Network coding and satellites
draft-irtf-nwcrg-network-coding-satellites-00

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Internet Engineering Task Force                             N. Kuhn, Ed.
Internet-Draft                                                      CNES
Intended status: Informational                            E. Lochin, Ed.
Expires: April 8, 2019                                      ISAE-SUPAERO
                                                             Oct 5, 2018

                     Network coding and satellites
             draft-irtf-nwcrg-network-coding-satellites-00

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.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Glossary  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  A note on satellite topology  . . . . . . . . . . . . . . . .   4
   3.  Status of network coding in actually deployed satellite
       systems . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Details on the use cases  . . . . . . . . . . . . . . . . . .   6
     4.1.  Two way relay channel mode  . . . . . . . . . . . . . . .   7
     4.2.  Reliable multicast  . . . . . . . . . . . . . . . . . . .   7
     4.3.  Hybrid access . . . . . . . . . . . . . . . . . . . . . .   8
     4.4.  Dealing with varying capacity . . . . . . . . . . . . . .   9
     4.5.  Improving the gateway handovers . . . . . . . . . . . . .  10
     4.6.  Delay/Disruption Tolerant Networks  . . . . . . . . . . .  10
   5.  Research challenges . . . . . . . . . . . . . . . . . . . . .  11
     5.1.  Deployability in current SATCOM systems . . . . . . . . .  11
     5.2.  Interaction with NFV  . . . . . . . . . . . . . . . . . .  12
   6.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . .  12
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  12
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  13
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     11.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   Guaranteeing both physical layer robustness and efficient usage of
   the radio resource has been in the core design of SATellite
   COMmunication (SATCOM) systems.  The trade-off often resided in how
   much redundancy a system had to add to cope from link impairments,
   without reducing the good-put when the channel quality is high.
   Generally speaking, enough redundancy is added so as to guarantee a
   Quasi-Error Free transmission; however, there are cases where the
   physical layer could hardly recover the transmission losses (e.g.
   with a mobile user) and layer 2 (or above) re-transmissions induce an
   at least 500 ms delay with a geostationary satellite.  Further
   exploiting network coding schemes at higher OSI-layers is an
   opportunity for releasing constraints on the physical layer and
   improving the performance of SATCOM systems when the physical layer
   is challenged.  We have noticed an active research activity on how
   network coding and SATCOM in the past.  That being said, not much has
   actually made it to industrial developments.  In this context, this
   memo aims at:

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   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 [RFC8406].

   The glossary is extended as follows:

   o  BBFRAME: Base-Band FRAME - satellite communication layer 2
      encapsulation work as follows: (1) each layer 3 packet is
      encapsulated with a Generic Stream Encapsulation (GSE) mechanism,
      (2) GSE packets are gathered to create BBFRAMEs, (3) BBFRAMEs
      contain information related to how they have to be modulated (4)
      BBFRAMEs are forwarded to the physical layer;

   o  CPE: Customer Premise Equipment;

   o  DTN: Delay/Disruption Tolerant Network;

   o  EPC: Evolved Packet Core;

   o  ETSI: European Telecommunications Standards Institute;

   o  PEP: Performance Enhanced Proxy - a typical PEP for satellite
      communications include compression, caching and TCP acceleration;

   o  PLFRAME: Physical Layer FRAME - modulated version of a BBFRAME
      with additional information (e.g. related to synchronization);

   o  SATCOM: generic term related to all kind of SATellite
      COMmunications systems;

   o  QoS: Quality-of-Service;

   o  QoE: Quality-of-Experience;

   o  VNF: Virtualized Network Function.

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].

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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, the increase of the available capacity that is carried out
   to end users and the need for reliability results in the need for
   multiple gateways for one unique satellite platform.

   In this context, Figure 1 shows an example of a multi-gateway
   satellite system.  More details on a generic SATCOM ground segment
   architecture for a bi-directional Internet access can be found in
   [SAT2017].  We propose a multi-gateway system since some of the use-
   cases described in this document require multiple gateways.  In a
   multi-gateway system, some elements may be centralized and/or
   gathered: the relevance of one approach compared to another depends
   on the deployment scenario.  More information on these trade-off
   discussions can be found in [SAT2017].

   It is worth noting that some functional blocks aggregate the traffic
   coming from multiple users.  Even if network coding schemes could be
   applied to any individual traffic, it could also work on an
   aggregate.

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   +---------------------+
   | 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
   +------------------+         +------------------+
   | sat terminals    |         | sat terminals    |
   +------------------+         +------------------+
          ^                                 ^
          |                                 |
          v                                 v
   +------------------+         +------------------+
   | end user         |         | end user         |
   +------------------+         +------------------+

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

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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
   [RFC8406] and the notations are the 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.  It is worth
   pointing out that NC is an inherent part of the physical layer of
   satellite systems, but based on public information, NC does not seem
   to be widely used at higher OSI layers.

