rfc9372.original.xml   rfc9372.xml 
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<front> <front>
<title abbrev='LDACS'>L-band Digital Aeronautical Communications System <title abbrev='LDACS'>L-Band Digital Aeronautical Communications System
(LDACS)</title> (LDACS)</title>
<seriesInfo name="RFC" value="9372"/>
<author fullname="Nils Mäurer" initials="N." <author fullname="Nils Mäurer" initials="N."
surname="Mäurer" role="editor"> surname="Mäurer" role="editor">
<organization>German Aerospace Center (DLR)</organization> <organization>German Aerospace Center (DLR)</organization>
<address> <address>
<postal> <postal>
<street ascii="Muenchner Strasse 20">Münchner Strasse 20</st <street> Münchner Strasse 20</street>
reet>
<!-- Reorder these if your country does things differently -
->
<code>82234</code> <code>82234</code>
<city ascii="Wessling">Wessling</city> <city>Wessling</city>
<region></region> <region></region>
<country>Germany</country> <country>Germany</country>
</postal> </postal>
<!--<phone></phone>-->
<email>Nils.Maeurer@dlr.de</email> <email>Nils.Maeurer@dlr.de</email>
<!-- uri and facsimile elements may also be added -->
</address> </address>
</author> </author>
<author fullname="Thomas Gräupl" initials="T."
<!--role="editor"-->
<author fullname="Thomas Gräupl" initials="T."
surname="Gräupl" role="editor"> surname="Gräupl" role="editor">
<organization>German Aerospace Center (DLR)</organization> <organization>German Aerospace Center (DLR)</organization>
<address> <address>
<postal> <postal>
<street ascii="Muenchner Strasse 20">Münchner Strasse 20</st <street>Münchner Strasse 20</street>
reet>
<!-- Reorder these if your country does things differently -
->
<code>82234</code> <code>82234</code>
<city ascii="Wessling">Wessling</city> <city>Wessling</city>
<region></region> <region></region>
<country>Germany</country> <country>Germany</country>
</postal> </postal>
<!--<phone></phone>-->
<email>Thomas.Graeupl@dlr.de</email> <email>Thomas.Graeupl@dlr.de</email>
<!-- uri and facsimile elements may also be added -->
</address> </address>
</author> </author>
<author fullname="Corinna Schmitt" initials="C." <author fullname="Corinna Schmitt" initials="C."
surname="Schmitt" role="editor"> surname="Schmitt" role="editor">
<organization>Research Institute CODE, UniBwM</organization> <organization>Research Institute CODE, UniBwM</organization>
<address> <address>
<postal> <postal>
<street>Werner-Heisenberg-Weg 39</street> <street>Werner-Heisenberg-Weg 39</street>
<!-- Reorder these if your country does things differently - ->
<code>85577</code> <code>85577</code>
<city>Neubiberg</city> <city>Neubiberg</city>
<region></region> <region></region>
<country>Germany</country> <country>Germany</country>
</postal> </postal>
<!--<phone></phone>-->
<email>corinna.schmitt@unibw.de</email> <email>corinna.schmitt@unibw.de</email>
<!-- uri and facsimile elements may also be added -->
</address> </address>
</author> </author>
<date year="2023" month="March" />
<date/> <area>rtg</area>
<workgroup>raw</workgroup>
<area>Routing</area>
<workgroup>RAW</workgroup>
<abstract> <abstract>
<t> This document gives an overview of the architecture of the L-ban d Digital Aeronautical Communications System (LDACS), which provides a secure, s calable and spectrum efficient terrestrial data link for civil aviation. LDACS is a scheduled, reliable multi-application cellular broadband system with suppor t for IPv6. It is part of a larger shift of flight guidance communication moving to IP-based communication. High reliability and availability of IP connectivity over LDACS, as well as security, are therefore essential. The intent of this do cument is to introduce LDACS to the IETF community, raise awareness on related a ctivities inside and outside of the IETF, and to seek expertise in shaping the s hift of aeronautics to IP. <t> This document gives an overview of the L-band Digital Aeronautic al Communications System (LDACS) architecture, which provides a secure, scalable , and spectrum-efficient terrestrial data link for civil aviation. LDACS is a s cheduled and reliable multi-application cellular broadband system with support f or IPv6. It is part of a larger shift of flight guidance communication moving to IP-based communication. High reliability and availability of IP connectivity ov er LDACS, as well as security, are therefore essential. The intent of this docum ent is to introduce LDACS to the IETF community, raise awareness on related acti vities inside and outside of the IETF, and to seek expertise in shaping the shif t of aeronautics to IP.
</t> </t>
</abstract> </abstract>
</front> </front>
<middle> <middle>
<section><name>Introduction</name> <section><name>Introduction</name>
<t> <t>
One of the main pillars of the modern Air Traffic Management (AT One of the main pillars of the modern Air Traffic Management (AT
M) system is the existence of a communications infrastructure that enables effic M) system is the existence of a communications infrastructure that enables effic
ient aircraft control and safe aircraft separation in all phases of flight. Cur ient aircraft control and safe aircraft separation in all phases of flight. Cur
rent systems are technically mature but suffering from the Very High Frequency ( rent systems are technically mature, but they are suffering from the Very High F
VHF) band's increasing saturation in high-density areas and the limitations pose requency (VHF) band's increasing saturation in high-density areas and the limita
d by analogue radio communications. Therefore, aviation strives for a sustainab tions posed by analog radio communications. Therefore, aviation strives for a s
le modernization of the aeronautical communications infrastructure on the basis ustainable modernization of the aeronautical communications infrastructure on th
of IP. e basis of IP.
</t>
<t>
This modernization is realized in two steps: (1) the transition
of communications datalinks from analogue to digital technologies and, (2) the i
ntroduction of IPv6 based networking protocols <xref target="RFC8200"/> in aeron
autical networks <xref target="ICAO2015"/>.
</t> </t>
<t> <t>
Step (1) is realized via ATM communications transitioning from a This modernization is realized in two steps: (1) the transition
nalogue VHF voice <xref target="KAMA2010"/> to more spectrum efficient digital d of communications data links from analog to digital technologies and (2) the int
ata communication. For terrestrial communications the International Civil Aviat roduction of IPv6-based networking protocols <xref target="RFC8200"/> in aeronau
ion Organization (ICAO)'s Global Air Navigation Plan (GANP) foresees this transi tical networks <xref target="ICAO2015"/>.</t>
tion to be realized by the development of the L-band Digital Aeronautical Commun
ications System (LDACS). Since Central Europe has been identified as the area of <t>Step (1) is realized via ATM communications transitioning from an
the world that suffers the most from increased saturation of the VHF band, the alog VHF voice <xref target="KAMA2010"/> to more spectrum-efficient digital data
initial roll-out of LDACS will likely start there, and continue to other increas communication. For terrestrial communications, the Global Air Navigation Plan
ingly saturated zones as the East and West Coast of the US and parts of Asia <xr (GANP) created by the International Civil Aviation Organization (ICAO) foresees
ef target="ICAO2018"/>. this transition to be realized by the development of the L-band Digital Aeronaut
ical Communications System (LDACS). Since Central Europe has been identified as
the area of the world that suffers the most from increased saturation of the VHF
band, the initial rollout of LDACS will likely start there and continue to othe
r increasingly saturated zones such as the East and West Coast of the US and par
ts of Asia <xref target="ICAO2018"/>.
</t> </t>
<t> <t>
Technically LDACS enables IPv6-based air-ground communication re Technically, LDACS enables IPv6-based Air/Ground (A/G) communica
lated to aviation safety and regularity of flight <xref target="ICAO2015"/>. Pas tion related to aviation safety and regularity of flight <xref target="ICAO2015"
senger communication and similar services are not supported, since only communic />. Passenger communication and similar services are not supported since only co
ations related to "safety and regularity of flight" are permitted in protected a mmunications related to "safety and regularity of flight" are permitted in prote
viation frequency bands. The particular challenge is that no additional frequenc cted aviation frequency bands.
ies can be made available for terrestrial aeronautical communication. It was thu The particular challenge is that no additional frequencies can be made available
s necessary to develop co-existence mechanism/procedures to enable the interfere for terrestrial aeronautical communication; thus, it was necessary to develop c
nce free operation of LDACS in parallel with other aeronautical services/systems oexistence mechanisms and procedures to enable the interference-free operation o
in the protected frequency band. Since LDACS will be used for aircraft guidance f LDACS in parallel with other aeronautical services and systems in the protecte
, high reliability and availability for IP connectivity over LDACS are essential d frequency band. Since LDACS will be used for aircraft guidance, high reliabili
. ty and availability for IP connectivity over LDACS are essential.
</t> </t>
<t> <t>
LDACS is standardized in ICAO and European Organization for Civi l Aviation Equipment (EUROCAE). LDACS is standardized in ICAO and the European Organization for Civil Aviation Equipment (EUROCAE).
</t> </t>
<t> <t>
This document provides information to the IETF community about t he aviation industry transition of flight guidance systems from analog to digita l, provides context for LDACS relative to related IETF activities <xref target= "I-D.haindl-lisp-gb-atn" format="default"/>, and seeks expertise on realizing re liable IPv6 over LDACS for step (1). This document does not intend to advance LD ACS as an IETF standards-track document. This document provides information to the IETF community about t he aviation industry transition of flight guidance systems from analog to digita l, provides context for LDACS relative to related IETF activities <xref target= "I-D.haindl-lisp-gb-atn" format="default"/>, and seeks expertise on realizing re liable IPv6 over LDACS for step (1). This document does not intend to advance LD ACS as an IETF Standards Track document.
</t> </t>
<t> <t>
Step (2) is a strategy for the worldwide roll-out of IPv6 capabl Step (2) is a strategy for the worldwide rollout of IPv6-capable
e digital aeronautical inter-networking. This is called the Aeronautical Teleco digital aeronautical internetworking. This is called the Aeronautical Telecomm
mmunications Network (ATN)/Internet Protocol Suite (IPS) (hence, ATN/IPS). It i unications Network (ATN) / Internet Protocol Suite (IPS) (hence, ATN/IPS).
s specified in the International Civil Aviation Organization (ICAO) document Doc
9896 <xref target="ICAO2015"/>, the Radio Technical Commission for Aeronautics It is specified in the ICAO document Doc 9896 <xref target="ICAO2015"/>, the Rad
(RTCA) document DO-379 <xref target="RTCA2019"/>, the EUROCAE document ED-262 io Technical Commission for Aeronautics (RTCA) document DO-379 <xref target="RTC
<xref target="EURO2019"/>, and the Aeronautical Radio Incorporated (ARINC) docum A2019"/>, the EUROCAE document ED-262 <xref target="EURO2019"/>, and the Aeronau
ent P858 <xref target="ARI2021"/>. LDACS is subject to these regulations since i tical Radio Incorporated (ARINC) document 858 <xref target="ARI2021"/>. LDACS is
t provides an "access network" - link-layer datalink - to the ATN/IPS. subject to these regulations since it provides an "access network" (link-layer
data link) to the ATN/IPS.
</t> </t>
<t> <t>
ICAO has chosen IPv6 as basis for the ATN/IPS mostly for histori cal reasons, since a previous architecture based on ISO/OSI protocols, the ATN/O SI, failed in the marketplace. ICAO has chosen IPv6 as a basis for the ATN/IPS mostly for histo rical reasons since a previous architecture based on ISO/OSI protocols (the ATN/ OSI) failed in the marketplace.
</t> </t>
<t> <t>
In the context of safety-related communications, LDACS will play In the context of safety-related communications, LDACS will play
a major role in future ATM. ATN/IPS datalinks will provide diversified terrest a major role in future ATM. ATN/IPS data links will provide diversified terres
rial and space-based connectivity in a multilink concept, called the Future Comm trial and space-based connectivity in a multilink concept called the Future Comm
unications Infrastructure (FCI) <xref target="VIR2021"/>. From a technical poin unications Infrastructure (FCI) <xref target="VIR2021"/>. From a technical point
t of view the FCI will realize airborne multi-homed IPv6 networks connected to a of view, the FCI will realize airborne and multihomed IPv6 networks connected t
global ground network via at least two independent communication technologies. o a global ground network via at least two independent communication technologie
This is considered in more detail in related IETF work in progress <xref target s.
="I-D.haindl-lisp-gb-atn" format="default"/> <xref target="I-D.ietf-rtgwg-atn-bg This is considered in more detail in related IETF documents <xref target="I-D.ha
p" format="default"/>. As such, ICAO has actively sought out the support of IETF indl-lisp-gb-atn" format="default"/> <xref target="I-D.ietf-rtgwg-atn-bgp" forma
to define a mobility solution for step (2), which is currently the Locator/ID S t="default"/>. As such, ICAO has actively sought out the support of IETF to defi
eparation Protocol (LISP). ne a mobility solution for step (2), which is currently the Locator/ID Separatio
n Protocol (LISP).
</t> </t>
<t> <t>
In the context of the Reliable and Available Wireless (RAW) work ing group, developing options, such as intelligent switching between datalinks, for reliably delivering content from and to endpoints, is foreseen. As LDACS is part of such a concept, the work of RAW is immediately applicable. In general, with the aeronautical communications system transitioning to ATN/IPS, and data being transported via IPv6, closer cooperation and collaboration between the aer onautical and IETF community is desirable. In the context of the Reliable and Available Wireless (RAW) Work ing Group, developing options, such as intelligent switching between data links, for reliably delivering content from and to endpoints is foreseen. As LDACS is part of such a concept, the work of RAW is immediately applicable. In general, with the aeronautical communications system transitioning to ATN/IPS and data b eing transported via IPv6, closer cooperation and collaboration between the aero nautical and IETF community is desirable.
</t> </t>
<t> <t>
LDACS standardization within the framework of ICAO started in De LDACS standardization within the framework of ICAO started in De
cember 2016. The ICAO standardization group has produced the final Standards an cember 2016. As of 2022, the ICAO standardization group has produced the final
d Recommended Practices (SARPS) document as of 2022 <xref target="ICAO2022"/>. I Standards and Recommended Practices (SARPS) document <xref target="ICAO2022"/> t
t defines the general characteristics of LDACS. By the end of 2023, the ICAO sta hat defines the general characteristics of LDACS.
ndardization group plans to have developed an ICAO technical manual - the ICAO e
quivalent to a technical standard. As such LDACS standardization is not finishe By the end of 2023, the ICAO standardization group plans to have developed an IC
d yet, and therefore this document is a snapshot of current status. The physical AO technical manual, which is the ICAO equivalent to a technical standard. The
characteristics of an LDACS installation (form, fit, and function) will be stan LDACS standardization is not finished yet; therefore, this document is a snapsho
dardized by EUROCAE. Generally, the group is open to input from all sources and t of the current status. The physical characteristics of an LDACS installation (
encourages cooperation between the aeronautical and the IETF community. form, fit, and function) will be standardized by EUROCAE. Generally, the group i
s open to input from all sources and encourages cooperation between the aeronaut
ical and IETF communities.
