . . . . . . . . . . . . . . .   3
   3.  Status of network coding in actually deployed satellite
       systems . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Details on the use cases  . . . . . . . . . . . . . . . . . .   5
     4.1.  Two way relay channel mode  . . . . . . . . . . . . . . .   5
     4.2.  Reliable multi-cast . . . . . . . . . . . . . . . . . . .   6
     4.3.  Hybrid access . . . . . . . . . . . . . . . . . . . . . .   7
     4.4.  Delay Tolerant Network architecture . . . . . . . . . . .   7
     4.5.  Dealing with varying capacity . . . . . . . . . . . . . .   8
     4.6.  Improving the gateway handovers . . . . . . . . . . . . .   8
   5.  Discussion on the deployability . . . . . . . . . . . . . . .   9
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  10
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     10.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Network coding schemes are inherent part of the satellite systems as
   the physical layer requires specific robustness to guarantee an
   efficient usage of the expensive radio resource.  Further exploiting
   these schemes is an opportunity for a better end-user experience
   along with a better exploitation of the scarce resource.

   In this context, this memo aims at:

   o  summing up the current deployment of network coding schemes over
      LEO and GEO satellite systems;

   o  identifying opportunities for further usage of network coding in
      these systems.

1.1.  Glossary

   The glossary of this memo is related to the network coding taxonomy
   document [I-D.irtf-nwcrg-network-coding-taxonomy].

   The glossary is extended as follows:




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   o  BBFRAME: Base-Band FRAME;

   o  PLFRAME: Physical Layer FRAME;

   o  PEP: Performance Enhanced Proxy;

   o  SATCOM: SATellite COMmunications;

   o  EPC: Evolved Packet Core;

   o  UMTRAN: Universal Mobile Terrestrial Radio Access Network;

   o  QoS: Quality-of-Service;

   o  QoE: Quality-of-Experience;

   o  VNF: Virtualized Network Function;

   o  CPE: Customer Premise Equipment;

   o  ETSI: European Telecommunications Standards Institute;

   o  DTN: Delay Tolerant Network.

1.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  A note on satellite topology

   The objective of this section is to provide both a generic
   description of the components composing a generic satellite system
   and their interaction.  It provides a high level description of a
   multi-gateway satellites network.  There exist multiple SATCOM
   systems, such as those dedicated to broadcasting TV or to IoT
   applications: depending on the purpose of the SATCOM system, ground
   segments are specific.  This memo lays on SATCOM systems dedicated to
   Internet access that follows the DVB-S2/RCS2 standards.

   In this context, Figure 1 shows an example of a multigateway
   satellite system.  More details on a generic SATCOM ground segment
   architecture for a bi-directional Internet access can be found in
   [SAT2017].






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   It is worth noting that some functional blocks aggregate the traffic
   coming from multiple users, allowing the deployment of network coding
   schemes.

   +---------------------+
   | Application servers |
   +---------------------+
          |     |   |
          |     |   |
          -----------------------------------
          v     v   v             v   v     v
   +------------------+         +------------------+
   | network function |         | network function |
   | (firewall, PEP)  |         | (firewall, PEP)  |
   +------------------+         +------------------+
       |  |                        |        |
       |  | IP packets             |        |
       v  v                        v        v
   +------------------+         +------------------+
   | access gateway   |         | access gateway   |
   +------------------+         +------------------+
          |                                 |
          | BBFrames                        |
          v                                 v
   +------------------+         +------------------+
   | physical gateway |         | physical gateway |
   +------------------+         +------------------+
          |                                 |
          | PLFrames                        |
          v                                 v
   +------------------+         +------------------+
   | outdoor unit     |         | outdoor unit     |
   +------------------+         +------------------+
      |   |                         |       |
      |   | Satellite link          |       |
      v   v                         v       v
   +------------------+         +------------------+
   | sat terminals    |         | sat terminals    |
   +------------------+         +------------------+

    Figure 1: Data plane functions in a generic satellite multi-gateway
                                  system

3.  Status of network coding in actually deployed satellite systems

   Figure 2 presents the status of the network coding deployment in
   satellite systems.  The information is based on the taxonomy document
   [I-D.irtf-nwcrg-network-coding-taxonomy] and the notations are the



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   following: End-to-End Coding (E2E), Network Coding (NC), Intra-Flow
   Coding (IntraF), Inter-Flow Coding (InterF), Single-Path Coding (SP)
   and Multi-Path Coding (MP).

