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Versions: (draft-kuhn-nwcrg-network-coding-satellites) 00 01 02 03 04 05 06

Internet Engineering Task Force                             N. Kuhn, Ed.
Internet-Draft                                                      CNES
Intended status: Informational                            E. Lochin, Ed.
Expires: February 20, 2020                                  ISAE-SUPAERO
                                                         August 19, 2019


                Coding techniques for satellite systems
             draft-irtf-nwcrg-network-coding-satellites-06

Abstract

   This document is the product of the Coding for Efficient Network
   Communications Research Group (NWCRG).  This document follows the
   taxonomy document [RFC8406] and considers coding as a linear
   combination of packets that operate in and above the network layer.
   In this context, this memo details a multi-gateway satellite system
   to identify use-cases where coding is relevant.  As example, coding
   operating in and above the network layer can be exploited to cope
   with residual losses or provide reliable multicast services.  The
   objective is to contribute to a larger deployment of such techniques
   in SATCOM systems.  This memo also identifies open research issues
   related to the deployment of coding in SATCOM systems, such as the
   interaction between congestion controls and coding techniques.

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
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   This Internet-Draft will expire on February 20, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   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
   carefully, as they describe your rights and restrictions with respect
   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.  A note on satellite topology  . . . . . . . . . . . . . . . .   5
   3.  Use-cases for improving the SATCOM system performance with
       coding techniques . . . . . . . . . . . . . . . . . . . . . .   8
     3.1.  Two-way relay channel mode  . . . . . . . . . . . . . . .   8
     3.2.  Reliable multicast  . . . . . . . . . . . . . . . . . . .   9
     3.3.  Hybrid access . . . . . . . . . . . . . . . . . . . . . .  10
     3.4.  Dealing with LAN losses . . . . . . . . . . . . . . . . .  10
     3.5.  Dealing with varying channel conditions . . . . . . . . .  11
     3.6.  Improving the gateway handovers . . . . . . . . . . . . .  12
   4.  Research challenges . . . . . . . . . . . . . . . . . . . . .  12
     4.1.  On the joint-use of coding techniques and congestion
           control in SATCOM systems . . . . . . . . . . . . . . . .  13
     4.2.  On the efficient usage of satellite resource  . . . . . .  13
     4.3.  Interaction with virtualized satellite gateways and
           terminals . . . . . . . . . . . . . . . . . . . . . . . .  13
     4.4.  Delay/Disruption Tolerant Networks  . . . . . . . . . . .  14
   5.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . .  14
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   9.  Informative References  . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

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 adds to cope with link impairments, without
   reducing the goodput when the channel quality is good.  There is
   usually enough redundancy to guarantee a Quasi-Error Free
   transmission.  The recovery time depends on the encoding block size.
   Considering for instance geostationary satellite system (GEO),
   physical or link layer erasure coding mechanisms recover transmission
   losses within a negligible delay compared to link delay.  However,



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   when retransmissions are triggered, this leads to a non-negligible
   additional delay in particular over GEO link.  Further exploiting
   coding techniques at application or transport layers is an
   opportunity for releasing constraints on the physical layer and
   improving the performance of SATCOM systems.

   The notations used in this document are based on the taxonomy
   document [RFC8406]:

   o  Channel and link codings are gathered in the PHY layer coding and
      are out of the scope of this document.

   o  FEC (also called Application-Level FEC) operates in and above the
      network layer.

   o  This document considers coding (or coding techniques or coding
      schemes) as a linear combination and not as a content coding
      (e.g., to compress a video flow).

   Figure 1 presents the status of the reliability schemes deployment in
   satellite systems.

   o  X1 embodies the source coding techniques that could be used at
      application level for instance within QUIC.  This is not specific
      to SATCOM systems since such deployment can be relevant for
      broadband Internet access discussions.

   o  X2 embodies the physical-layer techniques exploited in SATCOM
      systems (note that other coding techniques can be exploited).
      This is out of the scope of the document.

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

        Figure 1: Reliability schemes in current satellite systems




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   We notice an active research activity on coding techniques and
   SATCOM.  That being said, not much has actually made it to industrial
   developments.  In this context, this document aims at identifying
   opportunities for further usage of coding in these systems.