</t> </t>
</section> </section>
<section><name>Acronyms</name> <section><name>Acronyms</name>
<t> <t>
The following terms are used in the context of RAW in this d ocument: The following terms are used in the context of RAW in this d ocument:
</t><dl spacing='compact'> </t><dl spacing='compact' indent='13'>
<dt>A/A</dt><dd> <dt>A/A:</dt><dd>
Air/Air Air/Air
</dd> </dd>
<dt>A/G</dt><dd> <dt>A/G:</dt><dd>
Air/Ground Air/Ground
</dd> </dd>
<dt>A2G</dt><dd> <dt>A2G:</dt><dd>
Air-to-Ground Air-to-Ground
</dd> </dd>
<dt>ACARS</dt><dd> <dt>ACARS:</dt><dd>
Aircraft Communications Addressing and Reporting Sys tem Aircraft Communications Addressing and Reporting Sys tem
</dd> </dd>
<dt>AC-R</dt><dd> <dt>AC-R:</dt><dd>
Access Router Access Router
</dd> </dd>
<dt>ADS-B</dt><dd> <dt>ADS-B:</dt><dd>
Automatic Dependent Surveillance - Broadcast Automatic Dependent Surveillance - Broadcast
</dd> </dd>
<dt>ADS-C</dt><dd> <dt>ADS-C:</dt><dd>
Automatic Dependent Surveillance – Contract Automatic Dependent Surveillance - Contract
</dd> </dd>
<dt>AeroMACS</dt><dd> <dt>AeroMACS:</dt><dd>
Aeronautical Mobile Airport Communications System Aeronautical Mobile Airport Communications System
</dd> </dd>
<dt>ANSP</dt><dd> <dt>ANSP:</dt><dd>
Air Traffic Network Service Provider Air Traffic Network Service Provider
</dd> </dd>
<dt>AOC</dt><dd> <dt>AOC:</dt><dd>
Aeronautical Operational Control Aeronautical Operational Control
</dd> </dd>
<dt>ARINC</dt><dd> <dt>ARINC:</dt><dd>
Aeronautical Radio, Incorporated Aeronautical Radio Incorporated
</dd> </dd>
<dt>ARQ</dt><dd> <dt>ARQ:</dt><dd>
Automatic Repeat reQuest Automatic Repeat reQuest
</dd> </dd>
<dt>AS</dt><dd> <dt>AS:</dt><dd>
Aircraft Station Aircraft Station
</dd> </dd>
<dt>ATC</dt><dd> <dt>ATC:</dt><dd>
Air Traffic Control Air Traffic Control
</dd> </dd>
<dt>ATM</dt><dd> <dt>ATM:</dt><dd>
Air Traffic Management Air Traffic Management
</dd> </dd>
<dt>ATN</dt><dd> <dt>ATN:</dt><dd>
Aeronautical Telecommunication Network Aeronautical Telecommunications Network
</dd> </dd>
<dt>ATS</dt><dd> <dt>ATS:</dt><dd>
Air Traffic Service Air Traffic Service
</dd> </dd>
<dt>BCCH</dt><dd> <dt>BCCH:</dt><dd>
Broadcast Channel Broadcast Channel
</dd> </dd>
<dt>CCCH</dt><dd> <dt>CCCH:</dt><dd>
Common Control Channel Common Control Channel
</dd> </dd>
<dt>CM</dt><dd> <dt>CM:</dt><dd>
Context Management Context Management
</dd> </dd>
<dt>CNS</dt><dd> <dt>CNS:</dt><dd>
Communication Navigation Surveillance Communication Navigation Surveillance
</dd> </dd>
<dt>COTS</dt><dd> <dt>COTS:</dt><dd>
Commercial Off-The-Shelf Commercial Off-The-Shelf
</dd> </dd>
<dt>CPDLC</dt><dd> <dt>CPDLC:</dt><dd>
Controller Pilot Data Link Communications Controller-Pilot Data Link Communications
</dd>
<dt>CRL</dt><dd>
Certificate Revocation List
</dd> </dd>
<dt>CSP</dt><dd> <dt>CSP:</dt><dd>
Communications Service Provider Communications Service Provider
</dd> </dd>
<dt>DCCH</dt><dd> <dt>DCCH:</dt><dd>
Dedicated Control Channel Dedicated Control Channel
</dd> </dd>
<dt>DCH</dt><dd> <dt>DCH:</dt><dd>
Data Channel Data Channel
</dd> </dd>
<dt>DiffServ</dt><dd> <dt>Diffserv:</dt><dd>
Differentiated Services Differentiated Services
</dd> </dd>
<dt>DLL</dt><dd> <dt>DLL:</dt><dd>
Data Link Layer Data Link Layer
</dd> </dd>
<dt>DLS</dt><dd> <dt>DLS:</dt><dd>
Data Link Service Data Link Service
</dd> </dd>
<dt>DME</dt><dd> <dt>DME:</dt><dd>
Distance Measuring Equipment Distance Measuring Equipment
</dd> </dd>
<dt>DSB-AM</dt><dd> <dt>DSB-AM:</dt><dd>
Double Side-Band Amplitude Modulation Double Side-Band Amplitude Modulation
</dd> </dd>
<dt>DTLS</dt><dd> <dt>DTLS:</dt><dd>
Datagram Transport Layer Security Datagram Transport Layer Security
</dd> </dd>
<dt>EUROCAE</dt><dd> <dt>EUROCAE:</dt><dd>
European Organization for Civil Aviation Equipment European Organization for Civil Aviation Equipment
</dd> </dd>
<dt>FAA</dt><dd> <dt>FAA:</dt><dd>
Federal Aviation Administration Federal Aviation Administration
</dd> </dd>
<dt>FCI</dt><dd> <dt>FCI:</dt><dd>
Future Communications Infrastructure Future Communications Infrastructure
</dd> </dd>
<dt>FDD</dt><dd> <dt>FDD:</dt><dd>
Frequency Division Duplex Frequency Division Duplex
</dd> </dd>
<dt>FL</dt><dd> <dt>FL:</dt><dd>
Forward Link Forward Link
</dd> </dd>
<dt>GANP</dt><dd> <dt>GANP:</dt><dd>
Global Air Navigation Plan Global Air Navigation Plan
</dd> </dd>
<dt>GBAS</dt><dd> <dt>GBAS:</dt><dd>
Ground Based Augmentation System Ground-Based Augmentation System
</dd> </dd>
<dt>GNSS</dt><dd> <dt>GNSS:</dt><dd>
Global Navigation Satellite System Global Navigation Satellite System
</dd> </dd>
<dt>GS</dt><dd> <dt>GS:</dt><dd>
Ground-Station Ground-Station
</dd> </dd>
<dt>G2A</dt><dd> <dt>G2A:</dt><dd>
Ground-to-Air Ground-to-Air
</dd> </dd>
<dt>HF</dt><dd> <dt>HF:</dt><dd>
High Frequency High Frequency
</dd> </dd>
<dt>ICAO</dt><dd> <dt>ICAO:</dt><dd>
International Civil Aviation Organization International Civil Aviation Organization
</dd> </dd>
<dt>IP</dt><dd> <dt>IP:</dt><dd>
Internet Protocol Internet Protocol
</dd> </dd>
<dt>IPS</dt><dd> <dt>IPS:</dt><dd>
Internet Protocol Suite Internet Protocol Suite
</dd> </dd>
<dt>kbit/s</dt><dd> <dt>kbit/s:</dt><dd>
kilobit per second kilobit per second
</dd> </dd>
<dt>LDACS</dt><dd> <dt>LDACS:</dt><dd>
L-band Digital Aeronautical Communications System L-band Digital Aeronautical Communications System
</dd> </dd>
<dt>LISP</dt><dd> <dt>LISP:</dt><dd>
Locator/ID Separation Protocol Locator/ID Separation Protocol
</dd> </dd>
<dt>LLC</dt><dd> <dt>LLC:</dt><dd>
Logical Link Control Logical Link Control
</dd> </dd>
<dt>LME</dt><dd> <dt>LME:</dt><dd>
LDACS Management Entity LDACS Management Entity
</dd> </dd>
<dt>MAC</dt><dd> <dt>MAC:</dt><dd>
Medium Access Control Medium Access Control
</dd> </dd>
<dt>MF</dt><dd> <dt>MF:</dt><dd>
Multi Frame Multiframe
</dd> </dd>
<dt>NETCONF</dt><dd> <dt>NETCONF:</dt><dd>
NETCONF Network Configuration Protocol Network Configuration Protocol
</dd> </dd>
<dt>OFDM</dt><dd> <dt>OFDM:</dt><dd>
Orthogonal Frequency-Division Multiplexing Orthogonal Frequency Division Multiplexing
</dd> </dd>
<dt>OFDMA</dt><dd> <dt>OFDMA:</dt><dd>
Orthogonal Frequency-Division Multiplexing Access Orthogonal Frequency Division Multiplexing Access
</dd> </dd>
<dt>OSI</dt><dd> <dt>OSI:</dt><dd>
Open Systems Interconnection Open Systems Interconnection
</dd> </dd>
<dt>PHY</dt><dd> <dt>PHY:</dt><dd>
Physical Layer Physical Layer
</dd> </dd>
<dt>QPSK</dt><dd> <dt>QPSK:</dt><dd>
Quadrature Phase-Shift Keying Quadrature Phase-Shift Keying
</dd> </dd>
<dt>RACH</dt><dd> <dt>RACH:</dt><dd>
Random-Access Channel Random-Access Channel
</dd> </dd>
<dt>RL</dt><dd> <dt>RL:</dt><dd>
Reverse Link Reverse Link
</dd> </dd>
<dt>RTCA</dt><dd> <dt>RTCA:</dt><dd>
Radio Technical Commission for Aeronautics Radio Technical Commission for Aeronautics
</dd> </dd>
<dt>SARPS</dt><dd> <dt>SARPS:</dt><dd>
Standards and Recommended Practices Standards and Recommended Practices
</dd> </dd>
<dt>SDR</dt><dd> <dt>SDR:</dt><dd>
Software Defined Radio Software-Defined Radio
</dd> </dd>
<dt>SESAR</dt><dd> <dt>SESAR:</dt><dd>
Single European Sky ATM Research Single European Sky ATM Research
</dd> </dd>
<dt>SF</dt><dd> <dt>SF:</dt><dd>
Super-Frame Super-Frame
</dd> </dd>
<dt>SNMP</dt><dd> <dt>SNMP:</dt><dd>
Simple Network Management Protocol Simple Network Management Protocol
</dd> </dd>
<dt>SNP</dt><dd>
Sub-Network Protocol <dt>SNP:</dt><dd>
Subnetwork Protocol
</dd> </dd>
<dt>VDLm2</dt><dd> <dt>VDLm2:</dt><dd>
VHF Data Link mode 2 VHF Data Link mode 2
</dd> </dd>
<dt>VHF</dt><dd> <dt>VHF:</dt><dd>
Very High Frequency Very High Frequency
</dd> </dd>
<dt>VI</dt><dd> <dt>VI:</dt><dd>
Voice Interface Voice Interface
</dd> </dd>
</dl><t> </dl><t>
</t> </t>
</section> </section>
<section anchor='MotivationUC'><name>Motivation and Use Cases</name> <section anchor='MotivationUC'><name>Motivation and Use Cases</name>
<t> <t>
Aircraft are currently connected to Air Traffic Control (ATC) an Aircraft are currently connected to Air Traffic Control (ATC) an
d Aeronautical Operational Control (AOC) services via voice and data communicati d Aeronautical Operational Control (AOC) services via voice and data communicati
ons systems through all phases of flight. ATC refers to communication for fligh ons systems through all phases of flight. ATC refers to communication for fligh
t guidance. AOC is a generic term referring to the business communication of ai t guidance. AOC is a generic term referring to the business communication of ai
rlines. It refers to the mostly proprietary exchange of data between the aircraf rlines and refers to the mostly proprietary exchange of data between the aircraf
t of the airline and the airline's operation centers and service partners. The A t of the airline and the airline's operation centers and service partners.
RINC document 633 was developed and first released in 2007 <xref target="ARI2019 The ARINC document 633 was developed and first released in 2007 <xref target="AR
"/> with the goal to standardize these messages for interoperability, e.g., mess I2019"/> with the goal to standardize these messages for interoperability, e.g.,
ages between the airline and fueling or de-icing companies. Within the airport a messages between the airline and fueling or de-icing companies. Within the airp
nd terminal area, connectivity is focused on high bandwidth communications. In ort and terminal area, connectivity is focused on high bandwidth communications.
the En-Route domain, however, high reliability, robustness, and range are the ma However, in the en route domain, high reliability, robustness, and range are t
in foci. Voice communications may use the same or different equipment as data c he main foci. Voice communications may use the same or different equipment as d
ommunications systems. In the following, the main differences between voice and ata communications systems. In the following, the main differences between voice
data communications capabilities are summarized. The assumed list of use cases and data communications capabilities are summarized. The assumed list of use c
for LDACS complements the list of use cases stated in <xref target="I-D.ietf-raw ases for LDACS complements the list of use cases stated in <xref target="I-D.iet
-use-cases" format="default"/> and the list of reliable and available wireless t f-raw-use-cases" format="default"/> and the list of reliable and available wirel
echnologies presented in <xref target="I-D.ietf-raw-technologies" format="defaul ess technologies presented in <xref target="I-D.ietf-raw-technologies" format="d
t"/>. efault"/>.
</t> </t>
<section anchor='VoiceCom'><name>Voice Communications Today</name> <section anchor='VoiceCom'><name>Voice Communications Today</name>
<t> <t>
Voice links are used for Air/Ground (A/G) and Air/Air (A/A) communications. The communications equipment can be installed on ground or in t he aircraft, in which cases the High Frequency (HF) or VHF frequency band is use d. For remote domains voice communications can also be satellite-based. All VHF and HF voice communications are operated via open broadcast channels without au thentication, encryption or other protective measures. The use of well-proven co mmunications procedures via broadcast channels, such as phraseology or read-back s, requiring well-trained personnel, help to enhance the safety of communicati ons, but does not replace necessary cryptographical security mechanisms. The mai n voice communications media is still the analogue VHF Double Side-Band Amplitud e Modulation (DSB-AM) communications technique, supplemented by HF single side-b and amplitude modulation and satellite communications for remote and oceanic reg ions. DSB-AM has been in use since 1948, works reliably and safely, and uses lo w-cost communication equipment. These are the main reasons why VHF DSB-AM commu nications are still in use, and it is likely that this technology will remain in service for many more years. This however, results in current operational limi tations and impediments in deploying new ATM applications, such as flight-centri c operation with point-to-point communications between pilots and air traffic co ntrol officers. <xref target="BOE2019"/> Voice links are used for Air/Ground (A/G) and Air/Air (A/A) communications. The communications equipment can be installed on ground or in t he aircraft, in which cases the High Frequency (HF) or VHF frequency band is use d. For remote domains, voice communications can also be satellite-based. All VH F and HF voice communications are operated via open Broadcast Channels (BCCHs) w ithout authentication, encryption, or other protective measures. The use of well -proven communications procedures via BCCHs, such as phraseology or read-backs, requiring well-trained personnel help to enhance the safety of communications bu t does not replace necessary cryptographical security mechanisms. The main voice communications media is still the analog VHF Double Side-Band Amplitude Modulat ion (DSB-AM) communications technique supplemented by HF single side-band amplit ude modulation and satellite communications for remote and oceanic regions. DSB -AM has been in use since 1948, works reliably and safely, and uses low-cost com munication equipment. These are the main reasons why VHF DSB-AM communications are still in use, and it is likely that this technology will remain in service f or many more years. However, this results in current operational limitations an d impediments in deploying new ATM applications, such as flight-centric operatio n with point-to-point communications between pilots and ATC officers <xref targe t="BOE2019"/>.
</t> </t>
</section> </section>
<section anchor='DataCom'><name>Data Communications Today</name> <section anchor='DataCom'><name>Data Communications Today</name>
<t> <t>
Like for voice, data communications into the cockpit, are cu Like for voice communications, data communications into the
rrently provided by ground-based equipment operating either on HF or VHF radio b cockpit are currently provided by ground-based equipment operating either on HF
ands or by legacy satellite systems. All these communication systems use narrow or VHF radio bands or by legacy satellite systems. All these communication syst
band radio channels with a data throughput capacity in the order of kbit/s. Whi ems use narrowband radio channels with a data throughput capacity in the order o
le the aircraft is on the ground, some additional communications systems are ava f kbit/s.
ilable, like the Aeronautical Mobile Airport Communications System (AeroMACS) or Additional communications systems are available while the aircraft is on the gro
public cellular networks, operating in the Airport (APT) domain and able to del und, such as the Aeronautical Mobile Airport Communications System (AeroMACS) or
iver broadband communications capability. <xref target="BOE2019"/> public cellular networks, that operate in the Airport (APT) domain and are able
to deliver broadband communications capability <xref target="BOE2019"/>.
</t> </t>
<t> <t>
For regulatory reasons, the data communications networks, us For regulatory reasons, the data communications networks use
ed for the transmission of data relating to the safety and regularity of flight, d for the transmission of data relating to the safety and regularity of flight m
must be strictly isolated from those providing entertainment services to passen ust be strictly isolated from those providing entertainment services to passenge
gers. This leads to a situation that the flight crews are supported by narrowban rs. This leads to a situation where the flight crews are supported by narrowband
d services during flight while passengers have access to inflight broadband serv services during flight while passengers have access to in-flight broadband serv
ices. The current HF and VHF data links cannot provide broadband services now o ices. The current HF and VHF data links cannot provide broadband services now or
r in the future, due to the lack of available spectrum. This technical shortcom in
ing is becoming a limitation to enhanced ATM operations, such as trajectory-base the future due to the lack of available spectrum. This technical shortcoming
d operations and 4D trajectory negotiations. <xref target="BOE2019"/> is becoming a limitation to enhanced ATM operations, such as trajectory-based
operations and 4D trajectory negotiations <xref target="BOE2019"/>.
</t> </t>
<t> <t>
Satellite-based communications are currently under investiga Satellite-based communications are currently under
tion and enhanced capabilities are under development which will be able to provi investigation, and enhanced capabilities that will
de inflight broadband services and communications supporting the safety and regu be able to provide in-flight
larity of flight. In parallel the ground-based broadband data link technology LD broadband services and communications supporting the
ACS is being standardized by ICAO and has recently shown its maturity during fli safety and regularity of flight are under
ght tests <xref target="MAE20211"/> <xref target="BEL2021"/>. The LDACS technolo development. In parallel, the
gy is scalable, secure and spectrum efficient and provides significant advantage ground-based broadband data link technology LDACS is being
s to the users and service providers. It is expected that both - satellite syste standardized by ICAO and has recently shown its maturity
ms and LDACS - will be deployed to support the future aeronautical communication during flight tests <xref target="MAE20211"/> <xref
needs as envisaged by the ICAO Global Air Navigation Plan (GNAP). <xref target= target="BEL2021"/>. The LDACS technology is scalable,
"BOE2019"/> secure, and spectrum-efficient, and it provides significant
advantages to the users and service providers. It is
expected that both satellite systems and LDACS will be
deployed to support the future aeronautical communication
needs as envisaged by the ICAO GANP <xref target="BOE2019"/>
.
</t> </t>
</section> </section>
</section> </section>
<section anchor='ProvenanceandDocuments'><name>Provenance and Documents< /name> <section anchor='ProvenanceandDocuments'><name>Provenance and Documents< /name>
<t> <t>
The development of LDACS has already made substantial progress i n the Single European Sky ATM Research (SESAR) framework and is currently being continued in the follow-up program SESAR2020 <xref target="RIH2018"/>. A key obj ective of these activities is to develop, implement and validate a modern aerona utical data link able to evolve with aviation needs over the long term. To this end, an LDACS specification has been produced <xref target="GRA2020"/> and is co ntinuously updated; transmitter demonstrators were developed to test the spectru m compatibility of LDACS with legacy systems operating in the L-band <xref targe t="SAJ2014"/>; and the overall system performance was analyzed by computer simul ations, indicating that LDACS can fulfil the identified requirements <xref targe t="GRA2011"/>. The development of LDACS has already made substantial progress i n the Single European Sky ATM Research (SESAR) framework and is currently being continued in the follow-up program SESAR2020 <xref target="RIH2018"/>. A key obj ective of these activities is to develop, implement, and validate a modern aeron autical data link that is able to evolve with aviation needs over the long term. To this end, an LDACS specification has been produced <xref target="GRA2020"/> and is continuously updated. Transmitter demonstrators were developed to test th e spectrum compatibility of LDACS with legacy systems operating in the L-band <x ref target="SAJ2014"/>, and the overall system performance was analyzed by compu ter simulations, indicating that LDACS can fulfill the identified requirements < xref target="GRA2011"/>.
</t> </t>
<t> <t>
Up to now LDACS standardization has been focused on the developm ent of the physical layer and the data link layer. Only recently have higher la yers have come into the focus of the LDACS development activities. Currently no "IPv6 over LDACS" specification is defined; however, SESAR2020 has started expe rimenting with IPv6-based LDACS and ICAO plans to seek guidance from IETF to dev elop IPv6 over LDACS. As of May 2022, LDACS defines 1536 Byte user-data packets <xref target="GRA2020"/> in which IPv6 traffic shall be encapsulated. Additional ly, Robust Header Compression (ROHC) is considered on LDACS Sub-Network Protocol (SNP) layer (cf. Section 7.3.3.) <xref target="RFC5795"/>. Up to now, LDACS standardization has been focused on the develop ment of the Physical Layer (PHY) and the Data Link Layer (DLL). Only recently h ave higher layers come into the focus of the LDACS development activities. Curr ently no "IPv6 over LDACS" specification is defined; however, SESAR2020 has star ted experimenting with IPv6-based LDACS and ICAO plans to seek guidance from IET F to develop IPv6 over LDACS. As of May 2022, LDACS defines 1536-byte user data packets <xref target="GRA2020"/> in which IPv6 traffic shall be encapsulated. Ad ditionally, Robust Header Compression (ROHC) <xref target="RFC5795"/> is conside red on the LDACS Subnetwork Protocol (SNP) layer (cf.&nbsp;<xref target="SNPserv ice"/>).