   X1 embodies the source coding that could be used at application level
   for instance: for video streaming on a broadband access.  X2 embodies
   the physical layer, applied to the PLFRAME, to optimize the satellite
   capacity usage.  Furthermore, at the physical layer and when random
   accesses are exploited, FEC mechanisms are exploited.

   +------+-------+---------+---------------+-------+
   |      | Upper | Middle  | Communication layers  |
   |      | Appl. | ware    |                       |
   +      +-------+---------+---------------+-------+
   |      |Source | Network | Packetization | PHY   |
   |      |coding | AL-FEC  | UDP/IP        | layer |
   +------+-------+---------+---------------+-------+
   |E2E   |   X1  |         |               |       |
   |NC    |       |         |               |       |
   |IntraF|   X1  |         |               |       |
   |InterF|       |         |               |   X2  |
   |SP    |   X1  |         |               |   X2  |
   |MP    |       |         |               |       |
   +------+-------+---------+---------------+-------+

              Figure 2: Network coding and satellite systems

4.  Details on the use cases

   This section details use-cases where network coding schemes could
   improve the overall performance of a SATCOM system (e.g. considering
   a more efficient usage of the satellite resource, delivery delay,
   delivery ratio).

   It is worth noting that these use-cases focus more on the middle ware
   (e.g. aggregation nodes) and packetization UDP/IP of Figure 2.
   Indeed, there are already lots of recovery mechanisms at the physical
   and access layers in currently deployed systems while E2E source
   coding are done at the application level.  In a multigateway SATCOM
   Internet access, the specific opportunities are more relevant in
   specific SATCOM components such as the "network function" block or
   the "access gateway" of Figure 1.

4.1.  Two way relay channel mode

   This use-case considers a two-way communication between end users,
   through a satellite link.  We propose an illustration of this
   scenario in Figure 3.



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   Satellite terminal A (resp.  B) transmits a flow A (resp.  B) to a
   server hosting NC capabilities, which forward a combination of the
   two flows to both terminals.  This results in non-negligible
   bandwidth saving and has been demonstrated at ASMS 2010 in Cagliari
   [ASMS2010].  Moreover, with On-Board Processing satellite payloads,
   the network coding operations could be done at the satellite level,
   thus reducing the end-to-end delay of the communication.

   +------------+        +-----+     +---------+
   | Satellite  |  A     |     | A   |         |
   | Terminal A |-->--|  |     |->---|         |  +------+
   +------------+     |  |     |->---|         |  |      |
       ||  A+B        ->-| SAT | B   | Gateway |  |      |
       ==================|     |     |         |--|Server|
       ||             ->-|     |     |         |  |      |
   +------------+  B  |>-|     |=====|         |  |      |
   | Satellite  |-->--|  |     | A+B |         |  +------+
   | Terminal B |        |     |     |         |
   +------------+        +-----+     +---------+

     Figure 3: Network architecture for two way relay channel with NC

4.2.  Reliable multi-cast

   This use-case considers adding redundancy to a multi-cast flow
   depending on what has been received by different end-users, resulting
   in non-negligible scarce resource saving.  We propose an illustration
   for this scenario in Figure 4.

   A multi-cast flow (M) is forward to both satellite terminals A and B.
   On the uplink, terminal A (resp.  B) does not acknowledge the packet
   Ni (resp.  Nj) and either the access gateway or the multi-cast server
   includes the missing packets in the multi-cast flow so that the
   information transfer is reliable.  This could be achieved by using
   NACK-Oriented Reliable Multicast (NORM) [RFC5740].  However, NORM
   does not consider other network coding schemes such as sliding window
   encoding described in [I-D.irtf-nwcrg-network-coding-taxonomy].














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   +------------+        +-----+       +---------+
   | Satellite  |NACK Ni |     |NACK Ni|         |
   | Terminal A |-->--|  |     |->-----|         |  +------+
   +------------+     |  |     |->-----|         |  |      |
       ||     M       ->-| SAT |NACK Nj|         |  |Multi |
       ==================|     |       | Gateway |--|Cast  |
       ||             ->-|     |       |         |  |Server|
   +------------+     |>-|     |=======|         |  |      |
   | Satellite  |-->--|  |     | M     |         |  +------+
   | Terminal B |NACK Nj |     |       |         |
   +------------+        +-----+       +---------+

     Figure 4: Network architecture for a reliable multi-cast with NC

4.3.  Hybrid access

   This use-case considers the use of multiple path management with
   network coding at the transport level to either increase the
   reliability or the total bandwidth.  We propose an illustration for
   this scenario in Figure 5.  This use-case is inspired from the
   Broadband Access via Integrated Terrestrial Satellite Systems (BATS)
   project and has been published as an ETSI Technical Report
   [ETSITR2017].  It is worth nothing that this kind of architecture is
   also discussed in the MPTCP working group [I-D.boucadair-mptcp-dhc].