   +------+-------+---------+---------------+-------+
   |      | 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 in current 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 middleware
   (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 multi-gateway SATCOM
   Internet access, the specific opportunities are more relevant in

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   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.

   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.

   -X}-   : traffic from satellite terminal X to the server
   ={X+Y= : traffic from X and Y combined transmitted from
               the server to terminals X and Y

   +-----------+        +-----+
   |Sat term A |--A}-+  |     |
   +-----------+     |  |     |      +---------+      +------+
       ^^            +--|     |--A}--|         |--A}--|      |
       ||               | SAT |--B}--| Gateway |--B}--|Server|
       ===={A+B=========|     |={A+B=|         |={A+B=|      |
       ||               |     |      +---------+      +------+
       vv            +--|     |
   +-----------+     |  |     |
   |Sat term B |--B}-+  |     |
   +-----------+        +-----+

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

4.2.  Reliable multicast

   This use-case considers adding redundancy to a multicast 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 multicast flow (M) is forwarded to both satellite terminals A and
   B.  However packet Ni (resp.  Nj) get lost at terminal A (resp.  B),
   and terminal A (resp.  B) returns a negative acknowledgement Li
   (resp.  Lj), indicating that the packet is missing.  Then either the
   access gateway or the multicast server includes a repair packet
   (rather than the individual Ni and Nj packets) in the multicast flow

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   to let both terminals recover from losses.  This could be achieved by
   using NACK-Oriented Reliable Multicast (NORM) [RFC5740] in situations
   where a feedback is possible and desirable, or FLUTE/ALC [RFC6726]
   when it is not the case.  Note that currently both NORM nor FLUTE/ALC
   are limited to block coding, none of them supporting sliding window
   encoding schemes [RFC8406].

   -Li}- : packet indicated the loss of packet i of a multicast flow
   ={M== : multicast flow including the missing packets

   +-----------+       +-----+
   |Sat term A |-Li}-+ |     |
   +-----------+     | |     |      +---------+  +------+
       ^^            +-|     |-Li}--|         |  |Multi |
       ||              | SAT |-Lj}--| Gateway |--|Cast  |
       ===={M==========|     |={M===|         |  |Server|
       ||              |     |      +---------+  +------+
       vv            +-|     |
   +-----------+     | |     |
   |Sat term B |-Lj}-+ |     |
   +-----------+       +-----+

      Figure 4: Network architecture for a reliable multicast with NC

4.3.  Hybrid access

   This use-case considers the use of multiple path management with
   network coding at the transport level to increase the reliability
   and/or the total bandwidth (using multiple path does not guarantee an
   improvement of both the reliability and 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 with packet loss (due to either end-user mobility or physical
   layer impairments), network coding could be introduced in both the
   CPE and at the concentrator.

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  -{}- : bidirectional link

                               +-----+    +----------------+
                          +-{}-| SAT |-{}-| BACKBONE       |
  +------+    +------+    |    +-----+    | +------------+ |
  | End  |-{}-| CPE  |-{}-|               | |CONCENTRATOR| |
  | User |    |      |    |    +-----+    | +------------+ |    +------+
  +------+    +------+    |-{}-| DSL |-{}-|                |-{}-|Data  |
                          |    +-----+    |                |    |Server|
                          |               |                |    +------+
                          |    +-----+    |                |
                          +-{}-| LTE |-{}-|                |
                               +-----+    +----------------+

       Figure 5: Network architecture for an hybrid access using NC

4.4.  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.).  Depending on the use-
   case (e.g. very high frequency bands, mobile users) or depending on
   the deployment use-cases (e.g. performance of the network between
   each individual block), the relevance of adding network coding is
   different.  Then, depending on the OSI level at which network coding
   is applied, the impact on the satellite terminal is different:
   network coding may be applied on IP packets or on layer-2 proprietary
   format packets.

   -{}- : bidirectional link

   +---------+    +---+    +--------+    +-------+    +--------+
   |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

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4.5.  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.  In this case, the network coding could be applied
   at either the access gateway or the network function block.  The
   entity responsible for taking the decision to change the
   communication gateway and changing the routes is the control plane
   manager; this entity exploits a management interface.

   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
   equipment might be communalised.

