integrating satcom and 5g: challenges and solutions

SaT5G (761413) Research Pillar White Paper February 2020

SaT5G whitepaper

Integrating Satcom and 5G: challenges and solutions

Topic ICT-07-2017

Project Title Satellite and Terrestrial Network for 5G

Project Number 761413

Project Acronym SaT5G

Actual Delivery Date 05-02-2020

Contributing WP WP4

Project Start Date 1 June 2017

Project Duration 33 months

Dissemination Level PU

Editor THALES ALENIA SPACE

SaT5G Consortium


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TABLE OF CONTENTS

Introduction ................................................................................................................................................... 3

Research Pillar I: Implementing 5G SDN and NFV in Satellite Networks ...................................................... 4

Overview .................................................................................................................................................... 4

Integrated 5G/Satellite Network Architecture .......................................................................................... 4

Adoption of 5G Network Architecture in Satellite Networks .................................................................... 6

Virtualization of Satellite Network Functions ............................................................................................ 7

SDN in Satellite Networks .......................................................................................................................... 9

Example of an SDN and NFV-enabled hybrid Satellite-5G Network.......................................................... 9

Conclusions .............................................................................................................................................. 10

Research Pillar II: Integrated Network Management and Orchestration ................................................... 10

Overview .................................................................................................................................................. 10

Analysis and development....................................................................................................................... 11

Conclusions .............................................................................................................................................. 12

Research Pillar III: Multi-link and Heterogeneous Transport ...................................................................... 12

Overview .................................................................................................................................................. 12

Multipath TCP (MPTCP) ........................................................................................................................... 13

MPQUIC ................................................................................................................................................... 14

3GPP AT3S ............................................................................................................................................... 15

5G UE using an AT3S or MPTCP function ................................................................................................ 16

UE not using an AT3S or MPTCP function ............................................................................................... 17

Regular hosts connected to the hybrid backhaul gateway ..................................................................... 17

Conclusions .............................................................................................................................................. 18

Research Pillar IV: Harmonisation of satcom with 5G Control and User Planes ......................................... 18

Overview .................................................................................................................................................. 18

Analysis .................................................................................................................................................... 19

Conclusions .............................................................................................................................................. 20

Research Pillar V: Extending 5G Security to Satellites ................................................................................. 20

Overview .................................................................................................................................................. 20

Analysis .................................................................................................................................................... 20

Satellite networks as transport network ................................................................................................. 21

Satellite network as roaming partners and as integrated access networks ............................................ 22

Conclusion and future work .................................................................................................................... 23


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Research Pillar VI: Caching & Multicast for Optimized Content & VNF distribution ................................... 23

Overview .................................................................................................................................................. 23

Caching popular content ......................................................................................................................... 24

Streaming video ....................................................................................................................................... 24

Caching content on mobile platforms ..................................................................................................... 25

Summary ...................................................................................................................................................... 25

Bibliography ..................................................................................................................................................... 27

IntroductionIntroductionIntroductionIntroduction

Mobile communication is now an essential part of our society. The pervasiveness and ubiquity of connected

services and mobile devices is at its highest point, and continuously increasing. It is expected that the

number of connected mobile devices to fifth-generation (5G) networks exceeds to 11 billion by 2021 [1] . A

huge transformation will arrive in the near future as networks continue to evolve in order to meet the

global connectivity demands such as significant increase in efficiency, expanded connectivity, instantaneous

meeting of user expectations and scalability with a larger number of devices and services. Convergence and

interoperability of different telecommunication technologies is a crucial prerequisite [2] to meet the next

generation communication goals. This technological convergence happens at all networking levels through

diverse technologies, and for significant market areas, satellite is an attractive or the only option for

providing connectivity, e.g. 5G mobile operators should deliver highly dynamic services that leverage

satellite technologies such as High Throughput Satellites (HTS).

In previous generations, the integration of satellite communication (SatCom), including mobile network

level was based on proprietary and custom solutions. Telecommunication satellites were considered

completely independent of terrestrial networks. Hybrid solutions were uncommon, and the satellite

network was mainly used to provide backhaul to a few remote and hard to access individual cells, being a

non-flexible and expensive transport network. This prevented mobile operators from effectively leveraging

satellite in mobile networks, creating challenges to service agility and programmability. Due to the wide-

scale growth of 5G networks, it is crucial to foster the development of an attractive plug-and-play SatCom

solution for 5G. This will enable terrestrial operators and network vendors to accelerate 5G deployment,

and creates new and growing market opportunities for the SatCom industry. Thus, significant efforts are

required to:

1. Design SatCom solutions, targeting integrated satellite / terrestrial 5G architectures adopting and

integrating 5G key features,

2. Exploit SatCom capabilities (e.g. broadcast, ubiquity and reliability) while mitigating its inherent

constraints (e.g. propagation latency) in standalone or multi-link network topology,

3. Ensure seamless integration of SatCom in 5G at orchestration levels,

4. Foster satellite inclusion in the 5G ecosystem as a key access network technology, to fulfill 5G

implementation in our society (by playing an active role in 3GPP and ETSI standardization efforts).

The EC H2020 project SaT5G [3] addresses the six following research pillars, to help achieving these

objectives:

1. Implementing 5G SDN and NFV in Satellite Networks,

2. Integrated Network Management and Orchestration,

3. Multi-link and Heterogeneous Transport,


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4. Harmonisation of SatCom with 5G Control and User Planes,

5. Extending 5G Security to Satellites,

6. Caching & Multicast for Optimized Content & VNF distribution.

Research Pillar I: Implementing 5G SDN and NFV in Satellite NetworksResearch Pillar I: Implementing 5G SDN and NFV in Satellite NetworksResearch Pillar I: Implementing 5G SDN and NFV in Satellite NetworksResearch Pillar I: Implementing 5G SDN and NFV in Satellite Networks

Overview

Software Defined Networking (SDN) and Network Functions Virtualization (NFV) are core technologies

within 5G. Given the comprehensive range and diversity of envisioned 5G usage scenarios, including

enhanced Mobile Broadband (eMBB), Ultra Reliable Low Latency Communications (URLLC) and massive

Machine Type Communications (mMTC), a shared physical 5G infrastructure must support a vast array of

distinct usage requirements. The 5G standard makes provision for this via the concept of network slicing, in

which isolated logical network architectures are decoupled from the underlying physical infrastructure, and

arranged in specific configurations that fulfill individual usage requirements. Central to network slicing are

the dual concepts of NFV and SDN. In order to support network slicing, 5G network components are

virtualized and equipped with SDN capabilities that enable them to be remotely deployed and modified.

Note that these virtualized network components are implemented as software, as opposed to on dedicated

hardware devices. Subsequently, those network functions may be dispatched, and arranged in a logical

configuration that implements a specific network service (i.e. slice), using SDN elements such as Controllers

and/or Orchestrators.

It stands to reason that in order to integrate satellite meaningfully with 5G, satellite network functions’

capabilities must be extended to support virtualization and SDN. While SDN and NFV are widely used in

terrestrial networks, their presence in satellite networks has been limited. In order to address this shortfall,

the SaT5G project’s Research Pillar I focuses on the research and implementation of SDN and NFV in

satellite networks.