   To cope from packet loss (due to either end-user movements or
   physical layer impairments), network coding could be introduced in
   both the CPE and at the concentrator.

                  +-------------+   +----------------+
               |->| SAT NETWORK |---| BACKBONE       |
               |  +-------------+   | +------------+ |
   +------+    |                    | |CONCENTRATOR| |
   | CPE  |-->-|  +-----+           | +------------+ |
   +------+    |->| DSL |-----------|                |
               |  +-----+           |                |
               |                    |                |
               |  +-----+           |                |
               |->| LTE |-----------|                |
                  +-----+           +----------------+

       Figure 5: Network architecture for an hybrid access using NC

4.4.  Delay Tolerant Network architecture

   ** EL: ** TBD with bundle layer as a candidate for NC





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4.5.  Dealing with varying capacity

   This use-case considers the usage of network coding to overcome cases
   where the wireless link characteristics quickly change overtime and
   where the physical layer codes could not be made robust in time.
   This is particularly relevant when end users are moving and the
   channel shows important variations [IEEEVT2001].

   The architecture is recalled in Figure 6.  The network coding schemes
   could be applied at the access gateway or the network function block
   levels to increase the reliability of the transmission.  This use-
   case is mostly relevant for when mobile users are considered or when
   the chosen band induce a required physical layer coding that may
   change over time (Q/V bands, Ka band, etc.).

   +------------+  +-----+  +---------+  +--------+  +---------+
   | Satellite  |  | SAT |  | Physical|  | Access |  | Network |
   | Terminal   |->|     |->| gateway |->| gateway|->| function|
   +------------+  +-----+  +---------+  +--------+  +---------+
        NC?                     NC           NC?         NC?

       Figure 6: Network architecture for dealing with varying link
                          characteristics with NC

4.6.  Improving the gateway handovers

   This use-case considers the recovery of packets that may be lost
   during gateway handovers.  Whether this is for off-loading one given
   equipment or because the transmission quality is not the same on each
   gateway, changing the transmission gateway may be relevant.  However,
   if gateways are not properly synchronized, this may result in packet
   loss.  During these critical phases, network coding can be added to
   improve the reliability of the transmission and propose a seamless
   gateway handover.

   An example architecture for this use-case is showed in Figure 7.  It
   is worth noting that depending on the ground architecture
   [I-D.chin-nfvrg-cloud-5g-core-structure-yang][SAT2017], some
   equipments might be communalised.












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                            +---------+  +--------+  +---------+
                            | Physical|  | Access |  | Network |
                      ----->| gateway |->| gateway|->| function|
                      |     +---------+  +--------+  +---------+
                      v                        |       |
   +------------+  +-----+                 +-------------+
   | Satellite  |  | SAT |                 | Switching   |
   | Terminal   |->|     |                 | Entity      |
   +------------+  +-----+                 +-------------+
                      ^                        |       |
                      |     +---------+  +--------+  +---------+
                      ----->| Physical|  | Access |  | Network |
                            | gateway |->| gateway|->| function|
                            +---------+  +--------+  +---------+

     Figure 7: Network architecture for dealing with gateway handover
                              schemes with NC

5.  Discussion on the deployability

   This section discusses the deployability of the use-cases detailed in
   Section 4.

   SATCOM systems typically feature Proxy-Enhanced-Proxy RFC 3135
   [RFC3135] which could be relevant to host network coding mechanisms
   and thus support the use-cases that have been discussed in Section 4.
   In particular the discussion on how network coding can be integrated
   inside a PEP with QoS scheduler has been proposed in RFC 5865
   [RFC5865].

   The generic architecture proposed in Figure 1 may be mapped to
   cellular networks as follows: the 'network function' block gather
   some of the functions of the Evolved Packet Core subsystem, while the
   'access gateway' and 'physical gateway' blocks gather the same type
   of functions as the Universal Mobile Terrestrial Radio Access
   Network.  This mapping extends the opportunities identified in this
   draft since they may be also relevant for cellular networks.