</t> </t>
<t> <t>
The IPv6 architecture for the aeronautical telecommunication net work is called the ATN/IPS. Link-layer technologies within the ATN/IPS encompass LDACS <xref target="GRA2020"/>, AeroMACS <xref target="KAMA2018"/> and several SatCOM candidates and combined with the ATN/IPS, are called the FCI. The FCI wi ll support quality of service, link diversity, and mobility under the umbrella o f the "multilink concept". The "multilink concept" describing the idea that depe nding on link quality, communication can be switched seamlessly from one datalin k technology to another. This work is led by ICAO Communication Panel working gr oup WG-I. The IPv6 architecture for the aeronautical telecommunication network is called t he ATN/IPS. Link-layer technologies within the ATN/IPS encompass LDACS <xref tar get="GRA2020"/>, AeroMACS <xref target="KAMA2018"/>, and several SatCOM candidat es; combined with the ATN/IPS, these are called the "FCI". The FCI will support quality of service, link diversity, and mobility under the umbrella of the "mult ilink concept". The "multilink concept" describes the idea that depending on lin k quality, communication can be switched seamlessly from one data link technolog y to another. This work is led by the ICAO Communication Panel Working Group (WG -I).
</t> </t>
<t> <t>
In addition to standardization activities several industrial LDA CS prototypes have been built. One set of LDACS prototypes has been evaluated in flight trials confirming the theoretical results predicting the system performa nce <xref target="GRA2018"/> <xref target="MAE20211"/> <xref target="BEL2021"/>. In addition to standardization activities, several industrial LD ACS prototypes have been built. One set of LDACS prototypes has been evaluated i n flight trials confirming the theoretical results predicting the system perform ance <xref target="GRA2018"/> <xref target="MAE20211"/> <xref target="BEL2021"/> .
</t> </t>
</section> </section>
<section anchor='Applicability'><name>Applicability</name> <section anchor='Applicability'><name>Applicability</name>
<t> <t>
LDACS is a multi-application cellular broadband system capable o LDACS is a multi-application cellular broadband system capable o
f simultaneously providing various kinds of Air Traffic Services (ATS) including f simultaneously providing various kinds of Air Traffic Services (ATSs) includin
ATS-B3, and AOC communications services from deployed Ground-Stations (GS). Th g ATS-B3 and AOC communications services from deployed Ground-Stations (GSs).
e physical layer and data link layer of LDACS are optimized for controller-pilot
data link communications, but the system also supports digital air-ground voice The physical layer and data link layer of LDACS are optimized for Controller-Pil
communications. ot Data Link Communications (CPDLC), but the system also supports digital A/G vo
ice communications.
</t> </t>
<t> <t>
LDACS supports communications in all airspaces (airport, termina l maneuvering area, and en-route), and on the airport surface. The physical LDA CS cell coverage is effectively de-coupled from the operational coverage require d for a particular service. This is new in aeronautical communications. Servic es requiring wide-area coverage can be installed at several adjacent LDACS cells . The handover between the involved LDACS cells is seamless, automatic, and tra nsparent to the user. Therefore, the LDACS communications concept enables the a eronautical communication infrastructure to support future dynamic airspace mana gement concepts. LDACS supports communications in all airspaces (airport, termina l maneuvering area, and en route) and on the airport surface. The physical LDAC S cell coverage is effectively decoupled from the operational coverage required for a particular service. This is new in aeronautical communications. Services requiring wide-area coverage can be installed at several adjacent LDACS cells. The handover between the involved LDACS cells is seamless, automatic, and trans parent to the user. Therefore, the LDACS communications concept enables the aer onautical communication infrastructure to support future dynamic airspace manage ment concepts.
</t> </t>
<section anchor='Advances'><name>Advances Beyond the State-of-the-Ar t</name> <section anchor='Advances'><name>Advances beyond the State of the Ar t</name>
<t> <t>
LDACS will offer several capabilities, not yet provided in c ontemporarily deployed aeronautical communications systems. All these were alrea dy tested and confirmed in lab or flight trials with available LDACS prototype h ardware <xref target="BEL2021"/> <xref target="MAE20211"/>. LDACS will offer several capabilities that are not yet provided in contemporaril y deployed aeronautical communications systems. These capabilities were already tested and confirmed in lab or flight trials with available LDACS prototype hard ware <xref target="BEL2021"/> <xref target="MAE20211"/>.
</t> </t>
<section anchor='Priorities'><name>Priorities</name> <section anchor='Priorities'><name>Priorities</name>
<t> <t>
LDACS is able to manage service priorities, an important feature not available in some of the current data link deployments. Thus, LDAC S guarantees bandwidth availability, low latency, and high continuity of service for safety critical ATS applications while simultaneously accommodating less sa fety-critical AOC services. LDACS is able to manage service priorities, which is an important feature that is not available in some of the current data link deploym ents. Thus, LDACS guarantees bandwidth availability, low latency, and high cont inuity of service for safety-critical ATS applications while simultaneously acco mmodating less safety-critical AOC services.
</t> </t>
</section> </section>
<section anchor='Security'><name>Security</name> <section anchor='Security'><name>Security</name>
<t> <t>
LDACS is a secure data link with built-in security mecha nisms. It enables secure data communications for ATS and AOC services, includin g secured private communications for aircraft operators and Air traffic Network Service Providers (ANSP). This includes concepts for key and trust management, m utual authentication and key establishment protocols, key derivation measures, u ser and control message-in-transit protection, secure logging and availability a nd robustness measures <xref target="MAE20182"/> <xref target="MAE2021"/>. LDACS is a secure data link with built-in security mecha nisms. It enables secure data communications for ATS and AOC services, includin g secured private communications for aircraft operators and Air Traffic Network Service Providers (ANSPs). This includes concepts for key and trust management, Mutual Authentication and Key Establishment (MAKE) protocols, key derivation mea sures, user and control message-in-transit protection, secure logging, and avail ability and robustness measures <xref target="MAE20182"/> <xref target="MAE2021" />.
</t> </t>
</section> </section>
<section anchor='highdatarates'><name>High Data Rates</name> <section anchor='highdatarates'><name>High Data Rates</name>
<t> <t>
The user data rate of LDACS is 315 kbit/s to 1428 kbit/s The user data rate of LDACS is 315 kbit/s to 1428 kbit/s
on the Forward Link (FL) for the Ground-to-Air (G2A) connection, and 294 kbit/s on the Forward Link (FL) for the Ground-to-Air (G2A) connection, and 294 kbit/s
to 1390 kbit/s on the Reverse Link (RL) for the Air-to-Ground (A2G) connection, to 1390 kbit/s on the Reverse Link (RL) for the Air-to-Ground (A2G) connection,
depending on coding and modulation. This is up to two orders of magnitude grea depending on coding and modulation.
ter than current terrestrial digital aeronautical communications systems, such a This is up to two orders of magnitude greater than what current terrestrial digi
s the VHF Data Link mode 2 (VDLm2), provide <xref target="ICAO2019"/> <xref targ tal
et="GRA2020"/>. aeronautical communications systems, such as the VHF Data Link mode 2 (VDLm2),
</t> provide; see <xref target="ICAO2019"/> <xref target="GRA2020"/>.
</t>
</section> </section>
</section> </section>
<section anchor='application'><name>Application</name> <section anchor='application'><name>Application</name>
<t> <t>
LDACS will be used by several aeronautical applications ranging from enhanced communications protocol stacks (multi-homed mobile IPv6 networks i n the aircraft and potentially ad-hoc networks between aircraft) to broadcast co mmunication applications (GNSS correction data) and integration with other servi ce domains (using the communications signal for navigation) <xref target="MAE202 11"/>. Also, a digital voice service offering better quality and service than cu rrent HF and VHF systems is foreseen. LDACS will be used by several aeronautical applications ranging from enhanced communications protocol stacks (multihomed mobile IPv6 networks in the aircraft and potentially ad-hoc networks between aircraft) to broadcast com munication applications (Global Navigation Satellite System (GNSS) correction da ta) and integration with other service domains (using the communications signal for navigation) <xref target="MAE20211"/>. Also, a digital voice service offerin g better quality and service than current HF and VHF systems is foreseen.
</t> </t>
<section anchor='MultilinkTechnology'><name>Air/Ground Multilink </name> <section anchor='MultilinkTechnology'><name>Air/Ground Multilink </name>
<t> <t>It is expected that LDACS, together with upgraded satelli
It is expected that LDACS, together with upgraded satell te-based communications systems, will be deployed within the FCI and constitute
ite-based communications systems, will be deployed within the FCI and constitute one of the main components of the multilink concept within the FCI.
one of the main components of the multilink concept within the FCI.
</t> </t>
<t> <t>
Both technologies, LDACS and satellite systems, have the ir specific benefits and technical capabilities which complement each other. Esp ecially, satellite systems are well-suited for large coverage areas with less de nse air traffic, e.g. oceanic regions. LDACS is well-suited for dense air traff ic areas, e.g., continental areas or hot-spots around airports and terminal airs pace. In addition, both technologies offer comparable data link capacity and, t hus, are well-suited for redundancy, mutual back-up, or load balancing. Both technologies, LDACS and satellite systems, have the ir specific benefits and technical capabilities that complement each other. Sate llite systems are especially well-suited for large coverage areas with less dens e air traffic, e.g., oceanic regions. LDACS is well-suited for dense air traffi c areas, e.g., continental areas or hotspots around airports and terminal airspa ce. In addition, both technologies offer comparable data link capacity; thus, b oth are well-suited for redundancy, mutual back-up, or load balancing.
</t> </t>
<t> <t>
Technically the FCI multilink concept will be realized b y multi-homed mobile IPv6 networks in the aircraft. The related protocol stack is currently under development by ICAO, within SESAR, and the IETF. Currently tw o layers of mobility are foreseen. Local mobility within the LDACS access networ k is realized through PMIPv6, global mobility between “multi-link” access networ ks (which need not be LDACS) is implemented on top of LISP <xref target="I-D.hai ndl-lisp-gb-atn" format="default"/> <xref target="I-D.ietf-lisp-rfc6830bis" form at="default"/> <xref target="I-D.ietf-lisp-rfc6833bis" format="default"/>. Technically, the FCI multilink concept will be realized by multihomed mobile IPv6 networks in the aircraft. The related protocol stack is currently under development by ICAO, within SESAR, and the IETF. Currently, t wo layers of mobility are foreseen. Local mobility within the LDACS access netwo rk is realized through Proxy Mobile IPv6 (PMIPv6), and global mobility between " multilink" access networks (which need not be LDACS) is implemented on top of LI SP <xref target="I-D.haindl-lisp-gb-atn" format="default"/> <xref target="RFC930 0" format="default"/> <xref target="RFC9301" format="default"/>.
</t> </t>
</section> </section>
<section anchor='A2A'><name>Air/Air Extension for LDACS</name> <section anchor='A2A'><name>Air/Air Extension for LDACS</name>
<t> <t>
A potential extension of the multilink concept is its ex tension to the integration of ad-hoc networks between aircraft. A potential extension of the multilink concept is its ex tension to the integration of ad-hoc networks between aircraft.
</t> </t>
<t> <t>
Direct A/A communication between aircraft in terms of ad -hoc data networks are currently considered a research topic since there is no i mmediate operational need for it, although several possible use cases are discus sed (Automatic Dependent Surveillance - Broadcast (ADS-B), digital voice, wake v ortex warnings, and trajectory negotiation) <xref target="BEL2019"/>. It should also be noted, that currently deployed analog VHF voice radios support direct v oice communication between aircraft, making a similar use case for digital voice plausible. Direct A/A communication between aircraft in terms of ad -hoc data networks is currently considered a research topic since there is no im mediate operational need for it, although several possible use cases are discuss ed (Automatic Dependent Surveillance - Broadcast (ADS-B), digital voice, wake vo rtex warnings, and trajectory negotiation) <xref target="BEL2019"/>. It should also be noted that currently deployed analog VHF voice radios support direct voi ce communication between aircraft, making a similar use case for digital voice p lausible.
</t> </t>
<t> <t>
LDACS A/A is currently not part of the standardization p rocess and will not be covered within this document. However, it is planned that LDACS A/A will be rolled out after the initial deployment of LDACS A/G, then be ing seamlessly integrated in the existing LDACS ground-based system. LDACS A/A is currently not a part of the standardization process and will not be covered within this document. However, it is planned th at LDACS A/A will be rolled out after the initial deployment of LDACS A/G and se amlessly integrated in the existing LDACS ground-based system.
</t> </t>
</section> </section>
<section anchor='FlightGuidance'><name>Flight Guidance</name> <section anchor='FlightGuidance'><name>Flight Guidance</name>
<t> <t>
The FCI (and therefore LDACS) is used to provide flight guidance. This is realized using three applications: The FCI (and therefore LDACS) is used to provide flight guidance. This is realized using three applications:
</t><dl spacing='compact'> </t><ol spacing='compact'>
<dt>1.</dt><dd> <li>Context Management (CM): The CM application manages
Context Management (CM): The CM application manages the automatic logical connection to the ATC center currently responsible to guid
the automatic logical connection to the ATC center currently responsible to guid e the aircraft. Currently, this is done by the air crew manually changing VHF v
e the aircraft. Currently, this is done by the air crew manually changing VHF v oice frequencies according to the progress of the flight. The CM application au
oice frequencies manually according to the progress of the flight. The CM appli tomatically sets up equivalent sessions.
cation automatically sets up equivalent sessions. </li>
</dd> <li>Controller-Pilot Data Link Communications (CPDLC): T
<dt>2.</dt><dd> he CPDLC application provides the air crew with the ability to exchange data mes
Controller Pilot Data Link Communications (CPDLC): T sages similar to text messages with the currently responsible ATC center. The C
he CPDLC application provides the air crew with the ability to exchange data mes PDLC application takes over most of the communication currently performed over V
sages similar to text messages with the currently responsible ATC center. The C HF voice and enables new services that do not lend themselves to voice communica
PDLC application takes over most of the communication currently performed over V tion (i.e., trajectory negotiation).
HF voice and enables new services that do not lend themselves to voice communica </li>
tion (i.e., trajectory negotiation). <li>Automatic Dependent Surveillance - Contract (ADS-C):
</dd> ADS-C reports the position of the aircraft to the currently active ATC center.
<dt>3.</dt><dd> Reporting is bound to "contracts", i.e., pre-defined events related to the prog
Automatic Dependent Surveillance - Contract (ADS-C): ress of the flight (i.e., the trajectory). ADS-C and CPDLC are the primary appl
ADS-C reports the position of the aircraft to the currently active ATC center. ications used for implementing in-flight trajectory management.
Reporting is bound to "contracts", i.e., pre-defined events related to the prog </li>
ress of the flight (i.e., the trajectory). ADS-C and CPDLC are the primary appl </ol>
ications used for implementing in-flight trajectory management.
</dd>
</dl>
<t> <t>
CM, CPDLC, and ADS-C are available on legacy datalinks, but are not widely deployed and with limited functionality. CM, CPDLC, and ADS-C are available on legacy data links but are not widely deployed and with limited functionality.
</t> </t>
<t> <t>
Further ATC applications may be ported to use the FCI or LDACS as well. A notable application is GBAS for secure, automated landings: Th e Global Navigation Satellite System (GNSS) based GBAS is used to improve the ac curacy of GNSS to allow GNSS based instrument landings. This is realized by send ing GNSS correction data (e.g., compensating ionospheric errors in the GNSS sign al) to the aircraft's GNSS receiver via a separate data link. Currently, the VDB data link is used. VDB is a narrowband single-purpose datalink without advance d security only used to transmit GBAS correction data. This makes VDB a natural candidate for replacement by LDACS <xref target="MAE20211"/>. Further ATC applications may be ported to use the FCI or LDACS as well. A notable application is the Ground-Based Augmentation System (G BAS) for secure, automated landings. The GNSS-based GBAS is used to improve the accuracy of GNSS to allow GNSS-based instrument landings. This is realized by se nding GNSS correction data (e.g., compensating ionospheric errors in the GNSS si gnal) to the aircraft's GNSS receiver via a separate data link. Currently, the V HF Data Broadcast (VDB) data link is used. VDB is a narrowband one-way, single-p urpose data link without advanced security and is only used to transmit GBAS cor rection data. These shortcomings show a clear need to replace VDB. A natural ca ndidate to replace it is LDACS, because it is a bidirectional data link, also op erates in non-line-of sight scenarios, offers strong integrated link-layer secur ity, and has a considerably larger operational range than VDB <xref target="MAE2 0211"/>.
</t> </t>
</section> </section>
<section anchor='BusinessCommunicationofAirlines'><name>Busines s Communications of Airlines</name> <section anchor='BusinessCommunicationofAirlines'><name>Busines s Communications of Airlines</name>
<t> <t>
In addition to air traffic services, AOC services are tr ansmitted over LDACS. AOC is a generic term referring to the business communica tion of airlines, between the airlines and service partners on the ground and th eir own aircraft in the air. Regulatory-wise, this is considered related to saf ety and regularity of flight and may therefore, be transmitted over LDACS. AOC communication is considered the main business case for LDACS communications serv ice providers since modern aircraft generate significant amounts of data (e.g., engine maintenance data). In addition to ATSs, AOC services are transmitted over L DACS. AOC is a generic term referring to the business communication of airlines between the airlines and service partners on the ground and their own aircraft in the air. Regulatory-wise, this is considered related to safety and regularit y of flight; therefore, it may be transmitted over LDACS. AOC communication is considered the main business case for LDACS communications service providers sin ce modern aircraft generate significant amounts of data (e.g., engine maintenanc e data).
</t> </t>
</section> </section>
<section anchor='LDACSNavigation'><name>LDACS-based Navigation</ name> <section anchor='LDACSNavigation'><name>LDACS-Based Navigation</ name>
<t> <t>
Beyond communications, radio signals can always also be used for navigation. This fact is used for the LDACS navigation concept. Beyond communications, radio signals can always be used for navigation as well. This fact is used for the LDACS navigation concept.