   -{}- : bidirectional link
   !   : management interface
                                          NC            NC
                         +--------+    +-------+    +--------+
                         |Physical|    |Access |    |Network |
                    +-{}-|gateway |-{}-|gateway|-{}-|function|
                    |    +--------+    +-------+    +--------+
                    |                        !       !
   +---------+    +---+              +---------------+
   |Satellite|    |SAT|              | Control plane |
   |Terminal |-{}-|   |              | manager       |
   +---------+    +---+              +---------------+
                    |                        !       !
                    |    +--------+    +-------+    +--------+
                    +-{}-|Physical|-{}-|Access |-{}-|Network |
                         |gateway |    |gateway|    |function|
                         +--------+    +-------+    +--------+
                                          NC            NC

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

4.6.  Delay/Disruption Tolerant Networks

   Establishing communications from terrestrial gateways to aerospace
   components is a challenge due to the distances involved.  As a matter
   of fact, reliable end-to-end (E2E) communications over such links
   must cope with long delay and frequent link disruptions.  Delay/

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   Disruption Tolerant Networking [RFC4838] is a solution to enable
   reliable internetworking space communications where both standard ad-
   hoc routing and E2E Internet protocols cannot be used.  DTN can also
   be seen as an alternative solution to cope with satellite
   communications usually managed by PEP.  Therefore, the transport of
   data over such networks requires the use of replication, erasure
   codes and multipath protocol schemes [WANG05] [ZHANG06] to improve
   the bundle delivery ratio and/or delivery delay.  For instance,
   transport protocols such as LTP [RFC5326] for long delay links with
   connectivity disruptions, use Automatic Repeat-reQuest (ARQ) and
   unequal error protection to reduce the amount of non-mandatory re-
   transmissions.  The work in [TOURNOUX10] proposed upon LTP a robust
   streaming method based on an on-the-fly coding scheme, where encoding
   and decoding procedures are done at the source and destination nodes,
   respectively.  However, each link path loss rate may have various
   order of magnitude and re-encoding at an intermediate node to adapt
   the redundancy can be mandatory to prevent transmission wasting.
   This idea has been put forward in
   [I-D.zinky-dtnrg-random-binary-fec-scheme] and
   [I-D.zinky-dtnrg-erasure-coding-extension], where the authors
   proposed an encoding process at intermediate DTN nodes to explore the
   possibilities of Forward Error Correction (FEC) schemes inside the
   bundle protocol [RFC5050].  Another proposal is the use of erasure
   coding inside the CCSDS (Consultative Committee for Space Data
   Systems) architecture [COLA11].  The objective is to extend the CCSDS
   File Delivery Protocol (CFDP) [CCSDS-FDP] with erasure coding
   capabilities where a Low Density Parity Check (LDPC) [RFC6816] code
   with a large block size is chosen.  Recently, on-the-fly erasure
   coding schemes [LACAN08] [SUNDARARAJAN08] [TOURNOUX11] have shown
   their benefits in terms of recovery capability and configuration
   complexity compared to traditional FEC schemes.  Using a feedback
   path when available, on-the-fly schemes can be used to enable E2E
   reliable communication over DTN with adaptive re-encoding as proposed
   in [THAI15].

5.  Research challenges

5.1.  Deployability in current SATCOM systems

   SATCOM systems typically feature Performance Enhancement 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.  PEP usually split TCP end-to-end connections and forward
   TCP packets to the satellite baseband gateway that deals with layer 2
   and layer 1 encapsulations.  Deploying network coding schemes at the
   TCP level in these equipments could be relevant and independant from
   the specificities of a SATCOM link.  That being said, we can notice a
   research issue in the recurrent trade-off in SATCOM systems that is

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   related to the amount of reliability that you introduce in the first
   transmission to guarantee a better end-user QoE and the usage of the
   scarce resource.

5.2.  Interaction with NFV

   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].
   A research challenge would be the optimization of the NFV service
   function chaining, considering a virtualized infrastructure and other
   SATCOM specific functions, to guarantee an efficient radio resource
   utilization and easy to deploy SATCOM services.

6.  Conclusion

   This document presents 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.

   Even if this document focuses on satellite systems, it is worth
   pointing out that the some scenarios proposed may be relevant to
   other wireless telecommunication systems.  As one example, 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.

7.  Acknowledgements

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

8.  Contributors

   Tomaso de Cola, Marie-Jose Montpetit.

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9.  IANA Considerations

   This memo includes no request to IANA.

10.  Security Considerations

   Security considerations are inherent to any access network.  SATCOM
   systems introduce standard security mechanisms.  In particular, there
   are some specificities related to the fact that all users under the
   coverage can record all the packets that are being transmitted, such
   as in LTE networks.  On the specific scenario of NC in SATCOM
   systems, there are no specific security considerations.

11.  References

11.1.  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>.

