Home' RTCA Documents for Review : DO-262D Contents Appendix E
© RTCA, 2018
The aircraft avionics only send one ACARS message at a time, and then waits for
confirmation from the ground. The ATN/OSI protocol does define some Quality of
Service (QoS) mechanisms however these mechanisms are not used in practice. The
ADGW therefore does not arbitrate on priority of different ACARS and ATN/OSI
messages (i.e. first come first served). The ATN/IPS QoS mechanisms are yet to be
Security Gateway (Optional)
The Airborne Security Gateway (ASGW) implements an IPsec/IKE Virtual Private
Network (VPN) with peer Ground Security Gateway (GSGW). The VPN provides end-
to-end authenticity and integrity across the Inmarsat’s system. Encryption can also be
added to the VPN, subject to the requirements and constraints that may apply from
national security regulators. The ASGW is only used with the enhanced ACARS,
ATN/OSI and enhanced PS voice services and it is omitted if given AES is configured
to support just the standard ACARS and PS voice service.
Every SwiftBroadband modem provides a single circuit-switched voice channel using
an AMBE+2 voice codec. Furthermore, at least one voice channel using Voice over
IP (VoIP) technology is provided per AES. These two voice channels enable two
voice calls (telephone calls) for the flight deck.
In the standard PS voice service the VoIP facility is provided by a VoIP gateway in the
AES, which connects over SBB IPv4 service to a VoIP gateway on the ground. The
airborne VoIP gateway sets up a background priority PDP context at start-up for
signaling related to the priority VoIP call. A streaming context is set up on demand to
handle the voice sample stream.
For the enhanced PS voice service the airborne VoIP gateway connects through the
airborne security gateway to a security gateway and a VoIP gateway on the ground.
The VoIP signaling uses the background PDP context set up by the air security
gateway during the air-ground VPN setup. A secondary streaming context is set up
on demand to handle the voice sample stream.
Apart from the two voice channels for the flight deck, an AES may provide for
additional VoIP channels, which would typically be used outside the flight deck.
Data interface for ACARS and ATN/OSI is typically based on ARINC 429 standard.
Ethernet ports are typically used to interface IP data to the AES (including ATN/IPS).
Other formats such as AFDX or other are also possible.
An industry-standard interface between the AES and the flight deck audio system is
described in ARINC 781. The interface emulates, in broad terms, the speaker /
microphone / PTT interface of a VHF radio transceiver. Additional discrete lines
provide for visual and audible indication of incoming calls. Other interfaces are
Other interfaces to aircraft avionics may be required for the AES to receive information
such as aircraft speed, position and attitude, weight on wheels etc. Additional
functions like built-in testing, software loading etc. may be supported. These functions
may vary in different AES designs, and are not prescribed in this appendix.
The AES control function is responsible for internal AES management, including such
tasks as initializing and assigning modem resources, controlling high power amplifier
output power, controlling or directing antenna steering, self-test, fault isolation, etc.
The actual implementation of these functions is manufacturer-dependent. Tests for
the correct operation of such functions are inherent in the functional tests defined in
Section 2.4 of this appendix, therefore, the control function is not separately or
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