</t> </t>
<t> <t>
For future aeronautical navigation, ICAO recommends the further development of GNSS based technologies as primary means for navigation. Due to the large separation between navigational satellites and aircraft, the p ower of the GNSS signals received by the aircraft is, however, very low. As a r esult, GNSS disruptions might occasionally occur due to unintentional interferen ce, or intentional jamming. Yet the navigation services must be available with sufficient performance for all phases of flight. Therefore, during GNSS outages , or blockages, an alternative solution is needed. This is commonly referred to as Alternative Positioning, Navigation, and Timing (APNT). For future aeronautical navigation, ICAO recommends the further development of GNSS-based technologies as primary means for navigation. However, due to the large separation between navigational satellites and aircra ft, the power of the GNSS signals received by the aircraft is very low. As a re sult, GNSS disruptions might occasionally occur due to unintentional interferenc e or intentional jamming. Yet, the navigation services must be available with s ufficient performance for all phases of flight. Therefore, during GNSS outages or blockages, an alternative solution is needed. This is commonly referred to a s Alternative Positioning, Navigation, and Timing (APNT).
</t> </t>
<t> <t>
One such APNT solution is based on exploiting the built- One such APNT solution is based on exploiting the built-
in navigation capabilities of LDACS operation. That is, the normal operation of in navigation capabilities of LDACS operation. That is, the normal operation of
LDACS for ATC and AOC communications would also directly enable the aircraft to LDACS for ATC and AOC communications would also directly enable the aircraft to
navigate and obtain a reliable timing reference from the LDACS GSs. Current cel navigate and obtain a reliable timing reference from the LDACS GSs. Current cel
l planning for Europe shows 84 LDACS cells to be sufficient <xref target="MOST20 l planning for Europe shows 84 LDACS cells to be sufficient <xref target="MOST20
18"/> to cover the continent at sufficient service level. If more than three Gro 18"/> to cover the continent at a sufficient service level.
und Stations (GS) are visible by the aircraft, via knowing the exact positions o
f these and having a good channel estimation (which LDACS does due to numerous w If more than three GSs are visible by the aircraft, via knowing the exact positi
orks mapping the L-band channel characteristics <xref target="SCHN2018"/> ) it i ons of these and having a good channel estimation (which LDACS does due to numer
s possible to calculate the position of the aircraft via measuring signal propag ous works mapping the L-band channel characteristics <xref target="SCHN2018"/>),
ation times to each GS. In flight trials in 2019 with one aircraft (and airborne it is possible to calculate the position of the aircraft via measuring signal p
radio inside it) and just four GS, navigation feasibility was demonstrated with ropagation times to each GS.
in the footprint of all four GS with a 95th percentile position-domain error of In flight trials in 2019 with one aircraft (and airborne radio inside it) and
171.1m <xref target="OSE2019"/> <xref target="BEL2021"/> <xref target="MAE20211" just four GSs, navigation feasibility was demonstrated within the footprint of
/>. As such, LDACS can be used independently of GNSS as a navigation alternative all four GSs with a 95th percentile position-domain error of 171.1m <xref
. Positioning errors will decrease markedly as more GSes are deployed. <xref ta target="OSE2019"/> <xref target="BEL2021"/> <xref target="MAE20211"/>. As
rget="OSE2019"/> <xref target="BEL2021"/> <xref target="MAE20211"/> such, LDACS can be used independently of GNSS as a navigation alternative.
Positioning errors will decrease markedly as more GSs are deployed <xref
target="OSE2019"/> <xref target="BEL2021"/> <xref target="MAE20211"/>.
</t> </t>
<t> <t>
LDACS navigation has already been demonstrated in practi ce in two flight measurement campaigns <xref target="SHU2013"/> <xref target="BE L2021"/> <xref target="MAE20211"/>. LDACS navigation has already been demonstrated in practi ce in two flight measurement campaigns <xref target="SHU2013"/> <xref target="BE L2021"/> <xref target="MAE20211"/>.
</t> </t>
</section> </section>
</section> </section>
</section> </section>
<section anchor='RequirementstoLDACS'><name>Requirements</name> <section anchor='RequirementstoLDACS'><name>Requirements</name>
<t> <t>
The requirements for LDACS are mostly defined by its application are a: Communications related to safety and regularity of flight. The requirements for LDACS are mostly defined by its application are a: communications related to safety and regularity of flight.
</t> </t>
<t> <t>
A particularity of the current aeronautical communication landscape A particularity of the current aeronautical communication landscape
is that it is heavily regulated. Aeronautical data links (for applications relat is that it is heavily regulated.
ed to safety and regularity of flight) may only use spectrum licensed to aviatio Aeronautical data links (for applications related to safety and regularity of
n and data links endorsed by ICAO. Nation states can change this locally; howeve flight) may only use spectrum licensed to aviation and data links endorsed by
r, due to the global scale of the air transportation system, adherence to these ICAO. Nation states can change this locally; however, due to the global scale
practices is to be expected. of the air transportation system, adherence to these practices is to be
expected.
</t> </t>
<t> <t>
Aeronautical data links for the ATN are therefore expected to remain in service for decades. The VDLm2 data link currently used for digital terrest rial internetworking was developed in the 1990s (the use of the Open Systems Int erconnection (OSI) stack indicates that as well). VDLm2 is expected to be used at least for several decades to come. In this respect aeronautical communication s (for applications related to safety and regularity of flight) is more comparab le to industrial applications than to the open Internet. Aeronautical data links for the ATN are therefore expected to remain in service for decades. The VDLm2 data link currently used for digital terrest rial internetworking was developed in the 1990s (the use of the Open Systems Int erconnection (OSI) stack indicates that as well). VDLm2 is expected to be used at least for several decades to come. In this respect, aeronautical communicatio ns for applications related to safety and regularity of flight is more comparabl e to industrial applications than to the open Internet.
</t> </t>
<t> <t>
Internetwork technology is already installed in current aircraft. Cu rrent ATS applications use either Aircraft Communications Addressing and Reporti ng System (ACARS) or the OSI stack. The objective of the development effort of LDACS, as part of the FCI, is to replace legacy OSI stack and proprietary ACARS internetwork technologies with industry standard IP technology. It is anticipat ed that the use of Commercial Off-The-Shelf (COTS) IP technology mostly applies to the ground network. The avionics networks on the aircraft will likely be hea vily modified versions of Ethernet or proprietary. Internetwork technology is already installed in current aircraft. Cu rrent ATS applications use either the Aircraft Communications Addressing and Rep orting System (ACARS) or the OSI stack. The objective of the development effort of LDACS, as part of the FCI, is to replace legacy OSI stack and proprietary AC ARS internetwork technologies with industry standard IP technology. It is antic ipated that the use of Commercial Off-The-Shelf (COTS) IP technology mostly appl ies to the ground network. The avionics networks on the aircraft will likely be heavily modified versions of Ethernet or proprietary.
</t> </t>
<t> <t>
AOC applications currently mostly use the same stack (although some Currently, AOC applications mostly use the same stack (although some
applications, like the graphical weather service may use the commercial passenge applications, like the graphical weather service, may use the commercial passen
r network). This creates capacity problems (resulting in excessive amounts of t ger network).
imeouts) since the underlying terrestrial data links do not provide sufficient b This creates capacity problems (resulting in excessive amounts of timeouts) sinc
andwidth (i.e., with VDLm2 currently in the order of 10 kbit/s). The use of non- e the underlying terrestrial data links do not provide sufficient bandwidth (i.e
aviation specific data links is considered a security problem. Ideally the aero ., with VDLm2 currently in the order of 10 kbit/s). The use of non-aviation-spec
nautical IP internetwork, hence the ATN over which only communications related t ific data links is considered a security problem. Ideally, the aeronautical IP i
o safety and regularity of flight is handled, and the Internet should be complet nternetwork (hence the ATN over which only communications related to safety and
ely separated at Layer 3. regularity of flight is handled) and the Internet should be completely separated
at Layer 3.
</t> </t>
<t> <t>
The objective of LDACS is to provide a next generation terrestrial d ata link designed to support IP addressing and provide much higher bandwidth to avoid the currently experienced operational problems. The objective of LDACS is to provide a next-generation terrestrial d ata link designed to support IP addressing and provide much higher bandwidth to avoid the operational problems that are currently experienced.
</t> </t>
<t> <t>
The requirement for LDACS is therefore to provide a terrestrial high -throughput data link for IP internetworking in the aircraft. The requirement for LDACS is therefore to provide a terrestrial high -throughput data link for IP internetworking in the aircraft.
</t> </t>
<t> <t>
In order to fulfil the above requirement LDACS needs to be interoper able with IP (and IP-based services like Voice-over-IP) at the gateway connectin g the LDACS network to other aeronautical ground networks (i.e., the ATN). On t he avionics side, in the aircraft, aviation specific solutions are to be expecte d. In order to fulfill the above requirement, LDACS needs to be interop erable with IP (and IP-based services like Voice-over-IP) at the gateway connect ing the LDACS network to other aeronautical ground networks (i.e., the ATN). On the avionics side, in the aircraft, aviation-specific solutions are to be expec ted.
</t> </t>
<t> <t>
In addition to these functional requirements, LDACS and its IP stack need to fulfil the requirements defined in RTCA DO-350A/EUROCAE ED-228A <xref t arget="DO350A"/>. This document defines continuity, availability, and integrity requirements at different scopes for each air traffic management application (CP DLC, CM, and ADS-C). The scope most relevant to IP over LDACS is the Communicati ons Service Provider (CSP) scope. In addition to these functional requirements, LDACS and its IP stack need to fulfill the requirements defined in RTCA DO-350A/EUROCAE ED-228A <xref target="DO350A"/>. This document defines continuity, availability, and integrity requirements at different scopes for each ATM application (CPDLC, CM, and ADS-C ). The scope most relevant to IP over LDACS is the Communications Service Provid er (CSP) scope.
</t> </t>
<t> <t>
Continuity, availability, and integrity requirements are defined in <xref target="DO350A"/> volume 1 Table 5-14, and Table 6-13. <xref target="appen dix"/> presents the required information. Continuity, availability, and integrity requirements are defined in Volume 1 of <xref target="DO350A"/> in Tables 5-14 and 6-13. <xref target="appen dix"/> presents the required information.
</t> </t>
<t> <t>
In a similar vein, requirements to fault management are defined in t he same tables. In a similar vein, requirements to fault management are defined in t he same tables.
</t> </t>
</section> </section>
<section anchor='Characteristics'><name>Characteristics</name> <section anchor='Characteristics'><name>Characteristics</name>
<t> <t>
LDACS will become one of several wireless access networks connecting aircraft to the ATN implemented by the FCI. LDACS will become one of several wireless access networks connecting aircraft to the ATN implemented by the FCI.
</t> </t>
<t> <t>
The current LDACS design is focused on the specification of layer on e and two. However, for the purpose of this work, only layer two details are dis cussed here. The current LDACS design is focused on the specification of Layers 1 and 2. However, for the purpose of this work, only Layer 2 details are discusse d here.
</t> </t>
<t> <t>
Achieving the stringent continuity, availability, and integrity requ irements defined in <xref target="DO350A"/> will require the specification of la yer 3 and above mechanisms (e.g., reliable crossover at the IP layer). Fault ma nagement mechanisms are similarly unspecified as of November 2022. Current regu latory documents do not fully specify the above mechanism yet. However, a short overview of the current state shall be given throughout each section here. Achieving the stringent continuity, availability, and integrity requ irements defined in <xref target="DO350A"/> will require the specification of La yer 3 and above mechanisms (e.g., reliable crossover at the IP layer). Fault ma nagement mechanisms are similarly unspecified as of November 2022. Current regu latory documents do not fully specify the above mechanism yet. However, a short overview of the current state shall be given throughout each section here.
</t> </t>
<section anchor='LDACSSub-Network'><name>LDACS Access Network</name> <section anchor='LDACSSub-Network'><name>LDACS Access Network</name>
<t> <t>
An LDACS access network contains an Access Router (AC-R) and sev eral GS, each of them providing one LDACS radio cell. An LDACS access network contains an Access Router (AC-R) and sev eral GSs, each of them providing one LDACS radio cell.
</t> </t>
<t> <t>
User plane interconnection to the ATN is facilitated by the AC-R peering with an A/G Router connected to the ATN. User-plane interconnection to the ATN is facilitated by the AC-R peering with an A/G Router connected to the ATN.
</t> </t>
<t> <t>
The internal control plane of an LDACS access network interconne cts the GSs. An LDACS access network is illustrated in The internal control plane of an LDACS access network interconne cts the GSs. An LDACS access network is illustrated in
<xref target="fig_LDACSwirelesstopology"/>. <xref target="fig_LDACSwirelesstopology"/>. Dashes denote the user plane and po ints denote the control plane.
</t> </t>
<figure title="LDACS access network with three GSs and one AS. <figure title="LDACS Access Network with Three GSs and One AS" anchor="fig_LDACS
dashes denotes the user plane and points the control wirelesstopology">
plane" anchor="fig_LDACSwirelesstopology"> <artwork><![CDATA[
<artwork>
<![CDATA[
wireless user wireless user
link plane link plane
AS-------------GS---------------AC-R---A/G-----ATN AS-------------GS---------------AC-R---A/G-----ATN
.............. | Router .............. | Router
control . | control . |
plane . | plane . |
. | . |
GS----------------| GS----------------|
. | . |
. | . |
GS----------------+ GS----------------+]]></artwork>
]]>
</artwork>
</figure> </figure>
</section> </section>
<section anchor='topology'><name>Topology</name> <section anchor='topology'><name>Topology</name>
<t> <t>
LDACS is a cellular point-to-multipoint system. It assumes a sta r-topology in each cell where Aircraft Stations (AS) belonging to aircraft withi n a certain volume of space (the LDACS cell) are connected to the controlling GS . The LDACS GS is a centralized instance that controls LDACS A/G communications within its cell. The LDACS GS can simultaneously support multiple bidirectiona l communications to the ASs under its control. LDACS's GSs themselves are conne cted to each other and the AC-R. LDACS is a cellular point-to-multipoint system. It assumes a sta r topology in each cell where Aircraft Stations (ASs) belonging to aircraft with in a certain volume of space (the LDACS cell) are connected to the controlling G S. The LDACS GS is a centralized instance that controls LDACS A/G communication s within its cell. The LDACS GS can simultaneously support multiple bidirection al communications to the ASs under its control. LDACS's GSs themselves are conn ected to each other and the AC-R.
</t> </t>
<t> <t>
Prior to utilizing the system an aircraft has to register with t he controlling GS to establish dedicated logical channels for user and control d ata. Control channels have statically allocated resources, while user channels have dynamically assigned resources according to the current demand. Logical ch annels exist only between the GS and the AS. Prior to utilizing the system, an aircraft has to register with the controlling GS to establish dedicated logical channels for user and control data. Control channels have statically allocated resources while user channels have dynamically assigned resources according to the current demand. Logical ch annels exist only between the GS and the AS.
</t> </t>
</section> </section>
<section anchor='LDACSPhysicalLayer'><name>LDACS Protocol Stack</name> <section anchor='LDACSPhysicalLayer'><name>LDACS Protocol Stack</name>
<t> The protocol stack of LDACS is implemented in the AS and GS: It <t> The protocol stack of LDACS is implemented in the AS and GS. It
consists of the Physical Layer (PHY) with five major, functional blocks above it consists of the PHY with five major functional blocks above it.
. Four are placed in the Data Link Layer (DLL) of the AS and GS: (1) Medium Acc Four are placed in the DLL of the AS and GS: Medium Access Control (MAC) layer,
ess Control (MAC) Layer, (2) Voice Interface (VI), (3) Data Link Service (DLS), Voice Interface (VI), Data Link Service (DLS), and LDACS Management Entity (LME)
and (4) LDACS Management Entity (LME). The fifth entity resides within the sub- . The fifth entity, the SNP, resides within the subnetwork layer. The LDACS rad
network layer: (5) the Sub-Network Protocol (SNP). The LDACS radio is externall io is externally connected to a voice unit and radio control unit via the AC-R t
y connected to a voice unit, radio control unit, and via the AC-R to the ATN net o the ATN network.
work.
</t> </t>
<t>LDACS is considered an ATN/IPS radio access technology, from the view of ICAO's regulatory framework. Hence, the interface between ATN and LDACS must be IPv6 based, as regulatory documents, such as ICAO Doc 9896 <xref target ="ICAO2015"/> and DO-379 <xref target="RTCA2019"/> clearly foresee that. The tr anslation between IPv6 layer and SNP layer is currently the subject of ongoing s tandardization efforts and at the time of writing not finished yet. <t>LDACS is considered an ATN/IPS radio access technology from the v iew of ICAO's regulatory framework. Hence, the interface between ATN and LDACS must be IPv6-based, as regulatory documents such as ICAO Doc 9896 <xref target=" ICAO2015"/> and DO-379 <xref target="RTCA2019"/> clearly foresee that. The tran slation between the IPv6 layer and SNP layer is currently the subject of ongoing standardization efforts and not finished yet at the time of writing.
</t> </t>
<t> <t>
<xref target="fig_LDACSprotocolstack"/> shows the protocol stack of LDACS as implemented in the AS and GS. Acronyms used here are introduced thr oughout the upcoming sections. <xref target="fig_LDACSprotocolstack"/> shows the protocol stack of LDACS as implemented in the AS and GS. Acronyms used here are introduced thr oughout the upcoming sections.