Integrated 5G/Satellite Network Architecture

3GPP has recognized that, in order to fulfill 5G’s ambitions, a combination of both 3GPP and non-3GPP

access technologies must be considered. Consequently, 5G is the first fully access-agnostic 3GPP network

architecture. 5G supports access from multiple network types, including LTE, Wi-Fi, and crucially, satellite.

This means that, unlike previous 3GPP architectures, 5G networks are much more amenable to integration

with satellite networks. Before examining SDN and NFV for satellite networks in depth, it is first important

to understand the network architecture of an integrated 5G/satellite network. The SaT5G project

deliverable D3.1, Integrated SaT5G General Network Architecture, (see also [2]), presents a number of

reference architectures that define satellite’s position in a hybrid 5G/satellite network. Two primary

categories of network access are defined therein, as illustrated in Figure 1: Satellite positioning within 5G

network:

• Direct access: satellite-capable User Equipment (UE) has direct access to the 5G network through a

satellite link.

• Indirect access or backhaul: UE accesses a terrestrial (Radio) Access Network ((R)AN) via 3GPP or non-

3GPP access technologies. The terrestrial (R)AN is connected to the 5G core through a satellite link.


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Figure 1: Satellite positioning within 5G network

In SaT5G, both reference architectures are implemented, albeit at different levels, within the overall

network architecture. It is important at this stage to differentiate these architectural levels.

• A variant of the indirect access (backhaul) architecture defines the end-to-end (E2E) network

architecture used by 5G applications. This architecture is identified both in the SaT5G deliverable D3.1,

in [2], and in the ETSI document [4], as depicted in Figure 2: “Scenario A3 - Indirect mixed 3GPP NTN

access with bent-pipe payload”, excerpt from [4]. In this architecture, UEs connect to the 5G core

network using satellite simply as a backhaul transport network. The E2E network comprises both the

terrestrial 5G network (Mobile Network Operator (MNO) network) and the satellite network. The

terrestrial elements of the E2E network are observed in Figure 2: “Scenario A3 - Indirect mixed 3GPP

NTN access with bent-pipe payload”, colored in blue.

• A variant of the direct access architecture informs the architecture of the satellite network itself (also

referred to as the Non-Terrestrial Network (NTN)). The direct access architecture plays an important

role for next generation satellite deployments; in this architecture, the satellite network is transformed

to behave like a standard 3GPP network. This opens satellite up to the comprehensive 3GPP ecosystem,

and enables support for 5G services, such as authentication, billing, and policy & charging. The satellite

network components are shown in Figure 2: “Scenario A3 - Indirect mixed 3GPP NTN access with bent-

pipe payload”, colored in light gray.

Figure 2: “Scenario A3 - Indirect mixed 3GPP NTN access with bent-pipe payload”


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This section, Research Pillar I: Implementing SDN and NFV in Satellite Networks, focuses primarily on the

satellite network architecture, and as such, the direct access architecture is the focus of the remainder of

this section.

Adoption of 5G Network Architecture in Satellite Networks

Promotion of satellite usage in 5G systems is a primary SaT5G objective. Satellite networks have

traditionally been viewed as black-box transport pipes from the perspective of MNOs, and the integration

of both networks has been hampered by their heterogeneity. One potential way to improve

interoperability is to endow satellite networks with the capacity to present standard terrestrial network

interfaces for control and user planes, which would allow MNOs to communicate directly with satellite

components using standard 3GPP interfaces. Such integration could contribute dramatically to the uptake

of satellite in 5G.

To understand how 3GPP architecture can be used in a satellite network, it is first important to understand

the relevant concepts within a standard 5G network architecture [5]. In a terrestrial 5G network, the User

Equipment (UE) connects to the core network using the Non Access Stratum (NAS) protocol, via a 5G radio

element known as a next generation NodeB (gNB). The gNB provides 5G New Radio (NR) user and control

plane terminations to the UE, and connects to the core network’s Access and Mobility Function (AMF) [5],

[6], Session Management Function (SMF) [5], [7] and User Plane Function (UPF) [5], [8]. The UE identifies

and authenticates itself to the core network, via the N2 interface from the gNB to the AMF. Following the

establishment of sessions and default bearers, the UE can subsequently transmit user traffic through the

core network, via the N3 interface from the gNB to the UPF. A summary of these interactions is presented

in Figure 3: High-level summary of 5G end-to-end control and data paths.

Figure 3: High-level summary of 5G end-to-end control and data paths

In order to integrate a 3GPP 5G core network with a satellite network, it follows that the latter must

support, at a minimum, the NAS protocol at the NTN terminal and the N2, and N3 interfaces at the satellite

teleport. To achieve this in a real satellite network for SaT5G, a standard, virtualized, Commercial Off-The-

Shelf (COTS) 5G core network was deployed at the Avanti teleport in Goonhilly. The Avanti teleport

provides the satellite gateway for the SaT5G 5GIC test bed. Subsequently, relevant satellite functions were

modified such that they presented themselves as standard 5G network components to that core.

Specifically, the concept of an non-terrestrial network (NTN) UE was introduced. This new, 3GPP-enabled

satellite terminal implements the NAS protocol towards the core network’s Access and Mobility

Management Function (AMF), and Session Management Function (SMF), thus enabling it to present itself as

a 5G UE to the SatCore. This allowed the satellite terminal to connect to an NTN 5G core network in order

to access network services. Correspondingly, the satellite RAN (SatRAN) was augmented to support the 5G

N2 and N3 interfaces. The SatRAN subsequently presents to both the NTN terminal and the SatCore as a

gNB. This SatRAN gNB interfaces with the NTN 5G core network on the network side, while continuing to


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use the existing satellite radio over the satellite link (as the 5G NR is not currently implemented over

satellite).

It is important to note that modifications were made solely to satellite elements, and that no modifications

were required to the standard 5G core network, which now operates and controls the satellite network.

Importantly, the physical layer remains the same over the satellite for the NTN network. The resultant

network architecture is presented in Figure 4: Modification of satellite network elements in 5GIC test bed to

support 5G core network integration.

Figure 4: Modification of satellite network elements in 5GIC test bed to support 5G core network integration

Virtualization of Satellite Network Functions

Fundamentally, satellite communications exhibit the same characteristics as other wireless technologies

and can therefore adopt the NFV paradigm to a similar degree. A subset of physical satellite functions, (e.g.

satellite hub chassis, RF line cards, satellite terminal) usually run on dedicated hardware, in contemporary

deployments, while some lower layer functions in the satellite radio domain are best suited to run as

physical network functions, on account of their static high throughput compute functionality – this also

applies to terrestrial wireless networks also. However, the upper satellite radio and network layers are all

suitable for virtualization, analogous to layers 2 and 3 of the 3GPP RAN architecture. Virtualization of the

upper satellite radio and network layers was achieved in SaT5G by adhering to the industry-standard ETSI

NFV-MANO framework [9].

The ETSI NFV-MANO framework, produced by the ETSI ISG ETSI-NFV [9], defines standardized domains,

elements, and reference interfaces that comprise an SDN and NFV-capable system. A diagrammatic

representation of the framework, excerpt from [9], is reproduced here for reference in Figure 5: ETSI NFV-

MANO reference architectural framework.


