ACP - WGN06-WPxx
AERONAUTICAL COMMUNICATIONS PANEL (ACP)
WORKING GROUP N – NETWORKING
6th MEETING – BRUSSELS, BELGIUM, 3 – 7 July 2006
AFTN AIDC
over
ATN ICS or IPS
Prepared by AEROTHAI
Summary
This paper proposes an alternative to implementation of the ATN AIDC Application
as defined in ICAO Doc 9705. The alternative is to adapt the AFTN AIDC application
to be block oriented so that it may run over the ATN OSI-based Internet
Communications Service or the Internet Protocol Suite.
ACP - WGN06-WPxx
1. Introduction
The ATS Interfacility Data Communications (AIDC) application exchanges information
between ATS Units (ATSUs) for support of critical Air Traffic Control (ATC) functions
including:

Notification of flights approaching a Flight Information Region (FIR) boundary,

Coordination of boundary conditions and

Transfer of control and communications authority.
2. AIDC Variants in the Asia/Pacific Region
There are two variants of AIDC defined for the Asia/Pacific Region.
a) AFTN-based AIDC Protocol
The latest version 2.0 as documented in the Asia/Pacific Regional Interface
Control Document (ICD) for ATS Interfacility Data Communications (AIDC),
Version 2.0 – September 2003
b) ATN-based AIDC Protocol
This variant is under development based on Edition 3 of ICAO Doc 9705. It is not
yet submitted for approval by Bangkok ICAO Regional Office
3. Key Differences in the AIDC Variants in the Asia/Pacific Region
3.1 Control Logic
Control Logic is the rules governing the sequencing of messaging. The control logic for
AFTN AIDC is in the ATC Application and is depicted in Figure 1.
The control logic for ATN AIDC is in the Control Function of the Application Entity and is
depicted in Figure 2.
ACP - WGN06-WPxx
Figure 1 – AFTN AIDC Control Logic
Figure 2 – ATN AIDC Control Logic
ACP - WGN06-WPxx
3.2 Message Format and Encoding
AFTN AIDC messages are defined and encoded using standard AFTN text encoding while
ATN AIDC messages have a distinct abstract syntax (ASN.1) and PER encoding rules.
Figure 3 depicts the AFTN environment and Figure 4 depicts the ATN AIDC environment.
AIDC
App
AIDC
App
Text
Messages
Text
Messages
AFTN
Service
AFTN
Service
AFTN
Switch
AFTN
Switch
AFTN
Switch
Aeronautical Fixed
Telecommunication
Network
(AFTN)
Figure 3 - AFTN AIDC Architecture
AIDC
App
CF
ASN.1
Defined
Messages
AIDC
App
AIDC
ASE
CF
AIDC
ASE
ACSE
ACSE
FB Pres
FB Session
TP4
CLNP
FB Pres
FB Session
TP4
CLNP
ATN
RTR
ATN
RTR
ATN
RTR
Aeronautical
TelecommunicationS
Network
(ATN)
Figure 4 – ATN AIDC Architecture
ASN.1
Defined
Messages
ACP - WGN06-WPxx
4. Current progress in the development of AIDC
At the present, OPLINK panel has amended relevant information regarding AIDC at the
OPLINKP1 meeting on September 2005. The new architecture of AIDC has not been
incorporated in the ATN AIDC material in the technical manual.
5. Proposed Architecture – AFTN AIDC over ATN ICS
Rather than implement the ATN AIDC Upper Layer Architecture, an AFTN AIDC-like
architecture could be used. The concept is basically to run AFTN AIDC over the OSI Internet
Communications Service (over TP4/CLNP). Figure 5 depicts this environment.
Text
Messages
AIDC
App
AIDC
App
TP4
CLNP
TP4
CLNP
Text
Messages
ATN
RTR
ATN
RTR
ATN
RTR
Aeronautical
TelecommunicationS
Network
(ATN)
Figure 5 - AFTN AIDC over ATN ICS
The AIDC application in this case would be block oriented i.e. from the Transport Layer
perspective it would look like an OSI upper layer application. The advantage of this approach
is that it could readily operate in an IPS environment using RFC 1006. Thus if the
Asia/Pacific region were to eventually migrate to an IPS or dual IPS/OSI infrastructure the
application would be isolated from change.
5. Recommendation
The working group is invited to comment on the proposed AIDC approach.