</t> </t>
<figure title="LDACS protocol stack in AS and GS" anchor="fig_L <figure title="LDACS Protocol Stack in the AS and GS" anchor="f
DACSprotocolstack"> ig_LDACSprotocolstack">
<artwork> <artwork><![CDATA[
<![CDATA[
IPv6 Network Layer IPv6 Network Layer
| |
Airborne Voice | Airborne Voice |
Interface (AVI)/ | Radio Control Unit (RCU) Interface (AVI) / | Radio Control Unit (RCU)
Voice Unit (VU) | Voice Unit (VU) |
| | | |
| +------------------+ +----+ | +------------------+ +----+
| | SNP |--| | Sub-Network | | SNP |--| | Subnetwork
| | | | | Layer | | | | | Layer
| +------------------+ | | | +------------------+ | |
| | | LME| | | | LME|
+-----+ +------------------+ | | +-----+ +------------------+ | |
| VI | | DLS | | | LLC Layer | VI | | DLS | | | LLC Layer
+-----+ +------------------+ +----+ +-----+ +------------------+ +----+
| | | | | |
DCH DCH DCCH/CCCH DCH DCH DCCH/CCCH
| RACH/BCCH | RACH/BCCH
| | | |
skipping to change at line 656 skipping to change at line 663
| | Layer | | Layer
+-------------------------------------+ +-------------------------------------+
| |
+-------------------------------------+ +-------------------------------------+
| PHY | Physical Layer | PHY | Physical Layer
+-------------------------------------+ +-------------------------------------+
| |
| |
((*)) ((*))
FL/RL radio channels FL/RL radio channels
separated by FDD separated by FDD]]></artwork>
]]>
</artwork>
</figure> </figure>
<section anchor='LDACSDphyLayer'><name>LDACS Physical Layer</name> <section anchor='LDACSDphyLayer'><name>LDACS Physical Layer</name>
<t> <t>
The physical layer provides the means to transfer data over The physical layer provides the means to transfer data over
the radio channel. The LDACS GS supports bidirectional links to multiple aircra the radio channel. The LDACS GS supports bidirectional links to multiple aircra
ft under its control. The FL direction at the G2A connection and the RL directi ft under its control.
on at the A2G connection are separated by Frequency Division Duplex (FDD). FL a
nd RL use a 500 kHz channel each. The GS transmits a continuous stream of Ortho The FL direction at the G2A connection and the RL direction at the A2G connectio
gonal Frequency-Division Multiplexing Access (OFDM) symbols on the FL. In the R n are separated by Frequency Division Duplex (FDD). FL and RL use a 500 kHz cha
L different aircraft are separated in time and frequency using Orthogonal Freque nnel each. The GS transmits a continuous stream of Orthogonal Frequency Divisio
ncy-Division Multiple Access (OFDMA). Aircraft thus transmit discontinuously on n Multiplexing Access (OFDM) symbols on the FL. In the RL, different aircraft a
the RL via short radio bursts sent in precisely defined transmission opportuniti re separated in time and frequency using Orthogonal Frequency Division Multiple
es allocated by the GS. Access (OFDMA). Thus, aircraft transmit discontinuously on the RL via short radi
o bursts sent in precisely defined transmission opportunities allocated by the G
S.
</t> </t>
</section> </section>
<section anchor='LDACSDataLinkLayer'><name>LDACS Data Link Layer</na me> <section anchor='LDACSDataLinkLayer'><name>LDACS Data Link Layer</na me>
<t> <t>
The data-link layer provides the necessary protocols to faci litate concurrent and reliable data transfer for multiple users. The LDACS data link layer is organized in two sub-layers: The medium access sub-layer and the Logical Link Control (LLC) sub-layer. The medium access sub-layer manages the o rganization of transmission opportunities in slots of time and frequency. The L LC sub-layer provides acknowledged point-to-point logical channels between the a ircraft and the GS using an Automatic Repeat reQuest (ARQ) protocol. LDACS also supports unacknowledged point-to-point channels and G2A Broadcast transmission. The data link layer provides the necessary protocols to faci litate concurrent and reliable data transfer for multiple users. The LDACS data link layer is organized in two sub-layers: the medium access sub-layer and the Logical Link Control (LLC) sub-layer. The medium access sub-layer manages the o rganization of transmission opportunities in slots of time and frequency. The L LC sub-layer provides acknowledged point-to-point logical channels between the a ircraft and the GS using an Automatic Repeat reQuest (ARQ) protocol. LDACS also supports unacknowledged point-to-point channels and G2A broadcast transmission.
</t> </t>
<section anchor='MACservice'><name>Medium Access Control (MAC) S ervices</name> <section anchor='MACservice'><name>Medium Access Control (MAC) S ervices</name>
<t> <t>
The MAC time framing service provides the frame structur e necessary to realize slot-based time-division multiplex-access on the physical link. It provides the functions for the synchronization of the MAC framing str ucture and the PHY Layer framing. The MAC time framing provides a dedicated tim e slot for each logical channel. The MAC time framing service provides the frame structur e necessary to realize slot-based time-division multiplex-access on the physical link. It provides the functions for the synchronization of the MAC framing str ucture and the PHY layer framing. The MAC time framing provides a dedicated tim e slot for each logical channel.
</t> </t>
<t> <t>
The MAC sub-layer offers access to the physical channel to its service users. Channel access is provided through transparent logical ch annels. The MAC sub-layer maps logical channels onto the appropriate slots and manages the access to these channels. Logical channels are used as interface be tween the MAC and LLC sub-layers. The MAC sub-layer offers access to the physical channel to its service users. Channel access is provided through transparent logical ch annels. The MAC sub-layer maps logical channels onto the appropriate slots and manages the access to these channels. Logical channels are used as interface be tween the MAC and LLC sub-layers.
</t> </t>
</section> </section>
<section anchor='DLservice'><name>Data Link Service (DLS) Servic es</name> <section anchor='DLservice'><name>Data Link Services (DLSs)</nam e>
<t> <t>
The DLS provides acknowledged and unacknowledged (includ ing broadcast and packet mode voice) bidirectional exchange of user data. If us er data is transmitted using the acknowledged DLS, the sending DLS entity will w ait for an acknowledgement from the receiver. If no acknowledgement is received within a specified time frame, the sender may automatically try to retransmit i ts data. However, after a certain number of failed retries, the sender will sus pend further retransmission attempts and inform its client of the failure. The DLS provides acknowledged and unacknowledged (includ ing broadcast and packet mode voice) bidirectional exchange of user data. If us er data is transmitted using the acknowledged DLS, the sending DLS entity will w ait for an acknowledgement from the receiver. If no acknowledgement is received within a specified time frame, the sender may automatically try to retransmit i ts data. However, after a certain number of failed retries, the sender will sus pend further retransmission attempts and inform its client of the failure.
</t> </t>
<t> <t>
The DLS uses the logical channels provided by the MAC: The DLS uses the logical channels provided by the MAC:
</t><dl spacing='compact'> </t><ol spacing='compact'>
<dt>1.</dt><dd> <li>A GS announces its existence and access parameters i
A GS announces its existence and access parameters i n the Broadcast Channel (BCCH).
n the Broadcast Channel (BCCH). </li>
</dd> <li>The Random-Access Channel (RACH) enables the AS to r
<dt>2.</dt><dd> equest access to an LDACS cell.
The Random-Access Channel (RACH) enables AS to reque </li>
st access to an LDACS cell. <li>In the FL, the Common Control Channel (CCCH) is used
</dd> by the GS to grant access to Data Channel (DCH) resources.
<dt>3.</dt><dd> </li>
In the FL the Common Control Channel (CCCH) is used <li>The reverse direction is covered by the RL, where AS
by the GS to grant access to data channel resources. s need to request resources before sending. This happens via the Dedicated Cont
</dd> rol Channel (DCCH).
<dt>4.</dt><dd> </li>
The reverse direction is covered by the RL, where AS <li>User data itself is communicated in the DCH on the
s need to request resources before sending. This happens via the Dedicated Cont FL and RL.
rol Channel (DCCH). </li>
</dd> </ol>
<dt>5.</dt><dd>
User data itself is communicated in the Data Channel
(DCH) on the FL and RL.
</dd>
</dl>
<t> <t>
Access to the FL and RL data channel is granted by t he scheduling mechanism implemented in the LME discussed below. Access to the FL and RL DCH is granted by the schedu ling mechanism implemented in the LME discussed below.
</t> </t>
</section> </section>
<section anchor='VIservice'><name>Voice Interface (VI) Services< /name> <section anchor='VIservice'><name>Voice Interface (VI) Services< /name>
<t> <t>
The VI provides support for virtual voice circuits. Voi The VI provides support for virtual voice circuits. Voi
ce circuits may either be set-up permanently by the GS (e.g., to emulate voice p ce circuits may be either set up permanently by the GS (e.g., to emulate voice p
arty line) or may be created on demand. arty line) or created on demand.
</t> </t>
</section> </section>
<section anchor='LMEservice'><name>LDACS Management Entity (LME) Services</name> <section anchor='LMEservice'><name>LDACS Management Entity (LME) Services</name>
<t> <t>
The mobility management service in the LME provides supp ort for registration and de-registration (cell entry and cell exit), scanning RF channels of neighboring cells and handover between cells. In addition, it mana ges the addressing of aircraft within cells. The mobility management service in the LME provides supp ort for registration and de-registration (cell entry and cell exit), scanning RF channels of neighboring cells, and handover between cells. In addition, it man ages the addressing of aircraft within cells.
</t> </t>
<t> <t>
The resource management service provides link maintenanc e (power, frequency and time adjustments), support for adaptive coding and modul ation, and resource allocation. The resource management service provides link maintenanc e (power, frequency, and time adjustments), support for adaptive coding and modu lation, and resource allocation.
</t> </t>
<t> <t>
The resource management service accepts resource request s from/for different AS and issues resource allocations accordingly. While the scheduling algorithm is not specified and a point of possible vendor differentia tion, it is subject to the following requirements: The resource management service accepts resource request s from/for different ASs and issues resource allocations accordingly. While the scheduling algorithm is not specified and a point of possible vendor differenti ation, it is subject to the following requirements:
</t><dl spacing='compact'> </t><ol spacing='compact'>
<dt>1.</dt><dd> <li>Resource scheduling must provide channel access
Resource scheduling must provide channel access acco according to the priority of the request.
rding to the priority of the request </li>
</dd> <li>Resource scheduling must support "one-time" requests
<dt>2.</dt><dd> .</li>
Resource scheduling must support "one-time" requests <li>Resource scheduling must support "permanent" request
. s that reserve a resource until the request is canceled (e.g., for digital voice
</dd> circuits).
<dt>3.</dt><dd> </li>
Resource scheduling must support "permanent" request </ol>
s that reserve a resource until the request is canceled e.g. for digital voice c
ircuits.
</dd>
</dl>
</section> </section>
</section> </section>
<section anchor='SNPservice'><name>LDACS Sub-Network Layer and Proto col Services</name> <section anchor='SNPservice'><name>LDACS Subnetwork Layer and Protoc ol Services</name>
<t> <t>
Lastly, the SNP layer of LDACS directly interacts with IPv6 Lastly, the SNP layer of LDACS directly interacts with IPv6
traffic. Incoming ATN/IPS IPv6 packets are forwarded over LDACS from and to the traffic. Incoming ATN/IPS IPv6 packets are forwarded over LDACS from and to the
aircraft. The final IP addressing structure in an LDACS subnet still needs to be aircraft.
defined; however, the current layout is considered to consist of the five netwo The final IP addressing structure in an LDACS subnet still needs to be defined;
rk segments: Air Core Net, Air Management Net, Ground Core Net, Ground Managemen however, the current layout consists of the five network segments: Air Core Net,
t Net, Ground Net. Any protocols that the ATN/IPS <xref target="ICAO2015"/> defi Air Management Net, Ground Core Net, Ground Management Net, and Ground Net. Any
nes as mandatory will reach the aircraft, however listing these here is out of s protocols that the ATN/IPS <xref target="ICAO2015"/> defines as mandatory will
cope. For more information on the technicalities of the above ATN/IPS layer, ple reach the aircraft; however, listing these here is out of scope. For more inform
ase refer to <xref target="ICAO2015"/> <xref target="RTCA2019"/> <xref target="A ation on the technicalities of the above ATN/IPS layer, please refer to <xref ta
RI2021"/>. rget="ICAO2015"/>, <xref target="RTCA2019"/>, and <xref target="ARI2021"/>.
</t> </t>
<t> <t>
The DLS provides functions required for the transfer of user plane data and control plane data over the LDACS access network. The security s ervice provides functions for secure user data communication over the LDACS acce ss network. Note that the SNP security service applies cryptographic measures a s configured by the GS. The DLS provides functions that are required for the transfe r of user-plane data and control plane data over the LDACS access network. The s ecurity service provides functions for secure user data communication over the L DACS access network. Note that the SNP security service applies cryptographic m easures as configured by the GS.
</t> </t>
</section> </section>
</section> </section>
<section anchor='LDACSMobility'><name>LDACS Mobility</name> <section anchor='LDACSMobility'><name>LDACS Mobility</name>
<t> <t>
LDACS supports layer 2 handovers to different LDACS cells. Hand LDACS supports Layer 2 handovers to different LDACS cells. Hand
overs may be initiated by the aircraft (break-before-make) or by the GS (make-be overs may be initiated by the aircraft (break-before-make) or by the GS (make-be
fore-break). Make-before-break handovers are only supported between GSs connect fore-break).
ed to each other, usually GS operated by the same service provider. Make-before-break handovers are only supported between GSs connected to each oth
er and usually GSs operated by the same service provider.
</t> </t>
<t> <t>
When a handover between AS and two interconnected GS takes place , it can be triggered by AS or GS. Once that is done, new security information i s exchanged between AS, GS1 and GS2, before the "old" connection is terminated b etween AS and GS1 and a "new" connection is set up between AS and GS2. As a last step, accumulated user-data at GS1 is forwarded to GS2 via a ground connection, before that is sent via GS2 to the AS. While some information for handover is t ransmitted in the LDACS DCH, the information remains in the "control-plane" part of LDACS and is exchanged between LMEs in AS, GS1 and GS2. As such, local mobi lity takes place entirely within the LDACS network, utilizing the PMIPv6 protoco l <xref target="RFC5213"/>. The use of PMIPv6 is currently not mandated by stand ardization, and may be vendor-specific. External handovers between non-connected LDACS access networks or different aeronautical data links are handled by the F CI multi-link concept. When a handover between the AS and two interconnected GSs takes place, it can be triggered by the AS or GS. Once that is done, new security info rmation is exchanged between the AS, GS1, and GS2 before the "old" connection is terminated between the AS and GS1 and a "new" connection is set up between the AS and GS2. As a last step, accumulated user data at GS1 is forwarded to GS2 via a ground connection before it is sent via GS2 to the AS. While some information for handover is transmitted in the LDACS DCH, the information remains in the "c ontrol plane" part of LDACS and is exchanged between LMEs in the AS, GS1, and G S2. As such, local mobility takes place entirely within the LDACS network and ut ilizes the PMIPv6 protocol <xref target="RFC5213"/>. The use of PMIPv6 is curren tly not mandated by standardization and may be vendor-specific. External handove rs between non-connected LDACS access networks or different aeronautical data li nks are handled by the FCI multilink concept.
</t> </t>
<t>
External handovers between non-connected LDACS access networks o
r different aeronautical data links are handled by the FCI multi- link concept.
</t>
</section> </section>
<section anchor='LDACSMng'><name>LDACS Management – Interfaces and Proto cols</name> <section anchor='LDACSMng'><name>LDACS Management Interfaces and Protoco ls</name>
<t> <t>
LDACS management interfaces and protocols are currently not be m andated by standardization. The implementations currently available use SNMP for management and Radius for AAA. Link state (link up, link down) is reported usin g the ATN/IPS Aircraft Protocol (AIAP) mandated by ICAO WG-I for multi-link. LDACS management interfaces and protocols are currently not be m andated by standardization. The implementations currently available use SNMP for management and Radius for Authentication, Authorization, and Accounting (AAA). Link state (link up, link down) is reported using the ATN/IPS Aircraft Protocol (AIAP) mandated by ICAO WG-I for multilink.
</t> </t>
</section> </section>
</section> </section>
<section anchor='ReliabilityandAvailability'><name>Reliability and Availabil ity</name> <section anchor='ReliabilityandAvailability'><name>Reliability and Availabil ity</name>
<section anchor='belowlone'><name>Below Layer 1</name> <section anchor='belowlone'><name>Below Layer 1</name>
<t> <t>
Below Layer 2, aeronautics usually relies on hardware redundancy . To protect availability of the LDACS link, an aircraft equipped with LDACS wi ll have access to two L-band antennae with triple redundant radio systems as req uired for any safety relevant aeronautical systems by ICAO. Below Layer 1, aeronautics usually rely on hardware redundancy. To protect availability of the LDACS link, an aircraft equipped with LDACS will have access to two L-band antennae with triple redundant radio systems as requi red for any safety relevant aeronautical systems by ICAO.
</t> </t>
</section> </section>
<section anchor='Layer2'><name>Layer 1 and 2</name> <section anchor='Layer2'><name>Layers 1 and 2</name>
<t> <t>
LDACS has been designed with applications related to the safety and regularity of flight in mind. It has therefore been designed as a determini stic wireless data link (as far as this is possible). LDACS has been designed with applications related to the safety and regularity of flight in mind; therefore, it has been designed as a determini stic wireless data link (as far as this is possible).
</t> </t>
<t> <t>
Based on channel measurements of the L-band channel LDACS was de signed from the PHY layer up with robustness in mind. Channel measurements of th e L-band channel <xref target="SCH2016"/> confirmed LDACS to be well adapted to its channel. Based on channel measurements of the L-band channel, LDACS was d esigned from the PHY layer up with robustness in mind. Channel measurements of t he L-band channel <xref target="SCH2016"/> confirmed LDACS to be well adapted to its channel.
</t> </t>
<t> <t>
In order to maximize the capacity per channel and to optimally u se the available spectrum, LDACS was designed as an OFDM-based FDD system, suppo rting simultaneous transmissions in FL in the G2A connection and RL in the A2G c onnection. The legacy systems already deployed in the L-band limit the bandwidt h of both channels to approximately 500 kHz. In order to maximize the capacity per channel and to optimally u se the available spectrum, LDACS was designed as an OFDM-based FDD system that s upports simultaneous transmissions in FL in the G2A connection and RL in the A2G connection. The legacy systems already deployed in the L-band limit the bandwi dth of both channels to approximately 500 kHz.
</t> </t>
<t> <t>
The LDACS physical layer design includes propagation guard times sufficient for operation at a maximum distance of 200 nautical miles from the G S. In actual deployment, LDACS can be configured for any range up to this maximu m range. The LDACS physical layer design includes propagation guard times sufficient for operation at a maximum distance of 200 nautical miles (nm) from the GS. In actual deployment, LDACS can be configured for any range up to this m aximum range.
</t> </t>
<t> <t>
The LDACS physical layer supports adaptive coding and modulation The LDACS physical layer supports adaptive coding and modulation
for user data. Control data is always encoded with the most robust coding and for user data.
modulation (FL: Quadrature Phase-Shift Keying (QPSK), coding rate 1/2, RL: QPSK, Control data is always encoded with the most robust coding and modulation (FL: Q
coding rate 1/3). uadrature Phase-Shift Keying (QPSK), coding rate 1/2; RL: QPSK, coding rate 1/3)
.