   The glossary of this memo extends the glossary of the taxonomy
   document [RFC8406] as follows:

   o  ACM : Adaptive Coding and Modulation;

   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 Premises Equipment;

   o  COM: COMmunication;

   o  DSL: Digital Subscriber Line;

   o  DTN: Delay/Disruption Tolerant Network;

   o  DVB: Digital Video Broadcasting;

   o  E2E: End-to-end;

   o  ETSI: European Telecommunications Standards Institute;

   o  FEC: Forward Error Correction;

   o  FLUTE: File Delivery over Unidirectional Transport;

   o  IntraF: Intra-Flow Coding;

   o  InterF: Inter-Flow Coding;

   o  IoT: Internet of Things;

   o  LTE: Long Term Evolution;

   o  MPC: Multi-Path Coding;

   o  NC: Network Coding;

   o  NFV: Network Function Virtualization;



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   o  NORM: NACK-Oriented Reliable Multicast;

   o  PEP: Performance Enhancing Proxy [RFC3135] - 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  QEF: Quasi-Error-Free;

   o  QoE: Quality-of-Experience;

   o  QoS: Quality-of-Service;

   o  SAT: SATellite;

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

   o  SPC: Single-Path Coding;

   o  VNF: Virtual Network Function.

   This document is the product of and represents the collaborative work
   and consensus of the Coding for Efficient Network Communications
   Research Group (NWCRG); it is not an IETF product and is not a
   standard.

2.  A note on satellite topology

   This section describes a satellite system that follows the ETSI DVB
   standards to provide broadband Internet access.  A high-level
   description of a multi-gateway satellite network is provided.  There
   are 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.  In this context, the increase
   of the available capacity that is carried out to end users and
   reliability requirements lead to multiple gateways for one unique
   satellite platform.

   In this context, Figure 2 shows an example of a multi-gateway
   satellite system.  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 discussions and a generic SATCOM ground segment architecture
   for bidirectional Internet access can be found in [SAT2017].




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   Some functional blocks aggregate the traffic of multiple users.


















































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   +--------------------------+
   | application servers      |
   | (data, coding, multicast |
   +--------------------------+
          ^     ^
          | ... |
          -----------------------------------
          v     v   v             v   v     v
   +------------------+         +------------------+
   | network function |         | network function |
   | (firewall, PEP)  |         | (firewall, PEP)  |
   +------------------+         +------------------+
       ^     ^                        ^        ^
       | ... | IP packets             |  ...   |
       v     v                        v        v   ---
   +------------------+         +------------------+ |
   | access gateway   |         | access gateway   | |
   +------------------+         +------------------+ |
          ^                                 ^        |
          | BBFRAME                         |        | gateway
          v                                 v        |
   +------------------+         +------------------+ |
   | physical gateway |         | physical gateway | |
   +------------------+         +------------------+ |
          ^                                 ^      ---
          | PLFRAME                         |
          v                                 v
   +------------------+         +------------------+
   | outdoor unit     |         | outdoor unit     |
   +------------------+         +------------------+
          ^                                 ^
          | satellite link                  |
          v                                 v
   +------------------+         +------------------+
   | sat terminals    |         | sat terminals    |
   +------------------+         +------------------+
          ^        ^                  ^        ^
          |        |                  |        |
          v        |                  v        |
   +----------+    |             +----------+  |
   | end user |    |             | end user |  |
   +----------+    v            +----------+  v
   +------------------+         +------------------+
   | end user         |         | end user         |
   +------------------+         +------------------+

    Figure 2: Data plane functions in a generic satellite multi-gateway
                                  system



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3.  Use-cases for improving the SATCOM system performance with coding
    techniques

   This section details use-cases where coding techniques could provide
   interesting features for SATCOM systems.  Combination of the
   presented use-cases could also be relevant.

   It is worth noting that these use-cases mostly focus on the
   middleware and packetization UDP/IP of Figure 1.  There are already
   lots of recovery mechanisms at the physical-layer in currently
   deployed systems while E2E source coding is done at the application
   level.  In a multi-gateway SATCOM Internet access, the deployment
   opportunities are more relevant in specific SATCOM components such as
   the "network function" block or the "access gateway" of Figure 2.

3.1.  Two-way relay channel mode

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

   Satellite terminal A sends a flow A and satellite terminal B sends a
   flow B to a coding server.  The coding server sends a combination of
   both terminal flows.  This results in non-negligible capacity savings
   and has been demonstrated [ASMS2010].  In the proposed example, a
   dedicated coding server is introduced.  Its location could be changed
   depending on the deployment use-case.  With On-Board Processing
   satellite payloads, the coding operations could be done at the
   satellite level; although this would require lots of computational
   ressource on-board and may not be relevant with today's payloads.

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

   +-----------+        +-----+
   |Sat term A |--A}-+  |     |
   +-----------+     |  |     |      +---------+      +------+
       ^^            +--|     |--A}--|         |--A}--|Coding|
       ||               | 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



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3.2.  Reliable multicast

   Using multicast servers is a way to better exploit the satellite
   broadcast capabilities.  This approach is proposed in the SHINE ESA
   project [I-D.vazquez-nfvrg-netcod-function-virtualization] [SHINE].
   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.

   -Li}- : packet indicating the loss of packet i of a multicast flow M
   ={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

   A multicast flow (M) is forwarded to both satellite terminals A and
   B.  However packet Ni (resp.  Nj) gets lost at terminal A (resp.  B),
   and terminal A (resp.  B) returns a negative acknowledgment 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 to let both
   terminals recover from losses.

