Internet Engineering Task Force N. Kuhn, Ed.
Internet-Draft CNES
Intended status: Informational E. Lochin, Ed.
Expires: August 29, 2018 ISAE-SUPAERO
February 25, 2018
Network coding and satellites
draft-kuhn-nwcrg-network-coding-satellites-02
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 . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. A note on satellite topology . . . . . . . . . . . . . . . . 3
3. Status of network coding in actually deployed satellite
systems . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Opportunities for more network coding in satellite systems . 5
5. Details on the use cases . . . . . . . . . . . . . . . . . . 6
5.1. Two way relay channel mode . . . . . . . . . . . . . . . 6
5.2. Reliable multi-cast . . . . . . . . . . . . . . . . . . . 7
5.3. Hybrid access . . . . . . . . . . . . . . . . . . . . . . 7
5.4. Delay Tolerant Network architecture . . . . . . . . . . . 8
5.5. Dealing with varying capacity . . . . . . . . . . . . . . 8
6. Discussion on the deployability . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
10. Security Considerations . . . . . . . . . . . . . . . . . . . 9
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
11.1. Normative References . . . . . . . . . . . . . . . . . . 9
11.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
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 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]. This architecture 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
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extends the opportunities identified in this draft since they may be
also relevant for cellular networks.
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
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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
[I-D.irtf-nwcrg-network-coding-taxonomy] 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.
+------+-------+---------+---------------+-------+
| | 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. Opportunities for more network coding in satellite systems
This section extends Section 3 by presenting potential opportunities
for the deployment of network coding schemes inside satellite
systems.
These opportunities are further detailed in Section 5 and listed in
this section:
1. Two ways relay channel mode (more details in Section 5.1);
2. Reliable multi-cast (more details in Section 5.2);
3. Hybrid access (more details in Section 5.3);
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4. Delay Tolerant Network architecture (more details in
Section 5.4);
5. Dealing with varying capacity (more details in Section 5.5);
It is worth noting that these opportunities 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.
5. 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).
5.1. 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.
+------------+ +-----+ +---------+
| 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
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5.2. 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.
+------------+ +-----+ +---------+
| 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
5.3. 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. The 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.
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+-------------+ +----------------+
|->| SAT NETWORK |---| BACKBONE |
| +-------------+ | +------------+ |
+------+ | | |CONCENTRATOR| |
| CPE |-->-| +-----+ | +------------+ |
+------+ |->| DSL |-----------| |
| +-----+ | |
| | |
| +-----+ | |
|->| LTE |-----------| |
+-----+ +----------------+
Figure 5: Network architecture for an hybrid access using NC
5.4. Delay Tolerant Network architecture
** EL: ** TBD with bundle layer as a candidate for NC
5.5. 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. 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 relevant for, e.g. 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|
+------------+ +-----+ +---------+ +--------+ +---------+
Figure 6: Network architecture for dealing with varying link
characteristics with NC
6. Discussion on the deployability
This section discusses the deployability of the opportunities that
are provided 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 5.
In particular the discussion on how network coding can be integrated
inside a PEP with QoS scheduler has been proposed in RFC 5865
[RFC5865].
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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].
7. Acknowledgements
8. Contributors
Many thanks to
9. IANA Considerations
This memo includes no request to IANA.
10. Security Considerations
This document, by itself, presents no new privacy nor security
issues.
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>.
[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>.
[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>.
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11.2. Informative References
[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.
[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.
[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
Nicolas Kuhn (editor)
CNES
18 Avenue Edouard Belin
Toulouse 31400
France
Email: nicolas.kuhn@cnes.fr
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Emmanuel Lochin (editor)
ISAE-SUPAERO
10 Avenue Edouard Belin
Toulouse 31400
France
Email: emmanuel.lochin@isae-supaero.fr
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