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Figure 5: ETSI NFV-MANO reference architectural framework

Most relevant to the ensuing discussion are the VNF, NFVI, Virtualization Layer, Orchestrator, Virtual

Infrastructure Manager, and Service, VNF and Infrastructure Description elements. Following the approach

prescribed by the NFV-MANO architecture, these elements were introduced to a satellite network at

various architectural layers to achieve NFV and SDN functionality. A brief overview of these elements

follows:

• VNF: Virtual Network Function, a software implementation of a network function.

• NFVI: Network Function Virtualization Infrastructure, (physical) infrastructure that provides the

resources that are abstracted by the virtualization layer and used by VNFs.

• Virtualization Layer: provides abstraction of physical resources for VNFs, coordinates and arbitrates

allocation of physical resources to VNFs. Also known as a hypervisor.

• Orchestrator: software agent that coordinates virtual and physical resources for the provision of

network services. Provides a northbound API for interaction with business and operation-level systems,

and southbound APIs for communication with VNF manager(s) and/or VIM(s). In the case of the 5GIC

test-bed, the Orchestrator works directly with the VIM to arrange underlying resources for provision of

a satellite network service.

• Virtual Infrastructure Manager: manages Network Function Virtualization Infrastructure (NFVI), which

may be physical and/or virtual. Exposes a northbound API for interaction with the Orchestrator, and a

southbound API towards the underlying NFVI. VIM responsibilities include allocation and modification

of VM resources, and provision of VM network connectivity.

• Service, VNF and Infrastructure Description: text-based descriptor files consumed by the Orchestrator.

Typically written in YANG [10] modeling language and encoded in JSON or XML, descriptors define VNF-

specific resource requirements and the inter-VNF virtual forwarding graphs that define a network

service.

Unsurprisingly, the NFV-MANO Virtualization Layer is the primary mechanism by which satellite network

function virtualization is achieved. In practice, this necessitates the introduction of a hypervisor (such as

KVM) to the satellite teleport, which abstracts the underlying physical host system’s resources (i.e. the

NFVI) such that they may be shared among numerous virtual functions. For SaT5G, four reference satellite

network functions that traditionally required dedicated hardware resources, were virtualized. These

functions are: Satellite Radio Access Network (SatRAN), Satellite Core Network (SatCore), Layer 2 over

Satellite Function (L2oS), and Satellite Gateway Function (Sat G/W). The respective purposes of the SatRAN


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and 5G core VNFS have already been discussed. The L2oS function, then, provides the Layer 2 over Satellite

service, while the Sat G/W Function forwards traffic between the satellite and terrestrial data networks. All

satellite VNFs were collocated and deployed on a single COTS general-purpose server, thus achieving a

reduced hardware footprint by increasing compute density. The result is illustrated in Figure 6: Colocation

of multiple satellite VNFs on COTS hardware.

Figure 6: Colocation of multiple satellite VNFs on COTS hardware

SDN in Satellite Networks

Each satellite network function implements a dedicated purpose, which typically only represents a single

element within an overall larger network service. In other words, a network service is comprised of multiple

VNFs, which are arranged in a specific configuration to implement that service. Deploying a network service

by manually instantiating and configuring each VNF element of a network service using a VIM is inefficient

and error-prone. Instead, SDN network services are typically deployed automatically by SDN orchestrators.

To that end, VIMs expose northbound APIs that support integration with SDN orchestrators.

In order to deploy network services, the SDN orchestrator needs to understand those network functions

that comprise a service, the resources that those functions require, and the network topology of the

network service. This refers to the Service, VNF and Infrastructure Description in the ETSI NFV-MANO

architecture. In the case of SaT5G, satellite services were deployed using the Open Source MANO (OSM)

orchestrator, using YANG (Yet Another Next Generation) [10] descriptors, which are text-based files,

typically encoded in JSON or XML. By developing ETSI-standardized YANG descriptors, which capture

network functions’ resource requirements and the required network topology, satellite VNFs were on-

boarded to OSM and subsequently deployed as a satellite service.

Example of an SDN and NFV-enabled hybrid Satellite-5G Network

The Figure 7: Example of an integrated satellite/5G network in SaT5G illustrates a real-world

implementation of a hybrid satellite / 5G network, replete with SDN-capable satellite VNFs, and automated

deployment of satellite network services via Open Source MANO (OSM). The presented network

architecture, realized in the SaT5G project’s 5G Innovation Centre (5GIC) test-bed implements all of the

topics discussed in this section:


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• The green and yellow nodes represent the remote and central nodes of a terrestrial 5G network,

respectively. These nodes implement the indirect access architecture, whereby each side of the

terrestrial 5G network is bridged by a satellite backhaul

• The satellite network implements the direct access architecture, in which the NTN terminal acts as a

satellite-capable 5G UE, which access the 5G NTN core directly over satellite

• The teleport houses satellite VNFs, which are deployed using the OpenStack VIM on a single COTS

server

• The 5GIC central node deploys a subset of the satellite network service using the OSM Orchestrator,

using OSM descriptors and satellite VNF images

Figure 7: Example of an integrated satellite/5G network in SaT5G

Conclusions

We have demonstrated thereby that the virtualization of satellite resources is both viable, and can be

augmented to support SDN and orchestration for improved integration within 5G networks. We also

conclude that adoption of 3GPP network architecture in satellite networks presents extensive benefits,

such as feature parity with terrestrial networks (for example, network roaming), simplified integration with

terrestrial networks via implementation of standard terrestrial network interfaces, and reduced time to

market via integration of third-party components (for example, terrestrial billing systems).

Research Pillar II: Integrated Network Management and OrchestrationResearch Pillar II: Integrated Network Management and OrchestrationResearch Pillar II: Integrated Network Management and OrchestrationResearch Pillar II: Integrated Network Management and Orchestration

Overview

In order to consider the seamless integrating satcom into the 5G management and orchestration (MANO)

the SaT5G took as its basis the TALENT MANO system [11].

TALENT is a coordination solution, produced by one of the SaT5G partners, which supports end-to-end

services composed of satellite, radio access, cloud and mobile edge computing resources. TALENT features

these important aspects:

• TALENT is not vendor-locked and can support satellite and radio elements of different vendors.

• TALENT is NFVO (e.g. OSM, ONAP) and VIM (e.g. OpenStack) agnostic.

• TALENT covers end-to-end service management over cloud and edge computational resources.


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• TALENT provides a single and easy to use point of interaction for all stakeholders involved in the

ecosystem, e.g. terrestrial and satellite operators as well as different 5G end user verticals.