   This could be achieved by using other multicast or broadcast systems,
   such as NACK-Oriented Reliable Multicast (NORM) [RFC5740] or File
   Delivery over Unidirectional Transport (FLUTE) [RFC6726].  Note that
   both NORM and FLUTE are limited to block coding, none of them
   supporting sliding window encoding schemes [RFC8406].  Note that
   although FLUTE is defined as an unidirectional protocol, the RFC
   proposes a bidirectional communication method to enable full
   reliability transfer and for security purposes.








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3.3.  Hybrid access

   This use-case considers the use of multiple path management with
   coding at the transport layer to increase the reliability and/or the
   total capacity (using multiple paths does not guarantee an
   improvement of both the reliability and the total capacity).  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].  This kind of architecture is also
   discussed in the TCPM working group [I-D.ietf-tcpm-converters].

   To cope with packet loss (due to either end-user mobility or
   physical-layer impairments), coding techniques could be introduced
   both at the CPE and at the concentrator.  Apart from packet losses,
   other gains could be envisioned, such as a better tolerance to out-
   of-order packets which occur when exploited links exhibit high
   asymetry in terms of RTT.  Depending on the ground architecture
   [I-D.chin-nfvrg-cloud-5g-core-structure-yang] [SAT2017], some
   equipments might be hosting both SATCOM and cellular functions.

-{}- : bidirectional link

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

     Figure 5: Network architecture for an hybrid access using coding

3.4.  Dealing with LAN losses

   This use-case considers the usage of coding techniques to cope with
   cases where the end user connects to the satellite terminal with a
   Wi-Fi link that exhibits losses.  In the case of encrypted end-to-end
   applications based on UDP, PEP cannot operate.  The Wi-Fi losses
   result in an end-to-end retransmission that would harm the quality of
   experience of the end user.

   The architecture is recalled in Figure 6.




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   In this use-case, adding coding techniques could prevent the end-to-
   end retransmission from occuring.

-{}- : bidirectional link
-''- : Wi-Fi link
C : where coding techniques could be introduced

+---------+    +---------+    +---+    +--------+    +-------+    +--------+
|         |    |Satellite|    |SAT|    |Physical|    |Access |    |Network |
|End user |-''-|Terminal |-{}-|   |-{}-|Gateway |-{}-|Gateway|-{}-|Function|
+---------+    +---------+    +---+    +--------+    +-------+    +--------+
     C                       C            C           C

        Figure 6: Network architecture for dealing with LAN losses

3.5.  Dealing with varying channel conditions

   This use-case considers the usage of coding techniques to cope with
   cases where channel condition can change in less than a second and
   where the physical-layer codes could not efficiently guarantee a
   Quasi-Error-Free (QEF) transmission.

   The architecture is recalled in Figure 7.  In these cases, the
   mechanisms that are exploited to adapt the physical-layer codes
   (Adaptative Coding and Modulation (ACM)) may adapt the modulation and
   coding in time: remaining errors could be recovered with higher layer
   redundancy packets.  Coding may be applied on IP packets or on
   layer-2 proprietary format packets.

   This use-case is mostly relevant when mobile users are considered or
   when the chosen band induces 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 coding techniques is
   different.

   -{}- : bidirectional link
   C : where coding techniques could be introduced

   +---------+    +---+    +--------+    +-------+    +--------+
   |Satellite|    |SAT|    |Physical|    |Access |    |Network |
   |Terminal |-{}-|   |-{}-|Gateway |-{}-|Gateway|-{}-|Function|
   +---------+    +---+    +--------+    +-------+    +--------+
        C                       C            C           C

       Figure 7: Network architecture for dealing with varying link
                              characteristics



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3.6.  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 or if the algorithm that is
   exploited to trigger gateway handovers shows a non negligible
   probability of missed detection, this may result in packet losses.
   During these critical phases, coding can be added to improve the
   reliability of the transmission and allow a seamless gateway
   handover.  Coding could be applied at either the access gateway or
   the network function block.  A potential control plane is in charge
   of taking the decision to change the communication gateway and the
   consequent routes.

   Figure 8 illustrates this use-case.

   -{}- : bidirectional link
   !   : management interface
   C : where coding techniques could be introduced
                                           C             C
                         +--------+    +-------+    +--------+
                         |Physical|    |Access |    |Network |
                    +-{}-|gateway |-{}-|gateway|-{}-|function|
                    |    +--------+    +-------+    +--------+
                    |                        !       !
   +---------+    +---+              +---------------+
   |Satellite|    |SAT|              | Control plane |
   |Terminal |-{}-|   |              | manager       |
   +---------+    +---+              +---------------+
                    |                        !       !
                    |    +--------+    +-------+    +--------+
                    +-{}-|Physical|-{}-|Access |-{}-|Network |
                         |gateway |    |gateway|    |function|
                         +--------+    +-------+    +--------+
                                           C             C

     Figure 8: Network architecture for dealing with gateway handover
                                  schemes

4.  Research challenges

   This section proposes a few potential approaches to introduce and use
   coding techniques in SATCOM systems.






