ACP WGN03- WP19
29 Apr 2004
AERONAUTICAL COMMUNICATIONS PANEL(ACP)
WORKING GROUP N (NETWORKING) – 3RD MEETING
Montréal (Canada), 19th May – 28th May 2004
Standards Discrepancy in CPDLC Version indication
Presented by EUROCONTROL
Summary
This paper highlights a discrepancy between ED-110 and Doc 9705 regarding valid
values of the ATN Application Version Number parameter.
Standards Discrepancy in CPDLC Version indication
Ref : CITRS/T19/DEL/D03
TABLE OF CONTENTS
1.
Introduction .....................................................................................................................................1
1.1
References ................................................................................................................................1
1.2
Abbreviations ............................................................................................................................1
2.
Problem Statement .........................................................................................................................1
3.
Conclusions ....................................................................................................................................2
4.
Appendix A – Extract from ED-110 ................................................................................................3
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Date: 29 Apr 2004
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Standards Discrepancy in CPDLC Version indication
Ref : CITRS/T19/DEL/D03
1.
INTRODUCTION
This paper highlights a discrepancy between the RTCA/EUROCAE Interoperability
Requirements document [2] and ICAO Doc 9705 regarding valid values of the ATN
Application "Version Number" parameter.
The interoperability requirements document [2] was jointly developed by RTCA SC-189 /
EUROCAE WG-53. It provides interoperability requirements standards for the initial
implementation of the Aeronautical Telecommunication Network (ATN), referred as ATN
Baseline 1, which support several Air Traffic services.
1.1
1.2
References
[1]
Manual of Technical Provisions for the Aeronautical Telecommunication Network
(ATN), ICAO Doc. 9705, Third Edition - 2002, Sub-Volume IV: Upper Layer
Communications Service.
[2]
EUROCAE ED-110 / RTCA DO-280 Interoperability Requirements for ATN
Baseline 1 (Interop ATN B1) (July 2002)
Abbreviations
AE
APDU
ASE
ATN
CM
COTS
CPDLC
PDU
2.
Application Entity
Application Protocol Data Unit
Application Service Element
Aeronautical Telecommunication Network
Context Management application (Doc 9705 chapter 2.1)
Commercial Off-The-Shelf
Controller-Pilot Data Link Communication application (Doc 9705
chapter 2.3)
Protocol Data Unit
PROBLEM STATEMENT
In developing interoperability specifications for CPDLC, the RTCA/EUROCAE working
group found it necessary to specify a subset of the CPDLC message elements specified
in ICAO Doc 9705 and Doc 4444 to support the initial services defined as "Baseline 1".
The ED-110 standard provides requirements for three slightly different subsets of the
CPDLC message set. A mechanism was required to convey the message set capabilities
between air and ground CPDLC ASEs. Ground systems can then use this information to
determine whether to offer the CPDLC service to an aircraft, while aircraft can use the
information to determine whether to expect CPDLC service provision from the ground
system.
The mechanism chosen by RTCA/EUROCAE was to make use of the application
information exchanged by the CM application to indicate which message subsets are
supported by air and ground CPDLC implementations. This has the advantage that no
changes are needed to the standard CPDLC protocol.
The CM Logon request and Logon response messages each contain a list of applications
supported by air and ground peers, together with the application version number, ATN
address and optional security parameters for each supported application.
In the CM Logon exchange, the application type is identified by an AEQualifier value
(strictly this should be "app-type" value, as AE Qualifier is used for other purposes in SubVolume IV extended addressing). Valid app-type values must lie in the range 0 to 255
and standard values are assigned in Sub-Volume IX (e.g. value "2" identifies CPDLC).
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Standards Discrepancy in CPDLC Version indication
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The VersionNumber field is an integer in the range 1 to 255. It is assumed in Doc 9705
(though not explicitly stated) that this field will contain the application version number as
specified in the relevant part of Sub-Volume II.
The CPDLC Technical Provisions (Doc 9705 section 2.3.2.1.1) state:
"The CPDLC-air-ASE and CPDLC-ground-ASE version numbers shall both be set to one
(basic CPDLC functionality) or two (CPDLC functionality supporting security)."
However, it is not clear whether this requirement also applies to the CPDLC version
numbers carried in the CM Logon.