Analysis and development

Having these objectives in mind and based on the frameworks suggested by ETSI MANO [12] and 3GPP SA5

[13], this work proposes an extension towards satellite integration at the management and orchestration

level. Figure 8 illustrates the proposal. The NFV-MANO stack, i.e. Network Function Virtualized Orchestrator

(NFVO), Virtual Network Function Manager (VNFM), Virtual Infrastructure Manager (VIM) and cloud Virtual

Network Functions (VNFs), represents the ETSI MANO framework [14]. The ETSI MANO framework targets

the lifecycle management and configuration of cloud services over the Network Function Virtualization

Infrastructure (NFVI). In [15] , the original ETSI MANO framework was reviewed to introduce radio

resources. Those resources are presented by Radio VNFs, Radio Physical Network Functions (PNFs) and

Domain Manager (DM). Radio Element Managers (EMs) embedded on the DM are included on the 3GPP

framework to configure the Radio PNFs, thus supporting end-to-end service lifecycle management (service

instantiation, termination, scaling, etc.) in a mixed radio cloud environment. With the same methodology,

this work proposes to extend the 3GPP framework by including satellite elements, i.e. satellite VNFs (e.g.

propagation impairments mitigation VNF for the satellite ground gateway), satellite PNFs and satellite DM

including satellite EMs.

The proposed framework clearly represents three identical domains (cloud/edge, radio and satellite)

interworking with each other to deliver end-to-end services. The idea of having satellite connectivity along

with radio and cloud/edge capacity is not new. However, in the traditional way, the actual process of

launching and managing such a complex service demands a significant amount of manual operations and

processes.

Figure 8 Proposed integrated Terrestrial and Satellite framework.

Such a manual process hinders the end-to-end service provisioning and lifecycle management, increases

risk of human errors and reduces the satellite terrestrial services business desirability. Adapting TALENT is a

solution developed within SaT5G to tackle this problem. It provides an over-the-top management layer

with a holistic view over all available services and resources. TALENT helps building a multi-tier

orchestration stack over a heterogeneous environment, featuring a single point of interaction for all

stakeholders engaged in the ecosystem (satellite, terrestrial and cloud operators as well as 5G vertical

sectors) enabling them to automatically launch and manage end-to-end satellite terrestrial services. It is

completely in line with the 5G high level KPIs such as reducing service provisioning from 90 hours to 90

minutes [16].


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Conclusions

These adaptations of TALENT were validated and demonstrated as part of the SaT5G Zodiac Inflight

Innovation (Zodiac Aerospace group) test-bed to provision and configure the required end-to-end service

(composed of cloud/edge and satellite), as well as to efficiently deliver refreshable and live contents on

board from the ground into the airplane. The workflow is as follows:

• On the bootstrapping phase, TALENT is loaded with proper information about the domains under

control. In the first release, it supports OSM release 4, 5 and 6 for the cloud and TotalNMS of Gilat for

the satellite. In addition, TALENT get to know about 5G application, which will be provisioned, i.e.

Broadpeak video multicast solution.

• In the operation phase, first TALENT sets up service in the cloud environment with proper VNFs and

internal virtual networks to reach the provisioned NS between Munich and satellite gateway location.

After receiving the acknowledgment from the cloud side, TALENT sends the configuration file to the

ground station of satellite system. With this configuration file, TALENT completes the provisioning of

satellite connectivity from the ground to the airplane cabin mock-up. Once the connectivity is in place,

and it has been acknowledged, TALENT inform 5G application to launch video multicasting.

More details of TALENT, including high-level design and internal architecture is presented in [11].

Research Pillar III: MultiResearch Pillar III: MultiResearch Pillar III: MultiResearch Pillar III: Multi----link and Heterogeneous Transportlink and Heterogeneous Transportlink and Heterogeneous Transportlink and Heterogeneous Transport

Overview

SaT5G aims at delivering the seamless integration of satellite into 5G networks and thereby ensure

ubiquitous 5G access. Nowadays UEs are equipped with multiple access technologies including, Wi-Fi, 3G,

4G, and even 5G to connect to the internet anywhere and anytime. This is especially true with the satellite

communication, which offers connectivity in hostile and isolated environments. Employing several paths

simultaneously has emerged as an efficient way to: (i) improve the throughput by aggregating bandwidths

of multiple paths, (ii) increase the fault tolerance by duplicating the traffic over multiple paths, (iii) prevent

congestion as the traffic is balanced across the chosen paths, and finally (iv) reduce the delay.

Satellite high latency being a major challenge for 5G’s reactivity requirements, SaT5G analyses possible link

aggregation protocols evolution and adaptability to satellite links at backhaul level in a 3GPP multi-access

AT3S standards context – cf. Figure 9. Recent multi-link protocols such as MPTCP and MPQUIC, including EC

FP7 BATS’ [17] multi-link (satellite / terrestrial) transport protocols are combined to setup an hybrid

backhauling. A new BT3S (Backhauled Traffic Steering, Switching and Splitting) function is proposed as an

extension of 3GPP AT3S (Access Traffic Steering, Switching and Splitting) [18], [5], [19] for the backhaul –

leading to a contribution from SaT5G to 3GPP.


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Figure 9 Backhaul implementation options identified by SaT5G

Multipath TCP (MPTCP)

MPTCP is a fully compatible extension of the TCP protocol, published as an experimental standard in 2011

[20] [21] and currently widely deployed [22]. MPTCP scheduling, i.e. sending data on the available paths,

follows the Lowest-RTT-First (Low RTT) policy [23], Weighted Round Robin scheduler [24], [25], the Earliest

Completion First (ECF) algorithm [26], or Slide Together Multipath Scheduler (STMS) [27]. The FP7 BATS

project added Packet Steering Based on Object Length (PSBOL) scheduling where short objects are sent

over the lowest latency link while long objects are sent over the highest bandwidth link. Combining PSBOL

and Offload as Path Selection algorithms was demonstrated in the H2020 VITAL project. Technical report

103 272 [28] published by ETSI in 2015 focuses on proposing an hybrid access network combining one or

several terrestrial access technologies (Fixed or Mobile Service) together with a satellite broadband access

network (Fixed Satellite Service).


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Figure 10 Hybrid access using multiple paths between gateways - ETSI

ETSI’s hybrid architecture shown in Figure 10 involves a customer’s premises gateway and a network

gateway, with multiple networks between them. The multiple networks are hidden from the hosts, so it

looks like a normal network but with better performance.

MPQUIC

A protocol named QUIC (Quick UDP Internet Connections) has been designed in recent years to address TCP

handshake delay and the Head-of-line blocking issues. QUIC introduced by Google in 2013 is considered for

standardization by the IETF [29] [30]. QUIC incorporates the TLS 1.3 key negotiation requiring the entire

connection to be encrypted, and is carried over UDP transport protocol. QUIC aims to be equivalent to TCP

with better performance. Figure 11 depicts a comparison between the TCP and QUIC protocol stacks

combined with HTTP/2.

Figure 11 Comparison of TCP and QUIC protocol stacks

The multipath version of QUIC takes the same basic approach as MPTCP. An early comparison of MPTCP

and MPQUIC, using measurements on an emulation platform, shows MPQUIC outperforms MPTCP with a

better loss signaling, more precise latency estimation, and improved fairness in the evolution of the

congestion window of paths. However, QUIC’s end-to-end encryption prevents an implicit MPQUIC proxy.


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3GPP AT3S

From a 3GPP perspective, one of 5G objectives is to provide new radio and new 3GPP access technologies.