   Related to the foreseen virtualized network infrastructure, the
   network coding schemes could be proposed as VNF and their
   deployability enhanced.  The architecture for the next generation of
   SATCOM ground segments would rely on a virtualized environment.  This
   trend can also be seen, making the discussions on the deployability
   of network coding in SATCOM extendable to other deployment scenarios
   [I-D.chin-nfvrg-cloud-5g-core-structure-yang].  As one example, the
   network coding VNF functions deployment in a virtualized environment
   is presented in [I-D.vazquez-nfvrg-netcod-function-virtualization].




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6.  Acknowledgements

   Many thanks to Tomaso de Cola, Vincent Roca and Marie-Jose Montpetit.

7.  Contributors

   Tomaso de Cola, Vincent Roca, Marie-Jose Montpetit.

8.  IANA Considerations

   This memo includes no request to IANA.

9.  Security Considerations

   This document, by itself, presents no new privacy nor security
   issues.

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

   [ASMS2010]
              De Cola, T. and et. al., "Demonstration at opening session
              of ASMS 2010", ASMS , 2010.

   [ETSITR2017]
              "Satellite Earth Stations and Systems (SES); Multi-link
              routing scheme in hybrid access network with heterogeneous
              links", ETSI TR 103 351, 2017.

   [I-D.boucadair-mptcp-dhc]
              Boucadair, M., Jacquenet, C., and T. Reddy, "DHCP Options
              for Network-Assisted Multipath TCP (MPTCP)", draft-
              boucadair-mptcp-dhc-08 (work in progress), October 2017.

   [I-D.chin-nfvrg-cloud-5g-core-structure-yang]
              Chen, C. and Z. Pan, "Yang Data Model for Cloud Native 5G
              Core structure", draft-chin-nfvrg-cloud-5g-core-structure-
              yang-00 (work in progress), December 2017.





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   [I-D.irtf-nwcrg-network-coding-taxonomy]
              Adamson, B., Adjih, C., Bilbao, J., Firoiu, V., Fitzek,
              F., samah.ghanem@gmail.com, s., Lochin, E., Masucci, A.,
              Montpetit, M., Pedersen, M., Peralta, G., Roca, V.,
              Saxena, P., and S. Sivakumar, "Taxonomy of Coding
              Techniques for Efficient Network Communications", draft-
              irtf-nwcrg-network-coding-taxonomy-07 (work in progress),
              February 2018.

   [I-D.vazquez-nfvrg-netcod-function-virtualization]
              Vazquez-Castro, M., Do-Duy, T., Romano, S., and A. Tulino,
              "Network Coding Function Virtualization", draft-vazquez-
              nfvrg-netcod-function-virtualization-02 (work in
              progress), November 2017.

   [IEEEVT2001]
              Fontan, F., Vazquez-Castro, M., Cabado, C., Garcia, J.,
              and E. Kubista, "Statistical modeling of the LMS channel",
              IEEE Transactions on Vehicular Technology vol. 50 issue 6,
              2001.

   [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>.

   [RFC5740]  Adamson, B., Bormann, C., Handley, M., and J. Macker,
              "NACK-Oriented Reliable Multicast (NORM) Transport
              Protocol", RFC 5740, DOI 10.17487/RFC5740, November 2009,
              <https://www.rfc-editor.org/info/rfc5740>.

   [RFC5865]  Baker, F., Polk, J., and M. Dolly, "A Differentiated
              Services Code Point (DSCP) for Capacity-Admitted Traffic",
              RFC 5865, DOI 10.17487/RFC5865, May 2010,
              <https://www.rfc-editor.org/info/rfc5865>.

   [SAT2017]  Ahmed, T., Dubois, E., Dupe, JB., Ferrus, R., Gelard, P.,
              and N. Kuhn, "Software-defined satellite cloud RAN", Int.
              J. Satell. Commun. Network. vol. 36, 2017.

Authors' Addresses









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   Nicolas Kuhn (editor)
   CNES
   18 Avenue Edouard Belin
   Toulouse  31400
   France

   Email: nicolas.kuhn@cnes.fr


   Emmanuel Lochin (editor)
   ISAE-SUPAERO
   10 Avenue Edouard Belin
   Toulouse  31400
   France

   Email: emmanuel.lochin@isae-supaero.fr



































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