</t> </t>
<t> <t>
LDACS medium access layer on top of the physical layer uses a st LDACS medium access layer on top of the physical layer uses a st
atic frame structure to support deterministic timer management. As shown in <xr atic frame structure to support deterministic timer management.
ef target="fig_LDACSframesuper"/> and <xref target="fig_LDACSframesmulti"/>, LDA As shown in Figures <xref target="fig_LDACSframesuper" format="counter"/> and <x
CS framing structure is based on Super- Frames (SF) of 240ms duration correspond ref target="fig_LDACSframesmulti" format="counter"/>, LDACS framing structure is
ing to 2000 OFDM symbols. OFDM symbol time is 120 microseconds, sampling time 1. based on Super-Frames (SFs) of 240 ms (milliseconds) duration corresponding to
6 microseconds and a guard time of 4.8 microseconds. The structure of a SF is de 2000 OFDM symbols. OFDM symbol time is 120 microseconds, sampling time is 1.6 mi
picted in <xref target="fig_LDACSframesuper"/> along with its structure and timi croseconds, and guard time is 4.8 microseconds. The structure of an SF is depic
ngs of each part. FL and RL boundaries are aligned in time (from the GS perspect ted in <xref target="fig_LDACSframesuper"/> along with its structure and timings
ive) allowing for deterministic slots for control and data channels. This initi of each part. FL and RL boundaries are aligned in time (from the GS perspective
al AS time synchronization and time synchronization maintenance is based on obse ) allowing for deterministic slots for control and DCHs. This initial AS time s
rving the synchronization symbol pairs that repetitively occur within the FL str ynchronization and time synchronization maintenance is based on observing the sy
eam, being sent by the controlling GS <xref target="GRA2020"/>. As already menti nchronization symbol pairs that repetitively occur within the FL stream being se
oned, LDACS data transmission is split into user-data (DCH) and control (BCCH, C nt by the controlling GS <xref target="GRA2020"/>. As already mentioned, LDACS d
CCH in FL; RACH, DCCH in RL) as depicted with corresponding timings in <xref tar ata transmission is split into user data (DCH) and control (BCCH and CCCH in FL;
get="fig_LDACSframesmulti"/>. RACH and DCCH in RL) as depicted with corresponding timings in <xref target="fi
g_LDACSframesmulti"/>.
</t> </t>
<figure title="SF structure for LDACS" anchor="fig_LDACSframesuper"
> <figure title="SF Structure for LDACS" anchor="fig_LDACSframesuper"
<artwork> >
<![CDATA[ <artwork> <![CDATA[
^ ^
| +--------+------------+------------+------------+------------+ | +---------+------------+------------+------------+------------+
| FL | BCCH | MF | MF | MF | MF | | FL | BCCH | MF | MF | MF | MF |
| | 6.72ms | 58.32ms | 58.32ms | 58.32ms | 58.32ms | | | 6.72 ms | 58.32 ms | 58.32 ms | 58.32 ms | 58.32 ms |
F +--------+------------+------------+------------+------------+ F +---------+------------+------------+------------+------------+
r <----------------- Super-Frame (SF) - 240ms -----------------> r <----------------- Super-Frame (SF) - 240 ms ----------------->
e e
q +--------+------------+------------+------------+------------+ q +---------+------------+------------+------------+------------+
u RL | RACH | MF | MF | MF | MF | u RL | RACH | MF | MF | MF | MF |
e | 6.72ms | 58.32ms | 58.32ms | 58.32ms | 58.32ms | e | 6.72 ms | 58.32 ms | 58.32 ms | 58.32 ms | 58.32 ms |
n +--------+------------+------------+------------+------------+ n +---------+------------+------------+------------+------------+
c <----------------- Super-Frame (SF) - 240ms -----------------> c <----------------- Super-Frame (SF) - 240 ms ----------------->
y y
------------------------------ Time -------------------------------->
| |
]]> ]]></artwork>
</artwork>
</figure> </figure>
<figure title="MF Structure for LDACS" anchor="fig_LDACSframesmu
<figure title="MF structure for LDACS" anchor="fig_LDACSframesmu lti">
lti"> <artwork> <![CDATA[
<artwork>
<![CDATA[
^ ^
| +-------------+----------------+-----------------+ | +--------------+-----------------+------------------+
| FL | DCH | CCCH | DCH | | FL | DCH | CCCH | DCH |
| | 25.92ms | 2.16 - 17.28ms | 15.12 - 30.24ms | | | 25.92 ms | 2.16 - 17.28 ms | 15.12 - 30.24 ms |
F +-------------+----------------+-----------------+ F +--------------+-----------------+------------------+
r <----------- Multi-Frame (MF) - 58.32ms ---------> r <----------- Multiframe (MF) - 58.32 ms ----------->
e e
q +--------------+---------------------------------+ q +---------------+----------------------------------+
u RL | DCCH | DCH | u RL | DCCH | DCH |
e | 2.8 - 24.4ms | 33.84 - 55.44ms | e | 2.8 - 24.4 ms | 33.84 - 55.44 ms |
n +--------------+---------------------------------+ n +---------------+----------------------------------+
c <----------- Multi-Frame (MF) - 58.32ms ---------> c <----------- Multiframe (MF) - 58.32 ms ---------->
y y
----------------------------- Time ---------------------->
| |
]]> ]]></artwork>
</artwork> </figure>
</figure>
<t> <t>
LDACS cell entry is conducted with an initial control message exchange via the RACH and the BCCH. LDACS cell entry is conducted with an initial control message exchange via the RACH and the BCCH.
</t> </t>
<t> <t>
After cell entry, LDACS medium access is always under the contro l of the GS of a radio cell. Any medium access for the transmission of user dat a on a DCH has to be requested with a resource request message stating the reque sted amount of resources and class of service. The GS performs resource schedul ing on the basis of these requests and grants resources with resource allocation messages. Resource request and allocation messages are exchanged over dedicate d contention-free control channels (DCCH and CCCH). After cell entry, LDACS medium access is always under the contro l of the GS of a radio cell. Any medium access for the transmission of user dat a on a DCH has to be requested with a resource request message stating the reque sted amount of resources and class of service. The GS performs resource schedul ing on the basis of these requests and grants resources with resource allocation messages. Resource request and allocation messages are exchanged over dedicate d contention-free control channels (DCCH and CCCH).
</t> </t>
<t> <t>
The purpose of quality-of-service in LDACS medium access is to p rovide prioritized medium access at the bottleneck (the wireless link). Signalin g of higher layer quality-of-service requests to LDACS is implemented on the bas is of Differentiated Services-(DiffServ) classes CS01 (lowest priority) to CS07 (highest priority). The purpose of QoS in LDACS medium access is to provide prioriti zed medium access at the bottleneck (the wireless link). Signaling of higher-lay er QoS requests to LDACS is implemented on the basis of Differentiated Services (Diffserv) classes CS01 (lowest priority) to CS07 (highest priority).
</t> </t>
<t> <t>
In addition to having full control over resource scheduling, the GS can send forced handover commands for off-loading or channel management, e.g ., when the signal quality declines and a more suitable GS is in the AS's reach. With robust resource management of the capacities of the radio channel, reliab ility and robustness measures are therefore also anchored in the LME. In addition to having full control over resource scheduling, the GS can send forced handover commands for off-loading or channel management, e.g ., when the signal quality declines and a more suitable GS is in the AS's reach. With robust resource management of the capacities of the radio channel, reliab ility and robustness measures are also anchored in the LME.
</t> </t>
<t> <t>
In addition to radio resource management, the LDACS control chan nels are also used to send keep-alive messages, when they are not otherwise used . Since the framing of the control channels is deterministic, missing keep-aliv e messages can thus be immediately detected. This information is made available to the multilink protocols for fault management. In addition to radio resource management, the LDACS control chan nels are also used to send keepalive messages when they are not otherwise used. Since the framing of the control channels is deterministic, missing keepalive m essages can be immediately detected. This information is made available to the multilink protocols for fault management.
</t> </t>
<t> <t>
The protocol used to communicate faults is not defined in the LD The protocol used to communicate faults is not defined in the LD
ACS specification. It is assumed that vendors would use industry standard proto ACS specification. It is assumed that vendors would use industry standard proto
cols like the Simple Network Management Protocol or the Network Configuration Pr cols like the Simple Network Management Protocol or the Network Configuration Pr
otocol, where security permits. otocol (NETCONF) where security permits.
</t>
<t>
The LDACS data link layer protocol, running on top of the medium
access sub-layer, uses ARQ to provide reliable data transmission on the data ch
annel.
</t> </t>
<t> <t>
It employs selective repeat ARQ with transparent fragmentation a nd reassembly to the resource allocation size to minimize latency and overhead w ithout losing reliability. It ensures correct order of packet delivery without d uplicates. In case of transmission errors, it identifies lost fragments with de terministic timers synced to the medium access frame structure and initiates ret ransmission. The LDACS data link layer protocol, running on top of the medium access sub-layer, uses ARQ to provide reliable data transmission on the DCH. It employs selective repeat ARQ with transparent fragmentation and reassembly to t he resource allocation size to minimize latency and overhead without losing reli ability. It ensures correct order of packet delivery without duplicates. In cas e of transmission errors, it identifies lost fragments with deterministic timers synced to the medium access frame structure and initiates retransmission.
</t> </t>
</section> </section>
<section anchor='BeyondLayer2'><name>Beyond Layer 2</name> <section anchor='BeyondLayer2'><name>Beyond Layer 2</name>
<t> <t>
LDACS availability can be increased by appropriately deploying L DACS infrastructure: This means proliferating the number of terrestrial ground s tations. However, there are four aspects that need to be taken into considerati on: (1) scarcity of aeronautical spectrum for data link communication (in the ca se of LDACS: tens of MHz in the L-band), (2) an increase in the amount of ground stations also increases the individual bandwidth for aircraft in the cell, as f ewer aircraft have to share the spectrum, (3) to cover worldwide terrestrial ATM via LDACS is also a question of cost and the possible reuse of spectrum which m akes it not always possible to decrease cell sizes and (4) the Distance Measurin g Equipment (DME) is the primary user of the aeronautical L-band, which means an y LDACS deployment has to take DME frequency planning into account. LDACS availability can be increased by appropriately deploying L DACS infrastructure. This means proliferating the number of terrestrial GSs. Ho wever, there are four aspects that need to be taken into consideration: (1) scar city of aeronautical spectrum for data link communication (tens of MHz in the L- band in the case of LDACS), (2) an increase in the number of GSs also increases the individual bandwidth for aircraft in the cell, as fewer aircraft have to sha re the spectrum, (3) covering worldwide terrestrial ATM via LDACS is also a ques tion of cost and the possible reuse of spectrum, which makes it not always possi ble to decrease cell sizes, and (4) the Distance Measuring Equipment (DME) is th e primary user of the aeronautical L-band, which means any LDACS deployment has to take DME frequency planning into account.
</t> </t>
<t> <t>
While aspect (2) provides a good reason, alongside increasing re dundancy, for smaller cells than the maximum range LDACS was developed for (200 Nautical Miles (NM)), the other three need to be respected when doing so. There are preliminary works on LDACS cell planning, such as <xref target="MOST2018"/>, where the authors reach the conclusion that 84 LDACS cells in Europe would be s ufficient to serve European air traffic for the next 20 years. While aspect (2) provides a good reason alongside increasing red undancy for smaller cells than the maximum range LDACS was developed for (200 nm ), the other three need to be respected when doing so. There are preliminary wor ks on LDACS cell planning, such as <xref target="MOST2018"/>, where the authors concluded that 84 LDACS cells in Europe would be sufficient to serve European ai r traffic for the next 20 years.
</t> </t>
<t> <t>
For redundancy reasons, the aeronautical community has decided n ot to rely on a single communication system or frequency band. It is envisioned to have multiple independent data link technologies in the aircraft (e.g., terr estrial and satellite communications) in addition to legacy VHF voice. For redundancy reasons, the aeronautical community has decided n ot to rely on a single communication system or frequency band. It is envisioned to have multiple independent data link technologies in the aircraft (e.g., terr estrial and satellite communications) in addition to legacy VHF voice.
</t> </t>
<t> <t>
However, as of now, no reliability and availability mechanisms t hat could utilize the multilink architecture, have been specified on Layer 3 and above. Even if LDACS has been designed for reliability, the wireless medium pr esents significant challenges to achieve deterministic properties such as low pa cket error rate, bounded consecutive losses, and bounded latency. Support for h igh reliability and availability for IP connectivity over LDACS is certainly hig hly desirable but needs to be adapted to the specific use case. However, as of now, no reliability and availability mechanisms t hat could utilize the multilink architecture have been specified on Layer 3 and above. Even if LDACS has been designed for reliability, the wireless medium pre sents significant challenges to achieve deterministic properties such as low pac ket error rate, bounded consecutive losses, and bounded latency. Support for hi gh reliability and availability for IP connectivity over LDACS is highly desirab le, but support needs to be adapted to the specific use case.
</t> </t>
</section> </section>
</section> </section>
<section anchor='Security2'><name>Security Considerations</name>
<section anchor='Security2'><name>Security</name>
<t> <t>
The goal of this Section is to inform the reader about the state of security in aeronautical communications, state security considerations appli cable for all ATN/IPS traffic and to provide an overview of the LDACS link-layer security capabilities. The goal of this section is to inform the reader about the state of security in aeronautical communications and the state security consideration s applicable for all ATN/IPS traffic and to provide an overview of the LDACS lin k-layer security capabilities.
</t> </t>
<section anchor='Resasons'><name>Security in Wireless Digital Aerona utical Communications</name> <section anchor='Resasons'><name>Security in Wireless Digital Aerona utical Communications</name>
<t> <t>
Aviation will require secure exchanges of data and voice mes sages for managing the air traffic flow safely through the airspaces all over th e world. Historically Communication Navigation Surveillance (CNS) wireless commu nications technology emerged from the military and a threat landscape where infe rior technological and financial capabilities of adversaries were assumed <xref target="STR2016"/>. The main communications method for ATC today is still an ope n analogue voice broadcast within the aeronautical VHF band. Currently, informa tion security is mainly procedural, based by using well-trained personnel and pr oven communications procedures. This communication method has been in service s ince 1948. However, since the emergence of civil aeronautical CNS applications in the 70s, and today, the world has changed. Aviation will require secure exchanges of data and voice mes sages for managing the air traffic flow safely through the airspaces all over th e world. Historically, Communication Navigation Surveillance (CNS) wireless comm unications technology emerged from the military and a threat landscape where inf erior technological and financial capabilities of adversaries were assumed <xref target="STR2016"/>. The main communications method for ATC today is still an op en analog voice broadcast within the aeronautical VHF band. Currently, informat ion security is mainly procedural and based by using well-trained personnel and proven communications procedures. This communication method has been in service since 1948. However, the world has changed since the emergence of civil aerona utical CNS applications in the 70s.
</t> </t>
<t> <t>
CCivil applications have significant lower spectrum availabl Civil applications have significant lower spectrum available
e than military applications. This means several military defense mechanisms, than military applications.
such as frequency hopping or pilot symbol scrambling and, thus, a defense-in-de This means that several military defense mechanisms such as frequency hopping or
pth approach starting at the physical layer, is infeasible for civil systems. Wi pilot symbol scrambling (and thus a defense-in-depth approach starting at the p
th the rise of cheap Software Defined Radios (SDR), the previously existing fina hysical layer) are infeasible for civil systems. With the rise of cheap Software
ncial barrier is almost gone and open source projects such as GNU radio <xref ta -Defined Radios (SDRs), the previously existing financial barrier is almost gone
rget="GNU2021"/> allow a new type of unsophisticated listeners and possible atta , and open source projects such as GNU radio <xref target="GNU2021"/> allow for
ckers. a new type of unsophisticated listener and possible attacker.
</t> </t>
<t> <t>
Most CNS technology developed in ICAO relies on open standar Most CNS technology developed in ICAO relies on open standar
ds, thus syntax and semantics of wireless digital aeronautical communications sh ds; thus, syntax and semantics of wireless digital aeronautical communications s
ould be expected to be common knowledge for attackers. With increased digitizat hould be expected to be common knowledge for attackers.
ion and automation of civil aviation, the human as control instance, is being ta With increased digitization and automation of civil aviation, the human as contr
ken gradually out of the loop. Autonomous transport drones or single piloted ai ol instance is being taken gradually out of the loop. Autonomous transport dron
rcraft demonstrate this trend. However, without profound cybersecurity measures es or single-piloted aircraft demonstrate this trend. However, without profound
such as authenticity and integrity checks of messages in-transit on the wireless cybersecurity measures, such as authenticity and integrity checks of messages in
link or mutual entity authentication, this lack of a control instance can prove -transit on the wireless link or mutual entity authentication, this lack of a co
disastrous. Thus, future digital communications will need additional embedded ntrol instance can prove disastrous. Thus, future digital communications will n
security features to fulfill modern information security requirements like authe eed additional embedded security features to fulfill modern information security
ntication and integrity. requirements like authentication and integrity.
These security features require sufficient bandwidth which i s beyond the capabilities of currently deployed VHF narrowband communications sy stems. For voice and data communications, sufficient data throughput capability is needed to support the security functions while not degrading performance. L DACS is a data link technology with sufficient bandwidth to incorporate security without losing too much user data throughput. These security features require sufficient bandwidth, which is beyond the capabilities of currently deployed VHF narrowband communications s ystems. For voice and data communications, sufficient data throughput capabilit y is needed to support the security functions while not degrading performance. LDACS is a data link technology with sufficient bandwidth to incorporate securit y without losing too much user data throughput.
</t> </t>
</section> </section>
<section anchor='Secdepth'><name>Security in Depth </name> <section anchor='Secdepth'><name>Security in Depth</name>
<t> <t>
ICAO Doc 9896 foresees transport layer security <xref target
="ICAO2015"/> for all aeronautical data transmitted via the ATN/IPS, as describe ICAO Doc 9896 <xref target="ICAO2015"/> foresees transport l
d in ARINC P858 <xref target="ARI2021"/>. This is realized via Datagram Transpor ayer security for all aeronautical data transmitted via the ATN/IPS, as describe
t Layer Security (DTLS) 1.3 <xref target="RFC9147"/>. d in ARINC 858 <xref target="ARI2021"/>. This is realized via Datagram Transport
Layer Security (DTLS) 1.3 <xref target="RFC9147"/>.