Therefore, it is possible to use existing access technologies to provide increased throughput, robustness and

mobility). In that light, the 3GPP consortium have described [18], [5], [19]how to enable multi-access to

both 3GPP and non-3GPP technologies. The SA2 3GPP working group is studying 5G multi-link aspects. The

documents [18], [5], [19] describe how the 5G System (5G UE and CN) can be extended to support Access

Traffic Steering, Switching and Splitting (AT3S) between 3GPP and non-3GPP access networks:

•••• Access Traffic Steering: procedure selects an access network for a new data flow and transfers the

traffic of this data flow over the selected access network. Access traffic steering is applicable between

3GPP and non-3GPP accesses,

•••• Access Traffic Switching: procedure moves all traffic of an ongoing data flow from one access network

to another access network in a way that maintains the continuity of the data flow and service. Access

traffic switching is applicable between 3GPP and non-3GPP accesses,

•••• Access Traffic Splitting: procedure splits the traffic of a data flow across multiple access networks.

When traffic splitting is applied to a data flow, some traffic of the data flow is transferred via one

access and some other traffic of the same data flow is transferred via another access. Access traffic

splitting is applicable between 3GPP and non-3GPP accesses.

Note that 3GPP is focusing on access technologies, and not on the backhaul. In the scope of SaT5G, where

satellites are used for the backhaul, the main focus is on understanding the 3GPP mechanisms used for the

AT3S to move towards mapping these mechanisms with the SaT5G architecture, including backhaul. In 5G

and in 4G, UE needs to set up a (data) connection in order to connect to Data Network (DN). In 5G

terminology, PDU session setting up is detailed in 3GPP TS23.502 [31]. Hybrid backhaul requires Multi-

Access PDU (MA PDU) session where multiple PDU sessions (at least two) are running in parallel, and

considered by the rest of the system as a single MA PDU session – cf. Figure 12 excerpt from 3GPP TR

23.793 [18].

Figure 12 MA PDU session

In cases where the RAN nodes are connected via multiple types of backhaul connections, including

DSL/cellular networks and satellite connections, there is a need to have mechanism to handle Backhaul

Traffic Steering, Switching, and Splitting (BT3S). In such hybrid backhaul architecture Figure 13, non 5G

hosts connected to the gateway benefit also from the availability of Steering, Switching, and Splitting

functions over the multiple available links. AT3S focuses on access while BT3S addresses the backhaul links

between gNB and Core Network. The backhaul could combine 3GPP (5G) and non-3GPP links.


SaT5G whitepaper

UEgNB

gNB-BT3SF

N3IWF

AMF

AUSF

UPF

UPc-BT3SF

Upu-BT3SF

Data

network

SMF

CP-BT3SF

PCF

PC-BT3SF

UDM

UDR-BT3SF

AF

Figure 13 Multi-link in backhaul using BT3S

The above technologies, when combined, support the following three use cases:

• 5G UE using an AT3S or MPTCP function,

• 5G UE not using an AT3S or MPTCP function,

• Regular hosts connected to the hybrid backhaul gateway.

5G UE using an AT3S or MPTCP function

When the 5G UE supports AT3S or MPTCP, a solution is to extend the AT3S in order to have in the AT3S UE

the possibility to establish several MA PDU child sessions over the 5G interface; e.g. one child PDU session

for the satellite backhaul link, one for the terrestrial backhauling link, and to DSCP mark the packets

accordingly – cf. Figure 14. Then the hybrid backhauling gateway performs policy based routing to transmit

the corresponding packets on the appropriate links. Another flag may be used if DSCP is modified by the

satellite system.

Figure 14 BT3S with AT3SF UE


SaT5G whitepaper

UE not using an AT3S or MPTCP function

When the UE does not support AT3S or MPTCP, a solution is to implement in the hybrid backhauling

gateway, an MPTCP proxy that intercepts the TCP flows inside the GTP-U traffic and use MPTCP to transport

the traffic over the available links – cf. Figure 15. The GTP domain is shown at the top of the figure.

At the central site, an MPTCP proxy ends the MPTCP sub-flows and deliver the original TCP traffic.

Figure 15 BT3S with non AT3SF UE

Regular hosts connected to the hybrid backhaul gateway

Non 5G hosts must be considered. Provided that the hybrid backhauling gateway acts as an hybrid UE with a

satellite and a terrestrial interfaces, a possible solution is to use the regular 5G AT3S function to transport

the traffic of these hosts on the available links – cf. Figure 16.

Figure 16 BT3S with regular (non 5G) hosts


SaT5G whitepaper

Conclusions

The Sat5G project allowed to experiment those architectures with an hybrid backhauling network with a

low bandwidth and low latency terrestrial link combined with a high bandwidth and high latency satellite

link. It demonstrated the performances are significantly improved if a multipath protocol such as MPQUIC

with a good Path Selection Algorithm are used. Current multipath protocols use Path selections algorithms

such as Round Robin or Offload that provide bandwidth aggregation. That is fine for download exchanges

but under-optimal for interactive operations because some packets are sent on the unwanted high latency

link. Path Selection Based On Object Length where short objects are sent on the low latency link and long

objects on the two links using Round Robin or Offload solves the issue for interactive exchanges while

leveraging the bandwidth aggregation capacity. The experimentation based on MPQUIC with PSBOL+ WRR

path selection outperforms the use of a Satellite or ADSL link by itself or the use of the two links with

MPQUIC + RR for all types of applications, including HTTP2 Web browsing: SaT5G multi-link prototypes

demonstrate that the concept of multi-link backhauling is possible with the multi-link protocol done in the

client and the server and the multi-link interfaces placed on remote equipment of the backhauling network.

There are three directions that should be further investigated:

• AT3S extensions to support the use in splitting protocols of several sub-flows on the 5G interface and

the use of Path Selection algorithms based on the size of the exchanged objects,

• In each multilink protocol (MPTCP, MPQUIC), how to avoid retransmissions of packets belonging to

short objects on high delay links,

• Use the BT3S concept in order to fully integrate satellite links in 5G networks.

Research Pillar IV: HResearch Pillar IV: HResearch Pillar IV: HResearch Pillar IV: Harmonisation of satcom with 5G Control and User Planesarmonisation of satcom with 5G Control and User Planesarmonisation of satcom with 5G Control and User Planesarmonisation of satcom with 5G Control and User Planes

Overview

One form of integration is to apply 5G NR into satellite systems. However, 5G NR was designed for

terrestrial systems and therefore all SATCOM (satellite communications) constraints have not been taken

into account. At the physical (PHY) and medium access (MAC) layers the large Doppler frequency shift and

large propagation latencies met in satellite systems form the basis of misalignment.

LEO satellites move at 7 200 m/s (or nearly 26 000 km/h) that results 720 kHz Doppler frequency shift at 30

GHz carrier and 8.2 kHz/s Doppler change rate. This exceeds the 5G NR design speed 500 km/h by a huge

margin. The satellites are at 600 km or higher whereas maximum design terrestrial cell size is 300 km at 15

kHz subcarrier spacing (SCS) that distance scales down with increased SCS. In addition, the satellite

footprint (beam size at Earth’s surface) can be larger than 1 000 km (in one or both dimensions).

