Aerospace and Electronic Systems Magazine November 2017 - 22

Feature Article:

DOI. No. 10.1109/MAES.2017.160282

Datalink Security in the L-Band Digital Aeronautical
Communications System (LDACS) for Air Traffic
Management
A. Bilzhause, B. Belgacem, University of Passau, Germany
M. Mostafa, T. Gräupl, German Aerospace Center (DLR), Wessling, Germany

INTRODUCTION
Today's very high-frequency (VHF) voice-based air-ground
communication system for tactical aircraft guidance is suffering from the VHF band's increasing saturation in high-density
areas [1]. The air-ground1 communication infrastructure is
therefore undergoing modernization to ensure the sustainable
growth of the European air transportation system in the coming
decades [2], [3]. One major goal of this effort is the introduction of computerized air traffic management applications and
new digital communication links between aircraft and ground
systems.
Air traffic management communication is therefore transitioning from analog voice communication to digital data communication. Digital networks are already used for air traffic
management to a limited extent. The most notable one is the digital Aircraft Communications Addressing and Reporting System
(ACARS) introduced in 1978, which uses very high-frequency
(VHF), or L-band2 satellite channels. In 2001, the European organization for the safety of air navigation (EUROCONTROL)
launched the LINK2000+ program to migrate air traffic management applications then running on top of ACARS to the open
systems interconnection (OSI) protocol stack on top of the VHF

The ground-ground communication infrastructure is outside the
scope of this paper.
The satellite L-band goes from 1,545 to 1,656.5 MHz.

Authors' current addresses: A. Bilzhause, B. Belgacem,
University of Passau, Institute of IT-Security and Security
Law, Innstrasse 43, 94032 Passau, Germany, E-mail: (ab@sec.
uni-passau.de). M. Mostafa, T. Gräupl, Deutsches Zentrum für
Luft- und Raumfahrt e.V. (DLR), Institute of Communications
and Navigation, Münchner Str. 20, Oberpfaffenhofen, 82234
Wessling, Germany. The research leading to these results has
been partially funded by the LUFO IV research program of the
Federal Republic of Germany in the ICONAV project.
Manuscript received December 30, 2016, revised July 12, 2017,
and ready for publication August 31, 2017.
Review handled by K. Kramer.
0885/8985/17/$26.00 © 2017 IEEE
22

Digital Link Mode 2 datalink3. However, this OSI protocol implementation is now considered obsolete, and VHF Digital Link
Mode 2 suffers from operational problems [4]. The Single European Sky Air Traffic Management Research (SESAR) program
will therefore migrate the air traffic management communication
infrastructure to a more sustainable technological basis. Broadband digital datalink technologies for aeronautical communication are therefore under development and will be integrated in
an Internet protocol (IP)-based aeronautical telecommunications
internetwork, called the future communications infrastructure
(FCI). The datalink technologies under development are the Iris
satellite link [5], the short-range terrestrial AeroMACS datalink
for airport communications [6], and the terrestrial long-range Lband4 digital aeronautical communications system (LDACS) [7]
that is the focus of this article.
Security and safety are strongly interrelated in aviation, according to Ben Mahmoud et al. [8]: Cybersecurity is therefore an
important aspect of the air-ground communication infrastructure.
The first aeronautical network introduced, ACARS, originally had
no security functions. Then, the Airlines Electronic Engineering
Committee developed a standard called ACARS Message Security
to provide end-to-end application layer security on top of the existing infrastructure [9]. ACARS Message Security is based on the
security specification of the OSI aeronautical telecommunications
network, which employs context management middleware for authenticated key establishment [10]. The established keys may then
be used by other air traffic management applications without further key exchanges [11]. Context management has been ported not
only to ACARS but also to the IP-based aeronautical telecommunications network under development (the FCI) [12]. In addition to
application-layer security, the FCI specifies the use of Mobile Internet Protocol version 6 (IPv6) with IP Security (IPSec) [13] and
Internet Key Exchange version 2 [14] in the network layer. In the
datalink layer, the current datalinks used by ACARS and the OSI
aeronautical telecommunications network (VHF and HF channels,

The term "datalink" is used in the civil aviation community to
refer to digital communication technologies for air-ground communication related to the safety and regularity of the flight [8].
The aeronautical L-band goes from 960 to 1,164 MHz.

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NOVEMBER 2017

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