International Civil Aviation Organization ACP- WGN/6
18 June 2006
AERONAUTICAL COMMUNICATIONS PANEL (ACP)
WORKING GROUP N (Networking) Sixth meeting
Brussels, Belgium; 3-7 July 2006
Agenda Item : 5 5: Air-ground applications
and 6 6: Ground-ground applications
(Presented by the Secretary)
Applications in the ATN/OSI and the ATN/IPS
1.1 Upper layer communications are defined in Annex 10 as follows.
Upper layers (UL) communications service. A term pertaining to the session, presentation and application
layers of the OSI reference model.
1.2 In Doc 9705, sub-volume 4, upper layer communications are referred
126.96.36.199 The UL specification supports all current ATN applications except
the ATS Message Application. This specification is designed to optimise the use of
communications bandwidth, and consequently restricts the functionality available
from the OSI Session and Presentation layers.
188.8.131.52 The ATN requirements are addressed for Session Layer (Layer 5),
Presentation Layer (Layer 6), and a part of the Application Layer (Layer 7) of the
OSI reference model. Figure 4.1-1 shows a conceptual view of the scope of the UL
communications service. The remaining part of the Application Layer is the province
of the individual ATN applications (i.e. the ADS, CM, CPDLC and FIS (ATIS)
specifications for air-ground applications, and the ICC (AIDC) specifications for
Scope of UL
Figure 4.1-1. Conceptual view of the scope of
the UL Communications Service
2. Scope of the upper layer communications.
2.1 Although the text of 184.108.40.206 is not specific, it is assumed that the ATN
requirements for the upper layer communications services which are addressed in
sub-volume 4 of Doc. 9705 include layer 5, layer 6 and part of layer 7 of the ATN
SARPs and detailed technical specifications. The remaining part of the application
layer (7), is named Application Entity, which is currently defined in Annex 10 as:
Application entity (AE). Part of an application process that is concerned with communication within the OSI
environment. The aspects of an application process that need to be taken into account for the purposes of
OSI are represented by one or more AEs.
2.2 This definition is not clear since it does not clarify which part of an
application process (or the application layer) is concerned with the application itself
and which part is concerned with communications. The second sentence in this
definition seems rather a note to the definition that forming part of the definition.
2.3 Figure 3.1 (Conceptual model for the ATN) refers to the application
process as not being part of the SARPs. However, it is assumed that the application
process is part of layer 7 (Application layer)
2.3 The following diagram shows a comparison of the various layers of
the ATN/OSI and the ATN/IPS, using the OSI layered model.
CM Context Management
ADS-C Automatic Dependent Surveillance (Contract)
FIS Flight infomrmtion service
CPDLC Controller to pilot datalink communications
ICC/AIDC Inter-centre communications/ATS interfacility
APPLICATION PROCESS APPLICATION PROCESS
A/G: CM, ADS-C, FIS, A/G: CM, ADS-C, FIS,
Application CPDLC CPDLC
Entity (AE) G/G: CM, ICC/AIDC G/G: CM, ICC/AIDC
Upper layer communications service
Layer 6 Layer 7
Internet communications service
ISO/IEC 8073 (TP4) Layer 4 IETF/RFC 793 (TCP)
and Transport Transfer Control Protocol
ISO/IEC .... (CLTP) layer IETF/RFC 768 (UDP)
User Datagram Protocol
ISO/IEC 8473 (CLNP) Network IETF/RFC 2460 (Ipv6)
layer Internet Protocol (v6)
3. Application layer in the Internet Protocol Suite
3.1 The application layer is the top layer of the Internet protocol suite.
The Internet suite does not further subdivide the application layer, although some of
the Internet application layer protocols do contain some internal sub-layering. The
application layer of the Internet suite combines the functions of the top three layers
Session, Presentation and, Application -- of the OSI reference model.
3.2 The application process generates (or receives) data (application).
The application layer prepares this data to be transmitted over the ATN (through
TCP/IP or UDP/IP in the ATN/IPS). The various methods for message transfer are as
FTP SNMPv3 DNS
Doc 9705 G-G Applications
ICMPv6 BGP-4 MPLS 802.X … others
Network Access Links
3.3 For applications, (AIDC, AMHS, CPDLC, FIS and ADS-C), the current
specifications in Doc. 9705 are a combination of the material contained in the upper
layer communications (Doc. 9705, sub-volume 4) and the material contained in the
ground-ground communications on (Doc. 9705, sub-volume 3) (Part of the
application layer is incorporated in the upper layer communications). This material
needs to be replaced with application layer material, contained in the relevant RFC’s
for either FTP, SNMPv3, DNS and others, as required.
3.4 AIDC, as specified in Doc. 9705 (and to be updated with the new material
from OPLINKP) can continue to be used in ATN/OSI systems or, on a temporary basis,
in ATN implementations using TCP/IPv4 but making use of the OSI upper layers
communications. However, the latter type of legacy implementation should be
discouraged, in particular for new ATN systems based on IPS only.
3.4 The structure of the applications over the ATN/IPS needs to be developed as
A P P L I C A T I O N P R O C E S S E S
AIDC AMHS CPDLC ADS FIS VoIP
A P P L I C A T I O N L A Y E R
FTP SNMPv3 DNS VoIP
TRANSPORT LAYER TCP/IP TRANSPORT LAYER UDP
NETWORK LAYER Ipv6
4. Action proposed:
To re-structure material on ATN/IPS applications along the lines necessary for an
efficient ATN/IPS implementation, making use of already existing IPS standards.