This means that satellite receivers must be able to handle large carrier frequency offsets (CFOs) whose

value exceeds that of the SCS. In the terrestrial systems this is not the case and simple receivers can be

used. The needed receiver structure is known from the GNSS systems that have a similar problem. Basically,

if one want a fast acquisition (initial downlink synchronization) parallel receivers tuned to different CFO are

needed that makes the receiver signal processing more demanding [32]. After initial large CFO is solved, a

usual receiver is enough. 5G NR was designed to be very flexible and it has modes where reference symbols

are quite frequent that allows sufficient CFO tracking.


SaT5G whitepaper

Figure 17. The structure of (one shot) large CFO aware receiver.

Analysis

The 5G NR initial downlink access is designed down to -6 dB signal-to-noise ratio (SNR) per resource

element. The satellite systems link budget must satisfy this. Otherwise, the signal structure must be

redesigned, e.g., by extending the downlink synchronization signals [32]. The data part is not this sensitive

and requires more SNR, such that changes are needed for modulation and coding if satellite link budgets

are not adequate.

To maximize the SNR, the output back-off of the satellite’s high power amplifier (HPA) is kept as small as

possible. This is in contrary to a high peak-to-average-power ratio (PAPR) of 5G NR OFDM signal. It was

shown that the PAPR of the 5G NR synchronization signal can be reduced down to 1 dB level without

significant sensitivity losses such that 1.5 dB back-off can be used in the HPA. This has to be verified for the

data part though and, most probably, density of the reference symbols will play a crucial role.

A user equipment (UE) (or satellite system user in this case) is time alignment during the random access

process. Initially, the UE gets its timing from the downlink synchronization signal for its random access

signal (PRACH). This timing includes large uncertainty, up to cell edge. Luckily, in 5G NR the scheduler

handles the required guard interval, such that large satellite uncertainties can be managed by designing a

proper scheduler [33]. After receiving PRACH, the base station (BS) (at the satellite or at the satellite

ground segment) can calculate the timing advance (TA) value that is used to fine tune the UE timing.

Unfortunately, only 12 bits are reserved for TA value at the random access response (RAR) message send by

the BS to the UE. More bits are needed to cover satellite propagation latencies. However, if the satellite

system could send a minimum distance information (also known as differential delay) within the beam (that

is a time varying parameter) in system information that is read by the UE before it starts its own emissions,

the minimum distance value could be subtracted from the propagation latency that would reduce the

required TA value. However, the satellite footprint size could be over 1 000 km such that this would not

totally eliminate the need for extra bits. Footprint size, like satellite velocity, depends on a satellite system

such that flexible solutions are needed to cover all options. Furthermore, the timers related to the random

access process need to be extended properly for each satellite system, but this is just parameter setting

[34].

At the uplink direction, the BS receives signals from many UEs simultaneously. However, in satellite systems

these signals have potentially very different CFOs and require guard bands between, basically based on the

worst case scenario for that particular satellite system. The scheduler should carefully think is the OFDMA


SaT5G whitepaper

or TDMA or their hybrid principle better for particular satellite system. Luckily, 5G NR leaves scheduler

design for vendors such that satellite optimized schedulers are possible, and this is obviously a very

relevant research question. At the same time, proper transmission time intervals (TTIs) should be planned

for different satellite systems. TTI planning goes hand in hand with the design of a satellite friendly HARQ

system.

Although 5G NR is very flexible it cannot support all the requirements coming from the satellite systems

and in addition to parameter selection also some changes to the standard are needed. Furthermore, better

receiver algorithms and optimal scheduling methods for NTN friendly systems still ask for further research.

Conclusions

This research pillar led to several scientific publications [32], [34] and a major contribution to 3GPP TR

38.811 [35], which identified classes of issues for adapting NR interface.

This research pillar also characterized the potential impacts of longer delay on N1 reference point (UE -

AMF, UE - SMF interfaces), N2 reference point (NTN gNB - AMF and NTN gNB - SMF interfaces), N3

reference point (NTN gNB – UPF interface) and associated protocol layers on these interfaces, such as NAS

(Non-Access Stratum), NGAP (Next Generation Application Protocol), SCTP (Stream Control Transmission

Protocol), GTPv1-U (GPRS Transport Protocol, for the user plane), and on the NR interface, PDCP (Packet

Data Convergence Protocol), RRC (Radio Resource Control protocol) and MAC (Media Access Control).

These former results, completed by 3GPP TR 38.821 [36] are useful for any implementation, as guidelines.

Research Pillar V: Extending 5G Security to SatellitesResearch Pillar V: Extending 5G Security to SatellitesResearch Pillar V: Extending 5G Security to SatellitesResearch Pillar V: Extending 5G Security to Satellites

Overview

Security in mobile networks in general and in 5G networks in particular focusses on the following aspects:

• Authentication and authorization,

• Integrity and replay protection and

• Confidentiality protection.

Analysis

Authentication and authorization are about verifying the identity of mobile devices/users and authorizing

their access to the mobile network. In mobile networks this type of security is achieved by precisely

standardized authentication protocols that make use of secret shared long-term keys stored in specialized

chips (the so-called SIM cards, or more formally USIM – Universal Subscriber Identity Module) and in secure

databases in the network (in 5G in the so-called ARPF – Authentication Repository and Processing

Function).

Figure 18: Authentication based on secret shared keys in USIM and ARPF

Integrity protection is related to protection against tampering of messages and data and confidentiality

protection is related to protection against eavesdropping of messages and data. Traditionally in mobile

networks this type of protection is fully standardized for messages and data exchanged over-the-air by user


SaT5G whitepaper

devices (UE – User Equipment) and the radio network (RAN – Radio Access Network). Protection is also

expected for interfaces between networks (the so-called interconnection) and for internal interfaces (e.g.

for interfaces between the radio network and the core network, CN – Core Network, the so-called

backhaul), but protection of these interfaces is far less extensively standardized. For instance, for

protection of backhaul, the security mechanism of IPsec is suggested but its use is not mandatory.

In 5G networks an additional security aspect has gained more attention:

• Privacy protection.

Privacy protection is about protection against disclosure of user related information via which behavior,

location, and movement of users can be determined. In 5G networks this type of protection focusses on the

so-called subscriber identity, which in 2G/3G/4G network is called IMSI – International Mobile Subscriber

Identity, and in 5G networks is called SUPI – Subscription Permanent Identifier. The identifier is related to

the subscription of users (i.e. it is not their mobile telephone number), it is stored on the USIM, and it is

used for verifying a user's access to a mobile network. In 5G networks the SUPI is encrypted when sent

over-the-air from UE to RAN.

Security in satellite networks currently is satellite specific and mostly proprietary. The focus in this case is

on:

• Modem/terminal security, i.e. protection against unauthorized access to modems/terminals and to

connecting unauthorized modems/terminals to satellite networks.

• Transmission security, i.e. protecting the forward link (from satellite gateway to modem/terminal) and

protecting the return link (from modem/terminal to satellite gateway). Due to differences with respect

to the power and transmission techniques used for these links, different techniques for protection can

be used.

• Network/gateway security, i.e. protection against unauthorized access to gateways, management

systems, and satellites.

In integrated satellite/terrestrial 5G networks a number of security aspects have been investigated in the

SaT5G project. The security aspects studied depend on the integration scenario.