</t> </t>
<t> <t>
LDACS also needs to comply with in-depth security requiremen LDACS also needs to comply with in-depth security requirements a
ts, stated in ARINC 858, for the radio access technologies transporting ATN/IPS s stated in ARINC 858 for the radio access technologies transporting ATN/IPS dat
data. These requirements imply that LDACS must provide layer 2 security in addi a. These requirements imply that LDACS must provide Layer 2 security in additio
tion to any higher layer mechanisms. Specifically, ARINC 858 states that [datali n to any higher-layer mechanisms. Specifically, ARINC 858 <xref target="ARI2021"
nks within the FCI need to provide] "a secure channel between the airborne radio /> states that data links within the FCI need to provide</t>
systems and the peer radio access endpoints on the ground [...] to ensure authe <blockquote>a secure channel between the airborne radio systems and the peer rad
ntication and integrity of air-ground message exchanges in support of an overall io access endpoints on the ground [...] to ensure authentication and integrity o
defense-in-depth security strategy." <xref target="ARI2021"/> f air-ground message exchanges in support of an overall defense-in-depth securit
</t> y strategy.
</blockquote>
</section> </section>
<section anchor='Requirements'><name>LDACS Security Requirements </n ame> <section anchor='Requirements'><name>LDACS Security Requirements </n ame>
<t> <t>
Overall, cybersecurity for CNS technology shall protect the following business goals <xref target="MAE20181"/>: Overall, cybersecurity for CNS technology shall protect the following business goals <xref target="MAE20181"/>:
</t><dl spacing='compact'> </t><ol spacing='compact'>
<dt>1.</dt><dd> <li>Safety: The system must sufficiently mitigate attack
Safety: The system must sufficiently mitigate attacks, w s that contribute to safety hazards.</li>
hich contribute to safety hazards.</dd> <li>Flight regularity: The system must sufficiently
<dt>2.</dt><dd> mitigate attacks that contribute to delays, diversions, o
Flight regularity: The system must sufficiently mitigate r cancelations of flights.
attacks, which contribute to delays, diversions, or cancellations of flights. </li>
</dd> <li>Protection of business interests: The system must su
<dt>3.</dt><dd> fficiently mitigate attacks that result in financial loss, reputation damage, di
Protection of business interests: The system must suffic sclosure of sensitive proprietary information, or disclosure of personal informa
iently mitigate attacks which result in financial loss, reputation damage, discl tion.
osure of sensitive proprietary information, or disclosure of personal informatio </li>
n. </ol><t>
</dd>
</dl><t>
</t> </t>
<t> <t>
To further analyze assets and derive threats and thus protec To further analyze assets, derive threats, and create protect
tion scenarios several threat-and risk analyses were performed for LDACS <xref t ion scenarios, several threat and risk analyses were performed for LDACS <xref t
arget="MAE20181"/> , <xref target="MAE20191"/>. These results allowed the deriva arget="MAE20181"/> <xref target="MAE20191"/>. These results allowed the derivati
tion of security scope and objectives from the requirements and the conducted th on of security scope and objectives from the requirements and the conducted thre
reat-and risk analysis. Note, IPv6 security considerations are briefly discussed at and risk analysis. Note, IPv6 security considerations are briefly discussed i
in <xref target="cons"/> while a summary of security requirements for link-laye n <xref target="cons"/> while a summary of security requirements for link-layer
r candidates in the ATN/IPS is given in <xref target="ARI2021"/>, which states: candidates in the ATN/IPS is given in <xref target="ARI2021"/>, which states:</t
"Since the communication radios connect to local airborne networks in the aircra >
ft control domain, [...] the airborne radio systems represent the first point of <blockquote>
entry for an external threat to the aircraft. Consequently, a secure channel be Since the communication radios connect to local airborne networks in the aircraf
tween the airborne radio systems and the peer radio access endpoints on the grou t control domain, [...] the airborne radio systems represent the first point of
nd is necessary to ensure authentication and integrity of air-ground message exc entry for an external threat to the aircraft. Consequently, a secure channel bet
hanges in support of an overall defense-in-depth security strategy". ween the airborne radio systems and the peer radio access endpoints on the groun
</t> d is necessary to ensure authentication and integrity of air-ground message exch
anges in support of an overall defense-in-depth security strategy.
</blockquote>
</section> </section>
<section anchor='objectives'><name>LDACS Security Objectives</name> <section anchor='objectives'><name>LDACS Security Objectives</name>
<t> <t>
Security considerations for LDACS are defined by the officia l SARPS document by ICAO <xref target="ICAO2022"/>: Security considerations for LDACS are defined by the officia l SARPS document by ICAO <xref target="ICAO2022"/>:
</t><dl spacing='compact'> </t><ul spacing='compact'>
<dt>1.</dt><dd> <li>LDACS shall provide a capability to protect the avai
LDACS shall provide a capability to protect the availabi lability and continuity of the system.</li>
lity and continuity of the system.</dd> <li>LDACS shall provide a capability including cryptogra
<dt>2.</dt><dd> phic mechanisms to protect the integrity of messages in transit.
LDACS shall provide a capability including cryptographic </li>
mechanisms to protect the integrity of messages in transit. <li>LDACS shall provide a capability to ensure the authentic
</dd> ity of messages in transit.
<dt>3.</dt><dd> </li>
LDACS shall provide a capability to ensure the authentic <li>LDACS should provide a capability for non-repudiation of
ity of messages in transit. origin for messages in transit.
</dd> </li>
<dt>4.</dt><dd> <li>LDACS should provide a capability to protect the confide
LDACS should provide a capability for nonrepudiation of ntiality of messages in transit.
origin for messages in transit. </li>
</dd> <li>LDACS shall provide an authentication capability.
<dt>5.</dt><dd> </li>
LDACS should provide a capability to protect the confide <li>LDACS shall provide a capability to authorize the permi
ntiality of messages in transit. tted actions of users of the system and to deny actions that are not explicitly
</dd> authorized.
<dt>6.</dt><dd> </li>
LDACS shall provide an authentication capability. <li>If LDACS provides interfaces to multiple domains, LDACS
</dd> shall provide capability to prevent the propagation of intrusions within LDACS
<dt>7.</dt><dd> domains and towards external domains.
LDACS shall provide a capability to authorize the permit </li>
ted actions of users of the system and to deny actions that are not explicitly a </ul><t>
uthorized.
</dd>
<dt>8.</dt><dd>
If LDACS provides interfaces to multiple domains, LDACS
shall provide capability to prevent the propagation of intrusions within LDACS d
omains and towards external domains.
</dd>
</dl><t>
</t> </t>
<t> <t>
Work in 2022 includes a change request for these SARPS a ims to limit the “non-repudiation of origin of messages in transit” requirement only to the authentication and key establishment messages at the beginning of ev ery session. Work in 2022 includes a change request for these SARPS a ims to limit the "non-repudiation of origin of messages in transit" requirement only to the authentication and key establishment messages at the beginning of ev ery session.
</t> </t>
</section> </section>
<section anchor='SFL'><name>LDACS Security Functions</name> <section anchor='SFL'><name>LDACS Security Functions</name>
<t> <t>
These objectives were used to derive several security functi ons for LDACS required to be integrated in the LDACS cybersecurity architecture: Identification, Authentication, Authorization, Confidentiality, System Integrit y, Data Integrity, Robustness, Reliability, Availability, and Key and Trust Ma nagement. Several works investigated possible measures to implement these secur ity functions <xref target="BIL2017"/>, <xref target="MAE20181"/>, <xref target= "MAE20191"/>. These objectives were used to derive several security functi ons for LDACS required to be integrated in the LDACS cybersecurity architecture: Identification, Authentication, Authorization, Confidentiality, System Integrit y, Data Integrity, Robustness, Reliability, Availability, and Key and Trust Ma nagement. Several works investigated possible measures to implement these secur ity functions <xref target="BIL2017"/> <xref target="MAE20181"/> <xref target="M AE20191"/>.
</t> </t>
</section> </section>
<section anchor='SADL'><name>LDACS Security Architecture</name> <section anchor='SADL'><name>LDACS Security Architecture</name>
<t> <t>
The requirements lead to a LDACS security model, including d ifferent entities for identification, authentication and authorization purposes, ensuring integrity, authenticity and confidentiality of data. A draft of the cy bersecurity architecture of LDACS can be found in <xref target="ICAO2022"/> and <xref target="MAE20182"/> and respective updates in <xref target="MAE20191"/>, < xref target="MAE20192"/>, <xref target="MAE2020"/>, <xref target="MAE2021"/>. The requirements lead to an LDACS security model, including di fferent entities for identification, authentication, and authorization purposes ensuring integrity, authenticity, and confidentiality of data. A draft of the cy bersecurity architecture of LDACS can be found in <xref target="ICAO2022"/> and <xref target="MAE20182"/>, and respective updates can be found in <xref target=" MAE20191"/>, <xref target="MAE20192"/>, <xref target="MAE2020"/>, and <xref targ et="MAE2021"/>.
</t> </t>
<section anchor='ELSM'><name>Entities </name> <section anchor='ELSM'><name>Entities </name>
<t> <t>
A simplified LDACS architectural model requires the foll owing entities: Network operators such as the Societe Internationale de Telecomm unications Aeronautiques (SITA) <xref target="SIT2020"/> and ARINC <xref target= "ARI2020"/> are providing access to the ground IPS network via an A/G LDACS ro uter. This router is attached to an internal LDACS access network, which conne cts via further access routers to the different LDACS cell ranges, each control led by a GS (serving one LDACS cell), with several interconnected GS spanning a local LDACS access network. Via the A/G wireless LDACS data link AS the aircr aft is connected to the ground network and via the aircraft's VI and aircraft's network interface, aircraft's data can be sent via the AS back to the GS, then to the LDACS local access network, access routers, LDACS access network, A/G LDA CS router and finally to the ground IPS network <xref target="ICAO2015"/>. A simplified LDACS architectural model requires the foll owing entities: network operators such as the Societe Internationale de Telecomm unications Aeronautiques (SITA) <xref target="SIT2020"/> and ARINC <xref target= "ARI2020"/>; both entities provide access to the ground IPS network via an A/G L DACS router. This router is attached to an internal LDACS access network that c onnects via further AC-Rs to the different LDACS cell ranges, each controlled by a GS (serving one LDACS cell), with several interconnected GSs spanning a local LDACS access network. Via the A/G wireless LDACS data link AS, the aircraft i s connected to the ground network. Via the aircraft's VI and network interface, the aircraft's data can be sent via the AS back to the GS, then to the LDACS loc al access network, AC-Rs, LDACS access network, A/G LDACS router, and finally to the ground IPS network <xref target="ICAO2015"/>.
</t> </t>
</section> </section>
<section anchor='MLEI'><name>Entity Identification</name> <section anchor='MLEI'><name>Entity Identification</name>
<t> <t>
LDACS needs specific identities for the AS, the GS, and the network operator. The aircraft itself can be identified using the 24-bit ICAO identifier of an aircraft <xref target="ICAO2022"/>, the call sign of that aircraft or the recently founded privacy ICAO address of the Federal Aviation A dministration (FAA) program with the same name <xref target="FAA2020"/>. It is conceivable that the LDACS AS will use a combination of aircraft identification, radio component identification and even operator feature identification to crea te a unique AS LDACS identification tag. Similar to a 4G's eNodeB serving netwo rk identification tag, a GS could be identified using a similar field. The iden tification of the network operator is again similar to 4G (e.g., E-Plus, AT&amp; T, and TELUS), in the way that the aeronautical network operators are listed (e. g., ARINC <xref target="ARI2020"/> and SITA <xref target="SIT2020"/>). LDACS needs specific identities for the AS, the GS, and the network operator. The aircraft itself can be identified using the 24-bit IC AO identifier of an aircraft <xref target="ICAO2022"/>, the call sign of that ai rcraft, or the recently founded privacy ICAO address of the Federal Aviation Adm inistration (FAA) program with the same name <xref target="FAA2020"/>. It is co nceivable that the LDACS AS will use a combination of aircraft identification, r adio component identification, and even operator feature identification to creat e a unique LDACS AS identification tag. Similar to a 4G's eNodeB-serving networ k identification tag, a GS could be identified using a similar field. The ident ification of the network operator is similar to 4G (e.g., E-Plus, AT&amp;T, and TELUS), in the way that the aeronautical network operators are listed (e.g., ARI NC <xref target="ARI2020"/> and SITA <xref target="SIT2020"/>).
</t> </t>
</section> </section>
<section anchor='MLEIAKN'><name>Entity Authentication and Key Es tablishment</name> <section anchor='MLEIAKN'><name>Entity Authentication and Key Es tablishment</name>
<t> <t>
In order to anchor trust within the system, all LDACS en tities connected to the ground IPS network will be rooted in an LDACS specific c hain-of-trust and PKI solution, quite similar to AeroMACS’s approach <xref targe t="CRO2016"/>. These certificates, residing at the entities and incorporated in the LDACS PKI, providing proof the ownership of their respective public key, inc lude information about the identity of the owner and the digital signature of th e entity that has verified the certificate's content. First, all ground infrast ructures must mutually authenticate to each other, negotiate and derive keys and , thus, secure all ground connections. How this process is handled in detail is still an ongoing discussion. However, established methods to secure user plane b y IPSec <xref target="RFC4301"/> and IKEv2 <xref target="RFC7296"/> or the appli cation layer via TLS 1.3 <xref target="RFC8446"/> are conceivable. The LDACS PKI with its chain-of-trust approach, digital certificates and public entity keys l ay the groundwork for this step. In a second step, the AS with the LDACS radio a board, approaches an LDACS cell and performs a cell-attachment procedure with th e corresponding GS. This procedure consists of (1) the basic cell entry <xref ta rget="GRA2020"/> and (2) a Mutual Authentication and Key Establishment (MAKE) pr ocedure <xref target="MAE2021"/>. In order to anchor trust within the system, all LDACS en tities connected to the ground IPS network will be rooted in an LDACS-specific c hain-of-trust and PKI solution, quite similar to AeroMACS's approach <xref targe t="CRO2016"/>. These certificates, residing at the entities and incorporated in the LDACS PKI, provide proof of the ownership of their respective public key and include information about the identity of the owner and the digital signature o f the entity that has verified the certificate's content. First, all ground inf rastructures must mutually authenticate to each other, negotiate and derive keys , and then secure all ground connections. How this process is handled in detail is still an ongoing discussion. However, established methods to secure the user plane by IPsec <xref target="RFC4301"/> and IKEv2 <xref target="RFC7296"/> or th e application layer via TLS 1.3 <xref target="RFC8446"/> are conceivable. The LD ACS PKI with its chain-of-trust approach, digital certificates, and public entit y keys lay the groundwork for this step. In a second step, the AS with the LDACS radio aboard approaches an LDACS cell and performs a cell-attachment procedure with the corresponding GS. This procedure consists of (1) the basic cell entry < xref target="GRA2020"/> and (2) a MAKE procedure <xref target="MAE2021"/>.
</t> </t>
<t> <t>
Note that LDACS will foresee multiple security levels. T Note that LDACS will foresee multiple security levels. T
o address the issue of the long service life of LDACS (i.e., possibly &gt;30 yea o address the issue of the long service life of LDACS (i.e., possibly greater th
rs) and the security of current pre-quantum cryptography, these security levels an 30 years) and the security of current pre-quantum cryptography, these securit
include pre- and post-quantum cryptographic solutions. Limiting security data on y levels include pre-quantum and post-quantum cryptographic solutions.
the LDACS datalink as much as possible, to reserve as much space for actual use Limiting security data on the LDACS data link as much as possible to reserve as
r data transmission, is key in the LDACS security architecture, this is also ref much space for actual user data transmission is key in the LDACS security archit
lected in the underlying cryptography: Pre-quantum solutions will rely on ellipt ecture. This is also reflected in the underlying cryptography.
ic curves <xref target="NIST2013"/>, while post-quantum solutions consider Falco Pre-quantum solutions will rely on elliptic curves <xref target="NIST2013"/>, wh
n <xref target="SON2021"/> <xref target="MAE2021"/> or similar lightweight PQC s ile post-quantum solutions consider Falcon <xref target="SON2021"/> <xref target
ignature schemes, and CRYSTALS-KYBER or SABER as key establishment options <xref ="MAE2021"/> or similar lightweight PQC signature schemes and CRYSTALS-KYBER or
target="AVA2021"/> <xref target="ROY2020"/>. SABER as key establishment options <xref target="AVA2021"/> <xref target="ROY202
0"/>.
</t> </t>
</section> </section>
<section anchor='MLCIA'><name>Message-in-transit Confidentiality , Integrity and Authenticity</name> <section anchor='MLCIA'><name>Message-In-Transit Confidentiality , Integrity, and Authenticity</name>
<t> <t>
The key material from the previous step can then be used to protect LDACS Layer 2 communications via applying encryption and integrity p rotection measures on the SNP layer of the LDACS protocol stack. As LDACS transp orts AOC and ATS data, the integrity of that data is most important, while confi dentiality only needs to be applied to AOC data to protect business interests <x ref target="ICAO2022"/>. This possibility of providing low layered confidentiali ty and integrity protection ensures a secure delivery of user data over the wire less link. Furthermore, it ensures integrity protection of LDACS control data. The key material from the previous step can then be used to protect LDACS Layer 2 communications via applying encryption and integrity p rotection measures on the SNP layer of the LDACS protocol stack. As LDACS transp orts AOC and ATS data, the integrity of that data is most important while confid entiality only needs to be applied to AOC data to protect business interests <xr ef target="ICAO2022"/>. This possibility of providing low-layered confidentialit y and integrity protection ensures a secure delivery of user data over the wirel ess link. Furthermore, it ensures integrity protection of LDACS control data.