11.2.  Informative References

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

   [CCSDS-FDP]
              "CCSDS File Delivery Protocol, Recommendation for Space
              Data System Standards", CCSDS 727.0-B-4, Blue Book num. 3,
              2007.

   [COLA11]   De Cola, T., Paolini, E., Liva, G., and G. Calzolari,
              "Reliability options for data communications in the future
              deep-space missions", Proceedings of the IEEE vol. 99
              issue 11, 2011.

   [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.

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Internet-Draft        Network coding and satellites             Oct 2018

   [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.

   [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.

   [I-D.zinky-dtnrg-erasure-coding-extension]
              Zinky, J., Caro, A., and G. Stein, "Bundle Protocol
              Erasure Coding Extension", draft-zinky-dtnrg-erasure-
              coding-extension-00 (work in progress), August 2012.

   [I-D.zinky-dtnrg-random-binary-fec-scheme]
              Zinky, J., Caro, A., and G. Stein, "Random Binary FEC
              Scheme for Bundle Protocol", draft-zinky-dtnrg-random-
              binary-fec-scheme-00 (work in progress), August 2012.

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

   [LACAN08]  Lacan, J. and E. Lochin, "Rethinking reliability for long-
              delay networks", International Workshop on Satellite and
              Space Communications , October 2008.

   [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>.

   [RFC4838]  Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst,
              R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant
              Networking Architecture", RFC 4838, DOI 10.17487/RFC4838,
              April 2007, <https://www.rfc-editor.org/info/rfc4838>.

   [RFC5050]  Scott, K. and S. Burleigh, "Bundle Protocol
              Specification", RFC 5050, DOI 10.17487/RFC5050, November
              2007, <https://www.rfc-editor.org/info/rfc5050>.

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   [RFC5326]  Ramadas, M., Burleigh, S., and S. Farrell, "Licklider
              Transmission Protocol - Specification", RFC 5326,
              DOI 10.17487/RFC5326, September 2008,
              <https://www.rfc-editor.org/info/rfc5326>.

   [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>.

   [RFC6726]  Paila, T., Walsh, R., Luby, M., Roca, V., and R. Lehtonen,
              "FLUTE - File Delivery over Unidirectional Transport",
              RFC 6726, DOI 10.17487/RFC6726, November 2012,
              <https://www.rfc-editor.org/info/rfc6726>.

   [RFC6816]  Roca, V., Cunche, M., and J. Lacan, "Simple Low-Density
              Parity Check (LDPC) Staircase Forward Error Correction
              (FEC) Scheme for FECFRAME", RFC 6816,
              DOI 10.17487/RFC6816, December 2012,
              <https://www.rfc-editor.org/info/rfc6816>.

   [RFC8406]  Adamson, B., Adjih, C., Bilbao, J., Firoiu, V., Fitzek,
              F., Ghanem, S., Lochin, E., Masucci, A., Montpetit, M-J.,
              Pedersen, M., Peralta, G., Roca, V., Ed., Saxena, P., and
              S. Sivakumar, "Taxonomy of Coding Techniques for Efficient
              Network Communications", RFC 8406, DOI 10.17487/RFC8406,
              June 2018, <https://www.rfc-editor.org/info/rfc8406>.

   [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.

   [SUNDARARAJAN08]
              Sundararajan, J., Shah, D., and M. Medard, "ARQ for
              network coding", IEEE Int. Symp. on Information Theory ,
              July 2008.

   [THAI15]   Thai, T., Chaganti, V., Lochin, E., Lacan, J., Dubois, E.,
              and P. Gelard, "Enabling E2E reliable communications with
              adaptive re-encoding over delay tolerant networks",
              Proceedings of the IEEE International Conference on
              Communications , June 2015.

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   [TOURNOUX10]
              Tournoux, P., Lochin, E., Leguay, J., and J. Lacan, "On
              the benefits of random linear coding for unicast
              applications in disruption tolerant networks", Proceedings
              of the IEEE International Conference on Communications ,
              2010.

   [TOURNOUX11]
              Tournoux, P., Lochin, E., Lacan, J., Bouabdallah, A., and
              V. Roca, "On-the-fly erasure coding for real-time video
              applications", IEEE Trans. on Multimedia vol. 13 issue 4,
              August 2011.

   [WANG05]   Wang, Y. and et. al., "Erasure-coding based routing for
              opportunistic networks", Proceedings of the ACM SIGCOMM
              workshop on Delay-tolerant networking , 2005.

   [ZHANG06]  Zhang, X. and et. al., "On the benefits of random linear
              coding for unicast applications in disruption tolerant
              networks", Proceedings of the 4th International Symposium
              on Modeling and Optimization in Mobile, Ad Hoc and
              Wireless Networks , 2006.

Authors' Addresses

   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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