Aeronautical
Telecommunications
Services
Presented by Philip Clinch
on 27 September 2000
at ATN 2000
Facing up to the ATN
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The airlines established SITA (the International
Organization for Aeronautical Telecommunications)
to provide an international data network in 1948, just
as the International Civil Aviation Organization
began writing its convention Annex 10 standardizing
“Aeronautical Telecommunications”.
SITA now has to respond to ICAO’s latest addition to
Annex 10, the ATN standard which specifies a new
way of providing the terrestrial and air-ground data
network services we already provide.
Evolution of Air Transport
Data Communications
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Up to 1990, the telecoms industry had not developed
data network standards so SITA and the airlines
developed and used airline industry standards.
From 1990, SITA began implementing the telecoms
industry standards: X.25, Internet Protocol, Frame
Relay, Asynchronous Transfer Mode.
SITA has implemented integrated digital voice and
data service over Frame Relay and more recently
also over IP.
SITA core network evolution
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SITA has network access points in 220 countries,
supporting 160,000 customer connections.
The airlines have used SITA’s telecoms industry
standard services to introduce new systems using
generic interfaces, and today in particular Web
based systems using IP.
Airlines systems would only use an ATN Internet
interface to networks also used by ATS providers so
The number of airline systems using an ATN
interface is not expected to justify SITA deploying
ATN routers in the core network.
ATS use of generic networks
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Many ATS providers operate X.25 data networks that
transport radar data and AIS messages.
ATS communications are increasingly using generic
telecoms services:
– The FAA Telecommunications Infrastructure (FTI) initiative
seeks to replace the FAA’s leased lines with a Frame Relay
and ATM backbone.
– The Eurocontrol CFMU is seeking a regional IP service to
enable the Enhanced Tactical Flow Management System.
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As these ATS communications will not use the ATN
Internet, SITA can address them with the current
generic network.
ATN Specific Services
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The ATN standard specifies the following services:
ATS Message Handling Service (AMHS)
– AMHS is not an application, but rather a messaging service
based on the X.400 standard.
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ATS Interfacility Data Communications (AIDC)
– AIDC is the only terrestrial application designed to directly
use the ATN Internet. AIDC is the exchange of Air Traffic
Control information for active flights between FDPS’s,
called On-Line Data Interchange (OLDI) in Europe.
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ATS Data Link Applications
– CPDLC, ADS, CMA
Which ATS ground systems will
use the ATN Internet?
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ATS Message Handling Service (AMHS)
– As AMHS has its own addressing scheme, AMHS systems
can communicate via X.25 networks and do not require ATN
Internet routers. This makes it difficult to develop a
business case for deploying ATN routers to support AMHS.
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ATS Interfacility Data Communications (AIDC)
– As AIDC is only used between FDPS’s, a transition from
current FDPS interchange protocols such as OLDI to ATN
would generate only a limited number of terrestrial ATN
Internet terminals.
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FDPS’s that implement ATN Data Link applications
are also likely to use it for AIDC.
Aircraft use of the
ATN Internet
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The aircraft data link service has evolved more
slowly than the terrestrial services because of the
need to upgrade avionics.
Aircraft still use the ACARS link specified around
1980 for the transport of text messages.
The ATN Internet design covers the interconnection
of air-ground and terrestrial networks and this now
seems likely to be its primary function.
CPDLC usage in Europe and the USA requires better
performance than ACARS can provide and is driving
the implementation of the ATN internet.
SITA ATN Implementation
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As the primary use of the ATN Internet will be for
aircraft data link, the SITA ATN implementation is
focussed on the AIRCOM service.
SITA will at the end of 2000 begin deploying new
VHF ground stations to provide ICAO VDL Mode 2
service supporting ATN Internet communications.
The SITA deployment of ATN routers will be tailored
to meet needs of airline and ATS customers.
SITA is also implementing air-ground IP service but
aircraft are only expected to use it for passenger
services and file transfers.
Conclusion
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As most airline and ATS ground systems are using
the generic telecoms protocols, the terrestrial use of
the ATN Internet seems likely to be very limited.
Only aircraft data link applications can justify the
use of the specialised ATN Internet protocol, and
this should justify its use between the ground
systems that host these applications.
The ATN Internet needs to be implemented in aircraft
systems quickly to avoid AOC data link applications
migrating from ACARS to the planned IP networks,
which would undermine the ATN business case.