</t> </t>
</section> </section>
</section> </section>
<section anchor='cons'><name>Considerations on LDACS Security Impact on IPv6 Operational Security</name> <section anchor='cons'><name>Considerations on LDACS Security Impact on IPv6 Operational Security</name>
<t> <t>
In this part, considerations on IPv6 operational security in In this part, considerations on IPv6 operational security in
<xref target="RFC9099"/> and interrelations with the LDACS security additions a <xref target="RFC9099"/> and interrelations with the LDACS security additions a
re compared and evaluated to identify further protection demands. As IPv6 heavil re compared and evaluated to identify further protection demands. As IPv6 heavil
y relies on the Neighbor Discovery Protocol (NDP) <xref target="RFC4861"/>, inte y relies on the Neighbor Discovery Protocol (NDP) <xref target="RFC4861"/>, inte
grity and authenticity protection on the link-layer, as provided by LDACS, alrea grity and authenticity protection on the link layer, as provided by LDACS, alrea
dy help mitigate spoofing and redirection attacks. However, to also mitigate the dy help mitigate spoofing and redirection attacks. However, to also mitigate the
threat of remote DDoS attacks, neighbor solicitation rate-limiting is recommend threat of remote DDoS attacks, neighbor solicitation rate-limiting is recommend
ed by RFC 9099. To prevent the threat of (D)DoS attacks in general on the LDACS ed by <xref
access network, rate-limiting needs to be performed on each network node in the target="RFC9099"/>. To prevent the threat of DDoS and DoS attacks in general on
LDACS access network. One approach is to filter for the total amount of possible the LDACS access network, rate-limiting needs to be performed on each network no
LDACS AS-GS traffic per cell – i.e., of up to 1.4 Mbps user-data per cell and u de in the LDACS access network. One approach is to filter for the total amount o
p to the amount of GS per service provider network times 1.4 Mbps. f possible LDACS AS-GS traffic per cell (i.e., of up to 1.4 Mbit/s user data per
cell and up to the amount of GS per service provider network times 1.4 Mbit/s).
</t> </t>
</section> </section>
</section> </section>
<!-- Possibly a 'Contributors' section ... -->
<section anchor='IANA'><name>IANA Considerations</name> <section anchor='IANA'><name>IANA Considerations</name>
<t>This memo includes no request to IANA.</t> <t>This document has no IANA actions.</t>
</section>
<section anchor='Acknowledgements'><name>Acknowledgements</name>
<t>
Thanks to all contributors to the development of LDACS and ICAO
PT-T, as well as to all in the RAW Working Group for deep discussions and feedba
ck.
</t>
<t>
Thanks to Klaus-Peter Hauf, Bart Van Den Einden, and Pierluigi F
antappie for their comments to this draft.
</t>
<t>
Thanks to the Chair for Network Security and the research instit
ute CODE for their comments and improvements.
</t>
<t>
Thanks to the colleagues of the Research Institute CODE at the U
niBwM working in the AMIUS project funded under the Bavarian Aerospace Program b
y the Bavarian State Ministry of Economics, Regional Development and Energy with
the GA ROB-2-3410.20-04-11-15/HAMI-2109-0015 for fruitful discussions on aerona
utical communications and relevant security incentives for the target market.
</t>
<t>
Thanks to SBA Research Vienna for continuous discussions on secu
rity infrastructure issues in quick developing markets such the air space and po
tential economic spillovers to used technologies and protocols.
</t>
<t>
Thanks to the Aeronautical Communications group at the Institute
of Communications and Navigation of the German Aerospace Center (DLR). With tha
t, the authors would like to explicitly thank Miguel Angel Bellido-Manganell and
Lukas Marcel Schalk for their thorough feedback.
</t>
</section> </section>
</middle> </middle>
<!-- *****BACK MATTER ***** -->
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eference.RFC.7296.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/r 446.xml"/>
eference.RFC.8200.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.9
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/r 099.xml"/>
eference.RFC.8446.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.9
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/r 147.xml"/>
eference.RFC.9099.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/r
eference.RFC.9147.xml"/>
<reference anchor="GRA2020" target="https://www.ldacs.com/wp-content /uploads/2013/12/SESAR2020_PJ14-W2-60_D3_1_210_Initial_LDACS_AG_Specification_00 _01_00-1_0_updated.pdf"> <!--REF3--> <reference anchor="GRA2020" target="https://www.ldacs.com/wp-content/uploads/201 3/12/SESAR2020_PJ14-W2-60_D3_1_210_Initial_LDACS_AG_Specification_00_01_00-1_0_u pdated.pdf">
<front> <front>
<title>LDACS A/G Specification <title>Initial LDACS A/G Specification</title>
</title>
<author initials="T." surname="Gräupl"/> <author initials="T." surname="Gräupl"/>
<author initials="C." surname="Rihacek"/> <date month="December" year="2020"/>
<author initials="B." surname="Haindl"/>
<date year="2020"/>
</front> </front>
<seriesInfo name='SESAR2020 PJ14-02-01 D3.3.030' value=''/> <seriesInfo name='SESAR2020 -' value='PJ14-W2-60, D3.1.210'/>
</reference> </reference>
<reference anchor="ARI2021" target="https://standards.globalspec.com /std/14391274/858p1"> <reference anchor="ARI2021" target="https://standards.globalspec.com /std/14391274/858p1">
<front> <front>
<title>Internet Protocol Suite (IPS) For Aeronautical Safety Services Part 1- Airborne IP System Technical Requirements, ARINC SPECIFICATION 858 P1</title> <title>INTERNET PROTOCOL SUITE (IPS) FOR AERONAUTICAL SAFETY SERVICES PART 1 AIRBORNE IPS SYSTEM TECHNICAL REQUIREMENTS</title>
<author> <author>
<organization>ARINC</organization> <organization>ARINC</organization>
</author> </author>
<date year="2021" month="June"/> <date year="2021" month="June"/>
</front> </front>
<seriesInfo name="ARINC" value="858P1"/>
</reference> </reference>
<reference anchor="EURO2019" target="https://eshop.eurocae.net/euroc ae-documents-and-reports/ed-262/"> <reference anchor="EURO2019" target="https://eshop.eurocae.net/euroc ae-documents-and-reports/ed-262/">
<front> <front>
<title>Technical Standard of Aviation Profiles for ATN/IPS <title>Technical Standard of Aviation Profiles
, ED-262 for ATN/IPS
</title> </title>
<author> <author>
<organization>European Organization for Civil Aviation Equipment (EUROCAE)</organization> <organization>European Organization for Civil Aviation Equipment (EUROCAE)</organization>
</author> </author>
<date year="2019" month="September"/> <date year="2019" month="September"/>
</front> </front>
<seriesInfo name="ED" value="262"/>
</reference> </reference>
<reference anchor="ICAO2015" target="https://standards.globalspec.co m/std/10026940/icao-9896"> <reference anchor="ICAO2015" target="https://standards.globalspec.co m/std/10026940/icao-9896">
<front> <front>
<title>Manual on the Aeronautical Telecommunication Network (ATN) using Internet Protocol Suite (IPS) Standards and Protocols, Doc 9896 <title>Manual on the Aeronautical Telecommunication Network (ATN) using Internet Protocol Suite (IPS) Standards and Protocol
</title> </title>
<author> <author>
<organization>International Civil Aviation Organization (ICAO)</organization> <organization>International Civil Aviation Organization (ICAO)</organization>
</author> </author>
<date year="2015" month="January"/> <date year="2015" month="January"/>
</front> </front>
<seriesInfo name="ICAO" value="9896"/>
</reference> </reference>
<reference anchor="RTCA2019" target="https://www.rtca.org/products/d o-379/"> <reference anchor="RTCA2019" target="https://standards.globalspec.co m/std/14224450/rtca-do-379">
<front> <front>
<title>Internet Protocol Suite Profiles, DO-379 <title>Internet Protocol Suite Profiles</title>
</title>
<author> <author>
<organization>Radio Technical Commission for Aeronautics (RTCA)</organization> <organization>Radio Technical Commission for Aeronautics (RTCA)</organization>
</author> </author>
<date year="2019" month="September"/> <date year="2019" month="September"/>
</front> </front>
<seriesInfo name="RTCA" value="DO-379"/>
</reference> </reference>
<reference anchor="SCH2016"> <!--REF1--> <reference anchor="SCH2016" target="">
<front> <front>
<title>Measurement of the L-band Air-to-Ground Channel for Posit <title>Measurement of the l-band air-to-ground channel for posit
ioning Applications ioning applications</title>
</title>
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<title>CRYSTALS-KYBER - Algorithm Specification and Supp orting Documentation (version 3.02)</title> <title>CRYSTALS-KYBER - Algorithm Specification and Supp orting Documentation (version 3.02)</title>
<author initials="R." surname="Avanzi"/> <author initials="R." surname="Avanzi"/>
<author initials="J." surname="Bos"/> <author initials="J." surname="Bos"/>
<author initials="L." surname="Ducas"/> <author initials="L." surname="Ducas"/>
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ence.I-D.ietf-raw-technologies.xml"/> o include the editor role -->
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rg/doc/html/draft-ietf-raw-technologies-06">
<front>
<title>Reliable and Available Wireless Technologies</title>
<author fullname="Pascal Thubert" initials="P." surname="Thubert" role="edit
or">
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<author fullname="Dave Cavalcanti" initials="D." surname="Cavalcanti">
<organization>Intel Corporation</organization>
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<author fullname="Corinna Schmitt" initials="C." surname="Schmitt">
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</front>
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</reference>
<xi:include href="http://xml2rfc.tools.ietf.org/public/rfc/bibxml3/refer <!-- [I-D.ietf-raw-use-cases] IESG state IESG Evaluation::AD Followup. Formatted
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<!-- RAW use cases --> long way to include the editor role -->
<reference anchor="I-D.ietf-raw-use-cases" target="https://datatracker.ietf.or
g/doc/html/draft-ietf-raw-use-cases-08">
<front>
<title>RAW Use-Cases</title>
<author fullname="Carlos J. Bernardos" initials="C. J." surname="Bernardos"
role="editor">
<organization>Universidad Carlos III de Madrid</organization>
</author>
<author fullname="Georgios Z. Papadopoulos" initials="G. Z." surname="Papado
poulos">
<organization>IMT Atlantique</organization>
</author>
<author fullname="Pascal Thubert" initials="P." surname="Thubert">
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ence.I-D.haindl-lisp-gb-atn.xml"/> <xi:include href="https://datatracker.ietf.org/doc/bibxml3/reference.I-D
<!-- Ground-Based LISP for the Aeronautical Telecommunications Network, .haindl-lisp-gb-atn.xml"/>
Work in Progress, Internet-Draft, draft-haindl-lisp-gb-atn-06 -->
<xi:include href="http://xml2rfc.tools.ietf.org/public/rfc/bibxml3/refer <!-- [I-D.ietf-rtgwg-atn-bgp] IESG state I-D Exists; formatted the long way to i
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<!-- A Simple BGP-based Mobile Routing System for the Aeronautical Telec <reference anchor="I-D.ietf-rtgwg-atn-bgp" target="https://datatracker.ietf.org/
ommunications Network --> doc/html/draft-ietf-rtgwg-atn-bgp-19">
<front>
<title>A Simple BGP-based Mobile Routing System for the Aeronautical Telecom
munications Network</title>
<author fullname="Fred Templin" initials="F." surname="Templin" role="editor
">
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</author>
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</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-rtgwg-atn-bgp-19"/>
</reference>
<xi:include href="http://xml2rfc.tools.ietf.org/public/rfc/bibxml3/refer <!-- [I-D.ietf-lisp-rfc6830bis] Published as RFC 9300 -->
ence.I-D.ietf-lisp-rfc6830bis.xml"/> <xi:include
<!-- The Locator/ID Separation Protocol (LISP) --> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.93
00.xml"/>
<xi:include href="http://xml2rfc.tools.ietf.org/public/rfc/bibxml3/refer <!-- [I-D.ietf-lisp-rfc6833bis] Published as RFC 9301 -->
ence.I-D.ietf-lisp-rfc6833bis.xml"/> <xi:include
<!-- Locator/ID Separation Protocol (LISP) Control-Plane --> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.93
01.xml"/>
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<!--<xi:include href="http://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference
.I-D.ietf-ipsecme-g-ikev2.xml"/>-->
</references> </references>
<section anchor="appendix" title="Selected Information from DO-350A"> <section anchor="appendix" title="Selected Information from DO-350A">
<t> This appendix includes the continuity, availability, and integrity <t> This appendix includes the continuity, availability, and integrity
requirements applicable for LDACS defined in <xref target="DO350A"/> . </t> requirements applicable for LDACS defined in <xref target="DO350A"/> . </t>
<t> <t>
The following terms are used here: The following terms are used here:
</t><dl spacing='compact'> </t><dl spacing='compact' indent='10'>
<dt>CPDLC</dt><dd> <dt>CPDLC:</dt><dd>
Controller Pilot Data Link Communication Controller-Pilot Data Link Communications
</dd> </dd>
<dt>DT</dt><dd> <dt>DT:</dt><dd>
Delivery Time (nominal) value for RSP Delivery Time (nominal) value for RSP
</dd> </dd>
<dt>ET</dt><dd> <dt>ET:</dt><dd>
Expiration Time value for RCP Expiration Time value for RCP
</dd> </dd>
<dt>FH</dt><dd> <dt>FH:</dt><dd>
Flight Hour Flight Hour
</dd> </dd>
<dt>MA</dt><dd> <dt>MA:</dt><dd>
Monitoring and Alerting criteria Monitoring and Alerting criteria
</dd> </dd>
<dt>OT</dt><dd> <dt>OT:</dt><dd>
Overdue Delivery Time value for RSP Overdue Delivery Time value for RSP
</dd> </dd>
<dt>RCP</dt><dd> <dt>RCP:</dt><dd>
Required Communication Performance Required Communication Performance
</dd> </dd>
<dt>RSP</dt><dd> <dt>RSP:</dt><dd>
Required Surveillance Performance Required Surveillance Performance
</dd> </dd>
<dt>TT</dt><dd> <dt>TT:</dt><dd>
Transaction Time (nominal) value for RCP Transaction Time (nominal) value for RCP
</dd> </dd>
</dl><t> </dl><t>
</t> </t>
<table anchor="tab_one"><name>CPDLC Requirements for RCP 130</name> <table anchor="tab_one"><name>CPDLC Requirements for RCP 130</name>
<thead> <thead>
<tr> <tr>
<th align='center'> </th> <th align='center'> </th>
<th align='center'>RCP 130</th> <th align='center'>RCP 130</th>
skipping to change at line 1781 skipping to change at line 1789
<td align='center'>1E-5 per FH</td> <td align='center'>1E-5 per FH</td>
<td align='center'>1E-5 per FH</td> <td align='center'>1E-5 per FH</td>
</tr> </tr>
</tbody> </tbody>
</table> </table>
<t> <t>
RCP Monitoring and Alerting Criteria in case of CPDLC: RCP Monitoring and Alerting Criteria in case of CPDLC:
</t><dl spacing='compact'> </t><dl spacing='compact'>
<dt>-</dt><dd> <dt>MA-1:</dt><dd>The system shall be capable of detecting failures and con
MA-1: The system shall be capable of detecting failures and configurati figuration changes that would cause the communication service to no longer meet
on changes that would cause the communication service no longer meet the RCP spe the RCP specification for the intended use.</dd>
cification for the intended use.</dd> <dt>MA-2:</dt><dd>When the communication service can no longer meet the RCP
<dt>-</dt><dd> specification for the intended function, the flight crew and/or the controller
MA-2: When the communication service can no longer meet the RCP specifi shall take appropriate action.
cation for the intended function, the flight crew and/or the controller shall ta
ke appropriate action.
</dd> </dd>
</dl><t> </dl><t>
</t> </t>
<table anchor="tab_three"><name>ADS-C Requirements</name> <table anchor="tab_three"><name>ADS-C Requirements</name>
<thead> <thead>
<tr> <tr>
<th align='center'> </th> <th align='center'> </th>
<th align='center'>RSP 160</th> <th align='center'>RSP 160</th>
<th align='center'>RSP 160</th> <th align='center'>RSP 160</th>
skipping to change at line 1854 skipping to change at line 1860
<td align='center'>1E-5 per FH</td> <td align='center'>1E-5 per FH</td>
<td align='center'>1E-5 per FH</td> <td align='center'>1E-5 per FH</td>
</tr> </tr>
</tbody> </tbody>
</table> </table>
<t> <t>
RCP Monitoring and Alerting Criteria: RCP Monitoring and Alerting Criteria:
</t><dl spacing='compact'> </t><dl spacing='compact'>
<dt>- </dt><dd> <dt>MA-1:</dt><dd>The system shall be capable of detecting failures and
MA-1: The system shall be capable of detecting failures and configur configuration changes that would cause the ADS-C service to no longer meet the R
ation changes that would cause the ADS-C service no longer meet the RSP specific SP specification for the intended function.</dd>
ation for the intended function.</dd> <dt>MA-2:</dt><dd>When the ADS-C service can no longer meet the RSP spec
<dt>-</dt><dd> ification for the intended function, the flight crew and/or the controller shall
MA-2: When the ADS-C service can no longer meet the RSP specificatio take appropriate action.
n for the intended function, the flight crew and/or the controller shall take ap
propriate action.
</dd> </dd>
</dl><t> </dl><t>
</t> </t>
</section> </section>
<section anchor='Acknowledgements' numbered="false"><name>Acknowledgemen
ts</name>
<t>
Thanks to all contributors to the development of LDACS and
ICAO Project Team Terrestrial (PT-T), as well as to all in the R
AW Working Group for deep
discussions and feedback.
</t>
<t>
Thanks to <contact fullname="Klaus-Peter Hauf"/>, <contact
fullname="Bart Van Den Einden"/>, and <contact
fullname="Pierluigi Fantappie"/> for their comments on this docu
ment.
</t>
<t>
Thanks to the Chair of Network Security for input and to the Res
earch
Institute CODE for their comments and improvements.
</t>
<t>
Thanks to the colleagues of the Research Institute CODE at the
UniBwM, who are working on the AMIUS project funded under the Ba
varian
Aerospace Program by the Bavarian State Ministry of Economics,
Regional Development and Energy with the GA
ROB-2-3410.20-04-11-15/HAMI-2109-0015, for fruitful discussions
on aeronautical communications and relevant security
incentives for the target market.
</t>
<t>
Thanks to SBA Research
Vienna for continuous discussions on security infrastructure
issues in quickly developing markets such as the air space and
potential economic spillovers to used technologies and protocols.
</t>
<t>
Thanks to the Aeronautical Communications group at the
Institute of Communications and Navigation of the German
Aerospace Center (DLR). With that, the authors would like to
explicitly thank <contact fullname="Miguel Angel
Bellido-Manganell"/> and <contact fullname="Lukas Marcel
Schalk"/> for their thorough feedback.
</t>
</section>
</back> </back>
</rfc> </rfc>
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