The published RTCA/EUROCAE solution for communicating the supported message sets
is to split the CM VersionNumber into three components such that:
 The first decimal digit (hundreds) indicates the CPDLC ASE version number as
defined in CPDLC Technical Provisions (currently only 1 and 2 are defined).
 The second decimal digit (tens) indicates the dynamic operational capabilities.
 The third decimal digit (units) specifies the message subset.
There is thus a gap in the ATN standards. The CPDLC provisions only specify Versions
1 and 2 while the interoperability requirements specify Versions 110, 111, 112, 210, 211
and 212. There are no provisions in Doc 9705 describing how an implementation is
expected to format and interpret the CM VersionNumber.
One problem with the ED-110 structure is that it will not accommodate any future versions
of the CPDLC protocol that may be specified in future editions of Doc 9705.
It is believed that the ED-110 version number structure has not been widely implemented
by suppliers of ATN systems. Further, the LINK 2000+ programme in Europe has
decided not to adopt the ED-110 version number provisions in the initial services being
deployed.
3.
CONCLUSIONS
The Working Group is invited to consider the standardisation issue raised in this paper
and to develop an appropriate interoperable solution to the issue of CPDLC message
subset identification.
If the ACP working group endorses the RTCA/EUROCAE approach, then:
a)
the VersionNumber structure should be standardised in Doc 9705 and
b)
the link between CPDLC ASE version number and the VersionNumber
carried in CM exchanges should be made explicit.
If the ACP working group does not agree with the RTCA/EUROCAE approach, then:
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a)
an alternative solution is needed to the real-world problem of CPDLC
message subset identification, and
b)
a communiqué should be sent to RTCA/EUROCAE requesting the removal
of the non-standard version number values.
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4.
APPENDIX A – EXTRACT FROM ED-110
3.1.2.1.2.10 Application Version Number Support
The version number of the CPDLC application conveyed in the AP version number in the
CM-logon request/response compliant with this document is 110 or 210 (integer). This
indicates that:
 the CPDLC ASE is version 1 (the ‘1’10) or 2 (the '2'10), and
 the dynamic operational capabilities are version 1 (the 1‘1’0), and
 the P/OICS (e.g., message set) is version 0 (the 11‘0’).
Note 1: This document provides requirements for three CPDLC application versions.
Ground systems can use the version information to determine whether to offer the
CPDLC service to an aircraft. Aircraft can use the version information to determine
whether to expect CPDLC service.
Note 2: The use of the version number in this document is an interpretation of the SARPs
requirement that facilitates interoperability. However the “11x” was chosen to represent
the AE version 1 in the “hundreds” digit, dynamic operational capabilities in the “tens”
digit, and the “x” being the sub version of the baseline.
Note 3: In order to avoid overloading the current specification, this document and Annex
B will still refer to CPDLC version number 110, 111 and 112. Whenever "110", "111" or
"112" appears, it is meant "110 or 210", "111 or 211", "112 or 212" to take into account
the case CPDLC ASE version is 2.
3.1.2.1.2.10.1 When the airborne CPDLC application:
 supports the message elements indicated as mandatory, but
 does not support the message elements that are indicated as mandatory for
version 111 or 112
in tables M-4 and M-5 in section B.4.1 of Annex B of this document, it shall indicate that
the CPDLC version number is equal to the value “110” in the Logon Request parameter
Version Number of the CM-logon request.
3.1.2.1.2.10.2 When the airborne CPDLC application:
 supports the message elements indicated as mandatory, and
 supports the message elements that are indicated as mandatory in version 111 but
 does not support the message elements that are indicated as mandatory in version
112
in tables M-4 and M-5 in section B.4.1 of Annex B of this document, it shall indicate that
the CPDLC version number is equal to the value “111” in the Logon Request parameter
Version Number of the CM-logon request.
3.1.2.1.2.10.3 When the airborne CPDLC application:
 supports the message elements indicated as mandatory, and
 supports the message elements that are indicated as mandatory in version 111
and
 support the message elements that are indicated as mandatory in version 112
in tables M-4 and M-5 in section B.4.1 of Annex B of this document, it shall indicate that
the CPDLC version number is equal to the value “112” in the Logon Request parameter
Version Number of the CM-logon request.
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