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4.1.  On the joint-use of coding techniques and congestion control in
      SATCOM systems

   SATCOM systems typically feature Performance Enhancement Proxy (PEP)
   RFC 3135 [RFC3135].  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.  PEP contributes to mitigate
   congestion in a SATCOM systems.  PEP could host coding mechanisms and
   thus support use-cases that have been discussed in this document.

   Deploying coding schemes at the TCP level in these equipment could be
   relevant and independent from the specific characteristics of a
   SATCOM link.  This leads to research questions on the interaction
   between coding schemes and TCP congestion controls.

4.2.  On the efficient usage of satellite resource

   The recurrent trade-off in SATCOM systems remains: how much overhead
   from redundant reliability packets can be introduced to guarantee a
   better end-user QoE while optimizing capacity usage ? At which layer
   this supplementary coding could be added ?

   This problem has been tackled in the past for physical-layer code,
   but there remains questions on how to adapt the overhead for, e.g.,
   the quickly varying channel conditions use-case.

4.3.  Interaction with virtualized satellite gateways and terminals

   Related to the foreseen virtualized network infrastructure, coding
   techniques could be easily deployed as VNF.  Next generation of
   SATCOM ground segments could rely on a virtualized environment.  This
   trend can also be seen in cellular networks, making these discussions
   extendable to other deployment scenarios
   [I-D.chin-nfvrg-cloud-5g-core-structure-yang].  As one example, the
   coding VNF 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 efficient radio usage and
   easy-to-deploy SATCOM services.  Moreover, another challenge related
   to a virtualized SATCOM equipment is the management of limited
   buffered capacities.








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4.4.  Delay/Disruption Tolerant Networks

   Communications among deep-space platforms and terrestrial gateways
   can be a challenge.  Reliable end-to-end (E2E) communications over
   such paths must cope with long delay and frequent link disruptions;
   indeed, contemporaneous E2E connectivity may be available only
   intermittently or never.  Delay/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.  Moreover, DTN can also be seen as an
   alternative solution to transfer the data between a central PEP and a
   remote PEP.

   Coding enables E2E reliable communication over DTN with adaptive re-
   encoding, as proposed in [THAI15].  In this case, the use-cases
   proposed in Section 3.5 would legitimize the usage of coding within
   the DTN stack to improve the channel utilization and the E2E
   transmission delay.  In this context, the use of erasure coding
   techniques inside a Consultative Committee for Space Data Systems
   (CCSDS) architecture has been specified in [CCSDS-131.5-O-1].  A
   research challenge would be on how such coding can be integrated in
   the IETF DTN stack.

5.  Conclusion

   This document discuses some opportunities to introduce coding
   techniques at a wider scale in satellite telecommunications systems.

   Even though this document focuses on satellite systems, it is worth
   pointing out that some scenarios proposed may be relevant to other
   wireless telecommunication systems.  As one example, the generic
   architecture proposed in Figure 2 may be mapped to cellular networks
   as follows: the 'network function' block gathers 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.

6.  Acknowledgements

   Many thanks to John Border, Stuart Card, Tomaso de Cola, Vincent
   Roca, Lloyd Wood and Marie-Jose Montpetit for their help in writing
   this document.







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7.  IANA Considerations

   This memo includes no request to IANA.

8.  Security Considerations

   Security considerations are inherent to any access network, and in
   particular SATCOM systems.  The use of FEC or Network Coding in
   SATCOM also comes with risks (e.g., a single corrupted redundant
   packet may propagate to several flows when they are protected
   together in an Inter-Flow coding approach, see section Section 3).
   However this is not specific to the SATCOM use-case and this document
   does not further elaborate on it.

9.  Informative References

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

   [CCSDS-131.5-O-1]
              "Erasure correcting codes for use in near-earth and deep-
              space communications", CCSDS Experimental
              specification 131.5-0-1, 2014.

   [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.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.ietf-tcpm-converters]
              Bonaventure, O., Boucadair, M., Gundavelli, S., Seo, S.,
              and B. Hesmans, "0-RTT TCP Convert Protocol", draft-ietf-
              tcpm-converters-10 (work in progress), August 2019.

   [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.






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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>.

   [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>.

   [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>.

   [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.

   [SHINE]    Pietro Romano, S. and et. al., "Secure Hybrid In Network
              caching Environment (SHINE) ESA project", ESA project ,
              2017 on-going.

   [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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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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