Satellite networks as transport network

In the case of satellite networks used for indirect access, i.e. used as transport network by terrestrial

networks, e.g. for backhaul, security mechanisms needed depend on:

• What is the trust relation between the terrestrial network operator (MNO – Mobile Network Operator)

and the satellite network operator (SNO – Satellite Network Operator)?

• How many terrestrial network operators are served by the same satellite network?

• How much are the management systems of the MNO and the SNO integrated?

Traditionally MNOs protect their backhaul connections (i.e. between RAN and CN) by using IPsec: all traffic

(both signaling and data) is fully encrypted over a single IPsec tunnel between RAN and CN. In this case,

network features of satellite networks, such as TCP acceleration and QoS differentiation, cannot be used by

these networks. Optimal usage of satellite networks in this scenario, therefore requires a different mode of

cooperation between MNOs and SNOs, so that different deployments of security mechanisms can be

arranged, e.g. use of other security mechanisms than IPsec, or a different way of deploying IPsec, e.g. using

TCP acceleration outside the IPsec tunnel.


SaT5G whitepaper

UE

RAN

CN

Over-the-air

ARPFUSIM

Figure 19: MNO common practice of using IPsec over backhaul connections

UE

RAN

CN

Over-the-air

ARPFUSIM

TCP Acc. TCP Acc.

Figure 20: Alternative deployment of IPsec enabling TCP acceleration over satellite links

Serving multiple MNOs by a single satellite network may require the use of techniques such as network

slicing providing isolation between slices. Instead of the 5G defined concept of network slicing also

proprietary techniques based on network virtualization may be used.

In most cases, the use of satellite networks as transport network benefits from having integration between

management systems of both MNOs and SNOs. Integration of these systems would benefit from

standardized security mechanisms such as exposure functions, but standardization of such security

mechanisms is only starting to appear currently and may not lead to fully standardized solutions. It is

therefore expected that proprietary mechanisms are needed in this area.

Satellite network as roaming partners and as integrated access networks

In the case of satellite networks with direct satellite access, i.e. satellite networks acting as roaming

partners for MNOs, or satellite networks integrated into MNO networks as another type of access network,

the security mechanisms needed are mostly related to incorporating the 5G security mechanisms into

satellite networks. That is:

• Satellite networks need to perform authentication based on USIMs and the standardized 5G

authentication mechanisms and

• Satellite networks need to perform integrity protection and confidentiality protection for the satellite

links according to the standardized 5G security mechanisms and using the standardized 5G keys.

The mechanisms for protection of the satellite link depend on the architecture used for the satellite access

network:

• In the case of satellite access networks fully implementing NR – New Radio 3GPP access, the security

mechanisms shall need to comply fully with the 3GPP defined mechanisms.

• In the case of satellite access networks implementing an untrusted or trusted non-3GPP access

network, the satellite networks need to support the corresponding security mechanisms, such as IPsec

between UE and RAN and the corresponding usage of 5G defined keys.


SaT5G whitepaper

Figure 21: Satellite networks as trusted non-3GPP access in 5G networks

In both cases the satellite network need to follow 3GPP standards to a higher agree than is customary

nowadays.

Within the SaT5G project the impact of satellite connection on existing 5G security mechanisms has been

studied with respect to the following concerns:

• How does the added delay caused by satellite connections impact the existing security procedures and

what needs to be changed?

• How do the existing security procedures affect the load on satellite connections, especially in view of

mobility of devices?

The conclusion of the above two topics has been that the concerns do need changes in the 5G networks.

On the one hand, the existing security procedures are not impacted by the expected extra delays caused by

satellite connections: delays caused by GEO – Geostationary Earth Orbit satellite is expected in the range of

300 – 600 ms, whereas timers in security procedures are in the order of 6 s. On the other hand, security

procedures protecting over-the-air connections mostly consist of a single handshake (one message, and

one message back) in combination with mostly local generation of keys. Therefore security procedures are

not expected to contribute to load much, and they can hardly be improved.

Conclusion and future work

Security in integrated satellite/terrestrial networks is important, but does not have to lead to additional

standardization in 3GPP. It does, however, benefit or even require a closer cooperation between MNOs and

SNOs. Cooperation can be on the usage/non-usage of IPsec and it can be on the integration of MNO and

SNO management systems. Deploying virtualization techniques such as network slicing can provide a good

basis for supporting multiple MNOs by the same satellite network.

Integration of satellite networks based on direct access needs satellite networks to incorporate 5G security

mechanisms such as the use of USIMs and 5G authentication procedures. The use of trusted non-3GPP

access architecture in satellite networks may be a good first phase in the road towards full

satellite/terrestrial integration.

Research Pillar VI: Caching & Multicast for Research Pillar VI: Caching & Multicast for Research Pillar VI: Caching & Multicast for Research Pillar VI: Caching & Multicast for OptimizedOptimizedOptimizedOptimized Content & VNF distributionContent & VNF distributionContent & VNF distributionContent & VNF distribution

Overview

This research pillar focuses on specific techniques developed for supporting mobile broadband content and

NFV software delivery services in satellite-backhauled 5G environments. It covers a wide variety of research

topics including offline multicast and caching of popular content at 5G mobile edge, DASH (Dynamic

Adaptive Streaming over HTTP) based video content delivery including live streaming and video on demand

application scenarios, as well as content delivery optimization to moving platforms such as airborne flights.


SaT5G whitepaper

Caching popular content

First of all, the project investigates the framework and analyses the benefits of caching popular content at

5G mobile network edges for enabling localized access by end users. The key idea is to leverage GEO

satellite resources to multicast predicted popular content during off-peak time towards targeted 5G mobile

edges. When it comes to the time point where local end users start to make their content requests, such

popular content has already been available to be consumed locally from the mobile edge. The benefits are

two-fold: first, the user quality of experiences (QoE) can be significantly improved due to the much reduced

access and transmission latency compared to the scenario where content has to be streamed from the

remote servers. In addition, the backhaul content traffic over the 5G core network can also be substantially

reduced. This solution is especially useful for reducing backhaul traffic during peak-time period when an

overwhelming number of end users may simultaneously start content consumptions.

Streaming video

The second topic under this pillar is the feasibility study on using satellite backhaul to stream 4K/4K+ video

content in real-time over the 5G core. The key challenge here is the long end-to-end latency over the

satellite link which will cause poor end-to-end performance based on today’s transport protocols. The

project team aims to achieve QoE-assured delivery of 4K/4K+ quality video content in such a challenging

environment, especially for some rural areas where deployment of terrestrial backhaul is too expensive or

even not possible. In order to tackle the adverse effect on the end-to-end data throughput performance

introduced by the satellite link latency, we developed a context-aware user plane function (UPF) at the

mobile edge which is responsible for pre-fetching, buffering and adapting MPEG DASH video segments on

the fly in order to make sure the actual video buffer on the user device side is not starving, provided that

the last-mile radio access network (RAN) has adequate resources. Such a UPF can be realized based on the

multi-access edge computing (MEC) platform embedded in the 5G network as shown in Figure 4.

Figure 22: The MEC platform for supporting 4K/4K+ DASH video streaming

This scheme has been further extended to the 5G multi-link environment. For some rural areas where the

capacity of the terrestrial backhaul is limited, the satellite link will be able to provide complementary

content transmission services in parallel. In this case, how to ensure user QoE (including fairness between

users) while making sure the network resources along the two backhaul links are optimized becomes an

essential challenge. The project team developed a set of techniques for intelligently splitting video content

segments (or segment layers) to be delivered through parallel terrestrial and satellite backhauls such that

all the on-going video sessions are treated in a fairness way in terms of user experienced quality.


SaT5G whitepaper

Caching content on mobile platforms

For the sake of extending the benefits of content caching to different scenarios, this research pillar also

investigates cost-efficient approaches to the delivery of mobile broadband content to moving platforms

such as airborne aircrafts through satellite-enabled 5G network (Figure 23). We envisage a scenario in

which content can be uploaded in the cabin infrastructure by means of the satellite system unlike

nowadays. Indeed, as of today, media content for passengers is loaded into the central media servers when

aircrafts are grounded whereby a time-consuming process (several hours). In addition, the existing content

loading procedure restricts to deploy a single media catalogue on-board, which is changed or updated in a

relatively long period of time (weeks or months). However, not all media contents that are deployed on-

board have the same popularity and, sometimes, volatile content (e.g. video clip) that is shared in

conjunction of specific events may become viral. An example is provided by major sport events or popular

events like the Academy awards. In such context, airlines might want to update their media catalogue on

certain routes or even create a second catalogue where viral clips with a short timespan can be cached. An

edge cloud deployed on-board the aircraft can be used to locally deploy a subset of the virtualized 5G

mobile core functionalities. In the bear minimum case a UPF function can be deployed to enable access to

the local data content network such as the secondary catalogue mentioned above.

Figure 23: End-to-end connectivity scenario in content service for aircrafts through satellite-terrestrial integration

SummarySummarySummarySummary

The research pillar I “Implementing 5G SDN and NFV in Satellite Networks” has studied a hybrid satellite /

5G network, relying on 5G SDN-capable satellite VNFs, and an Orchestrator based on the Open Source

MANO (OSM) to achieve an automated deployment of satellite network services. Implementing such

solution in a 5GIC test-bed, with iDirect satcom equipment and testing over Avanti HYLAS GEO capacity,

proved that virtualization in satellite network is viable, and it should improve the integration of space

segment into 5G systems and reduce the cost, making use of 5G COTS (Commercial Off-The-Shelf)

components.

The research pillar II “Integrated Network Management and Orchestration” focused on the extension of the

3GPP framework by including satellite elements, i.e. satellite VNFs (e.g. propagation impairments


SaT5G whitepaper

mitigation VNF for the satellite ground gateway), satellite PNFs (Radio Physical Network Functions) and

satellite DM (Domain Manager) including satellite EMs (Radio Element Managers). This pillar helped to

design and develop the TALENT coordination product, which supports end-to-end services setting up,

provisioning required resources such as satellite, radio access, cloud and mobile edge computing and

interfacing with 5G applications. The Zodiac Inflight Innovation test-bed with Gilat satcom equipment and

SES’s O3B MEO capacity, proved that the flexibility, the agnostics characteristics of TALENT, position this

product to build terrestrial, satellite and hybrid networks management and orchestration solutions,

simplifying operations and processes, for the benefits of vendors and operators.

The research pillar III “Multi-link and Heterogeneous Transport” proved that providing multiple terrestrial

and space paths with different characteristics of latency and bandwidth, and using multi-path protocols

such as MPTCP or MPQUIC, with a relevant Path Selection Algorithm, it is possible to enhance the user’s

Quality of Experience, by improving the throughput, increasing the fault tolerance, preventing from

congestion and reducing the delay for sensitive-latency user services. This pillar led to a proposal

enhancement of 3GPP AT3S (Access Traffic Steering, Switching, and Splitting) [37], in the context of SA2

study item.

The research pillar IV “Harmonisation of satcom with 5G Control and User Planes” studied possible

adaptations of the NR radio interface to implement it on satellite user link and face SATCOM constraints

such as Doppler shift, Doppler rate due to the satellite moving, longer propagation delay, due to the

satellite altitude, lower SNR (Signal To Noise Ratio) due to the attenuations across the atmosphere, signal

distortion and PAPR effects in the satellite payload, time alignment impairments due to high differential

delay between UE under satellite coverture, both at Random Access Process and during TA adjustment . All

these issues have not been taken into account in the initial design of the terrestrial NR radio interface and

needs appropriate responses / solutions. This research pillar published several scientific papers [32], [34]

and mainly contributed to 3GPP TR 38.811 [35], which identified classes of issues for adapting NR interface.

This research pillar also characterized the potential impacts of longer delay on UE-Core Network interface,

NTN (Non-terrestrial Network) gNB – Core Network interface and associated protocol layers.

The research pillar V “Extending 5G Security to Satellites” focused on access control of modem and

terminals, protection of the forward and return links, at transmission level, and access control to satellite

gateways, management systems of space and ground segments, per integration scenario basis. This pillar

led to several conclusions or recommendations, which are helpful for any implementation, as a guide line:

• IPSec tunnels as required in 3GPP for backhauling over an untrusted satellite transport network, set

between a terrestrial RAN and the Core Network, cannot be optimally used as is. It requires TCP

acceleration outside the IPsec tunnel.

• For satellite access network providing a direct access to UE, relevant 3GPP mechanisms can be fully

applied, according to the status of the satellite network which can be considered either as a trusted or

an untrusted 3GPP access by the MNO. A satellite network providing a non-3GPP access, if considered

as trusted, would simplify security procedures.

• In particular, the extra delays caused by satellite connections have no expected impact on the current

3GPP security procedures. But the security procedures over-the-air could be re-enforced, when

needed.


SaT5G whitepaper

• However, cooperation between MNOs and SNOs is required, which could rely on virtualization

mechanisms, per network slicing basis, for example.

The research Pillar VI “Caching & Multicast for Optimized Content & VNF distribution” first studied the

benefits of caching popular content, multicast by satellite during off-peak period towards 5G mobile

network edges. These methods can enhance the user QoE, regarding the traditional media streaming and

should also reduce the backhaul content traffic over the Core Network, during these periods. This research

pillar then proved the feasibility of using multicast adaptive bitrate streaming over satellite as contribution

to deliver a 4K/4K+ video content in real-time, to a MEC (multi-access edge computing) server, from the 5G

core. In order to do so, pre-fetching techniques were used and protocol such as DASH (Dynamic Adaptive

Streaming over HTTP) was adapted to face longer latency on satellite link. The pillar also developed

techniques for efficient splitting video content segments to be delivered over parallel terrestrial and

satellite backhauls, to enhance the QoE of the video sessions, in a 5G multi-link environment. As a further

PoC (Proof of Concept), media content could be uploaded in the airborne aircrafts through a satellite-

enabled 5G network.

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H2020-ICT-2016-2017/H2020-ICT-2016-2".

[4] ETSI, "SESSCN(18)000020)/ETSI SCN TC-SES - DTR/SES-00405 - TR 103 611 / Satellite Earth Stations and

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5G and related architecture options," 2019.

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[11] P. S. Khodashenas, H. Khalili, D. Guija and M. S. Siddiqui, "TALENT: Towards Integration of Satellite and

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integrating satcom and 5g: challenges and solutions

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