In the context of aeronautical air-ground mobile data communications, the project is concerned with the development of network functions which enable interworking between legacy ATN/OSI and future ATN/IPS networks.
The context for the design of the Interworking Functions is Airtel’s existing ATN/OSI code base.
The objectives of the Interworking in the ATN study are as follows:
- To specify aeronautical network interworking functions and implement a prototype,
- To provide a concept of verification of the interworking functions to support the future overall verification and validation of the integrated communication system,
- To verify the defined interworking functions according to the defined concept.
The focus of the project is the implementation in software of a prototype of the ICAO IPS DSI function. The IPS DSI (defined in ICAO Doc 9896) provides interoperability between legacy ATN Air Traffic Control applications (designed around ATN/OSI) and future IPv6 networks. The IPS DSI implements a mapping of ATN/OSI primitives and protocols to IPv6 protocols and data structures.
In addition to the software implementation, the second achievement of the project was the conception, development and implementation of an ATN Interworking Demonstrator, using an ATS Function (CPDLC), to validate the ATN/IPS Function in an End-User environment. This Demonstrator was an Mobile IPv6 Test Bed.
The network functionality that is addressed represents a key enabler of the future European operational concept for Air Traffic Management (ATM), as specified by the SESAR programme. The project therefore contributes to the development of the next generation of European ATM infrastructure, which has been identified by the European Commission as a major driver of the European economy.
The IPS DSI permits legacy air-ground aeronautical applications, which operate over the existing ATN/OSI network, to operate unmodified over future IPv6-based aeronautical networks. The principal applications concerned are those employed in Air Traffic Control. The IPS DSI approach permits the substantial investment already made in ATC applications for ATN/OSI to be preserved and exploited further when IP-based aeronautical networks are deployed.
Airtel’s implementation is closely integrated with the company’s base of operational ATN/OSI software, thus ensuring that users of systems based on Airtel’s ATN/OSI code can deploy IPv6-based capabilities at an early stage.
Migration from the existing ATN/OSI to ICAO’s IPv6 standard (ATN/IPS) is facilitated by the approach of retaining the existing ATN applications and providing an interface to IPS which preserves (as far as possible) the applications’ existing interface to the network.
This interface is defined as the Dialogue Service Interface (DSI). This means that a new software function is required to adapt the legacy ATN applications to the IPS stack (to TCP/UDP in fact). This is illustrated in the following diagram (taken from ICAO Doc. 9896, “Manual for the ATN using IPS Standards and Protocols”), where the IPS DS is referred to as “OSI/IPS Convergence”.
Figure 1 ATN/IPS Protocol Archtecture
The ATN Interworking Functions to be provided for the purposes of testing the aeronautical data link system is called the IPv6 Inter-working Function or IPS DS.
In the transition to ATN/IPS, the protocols below the DSI are replaced by the IP protocol suite. The upper applications and services (ASEs, CM, and CPDLC) remain the same with the small exception of the network address format which is IPv6 instead of OSI.
The project delivered an implementation of the connection-oriented ATN/IPS software implementing the DSI interface and the ATN/IPS ULCS services below. The implementation is based on the ICAO ATN/IPS standards, Manual for the ATN using IPS Standards and Protocols (ATN/IPS SARPs), ICAO Doc 9896, Ed. 1.
Figure 3 ATN/IPS software architecture
A demonstration platform was delivered specifically tailored for validation of the Interworking Functions. The Demonstrator employs Airtel data link validation tools, which are in use in various test and demonstration environments in the ATM industry. The Airtel validation tools provide facilities for simulating aeronautical data link systems and end systems. The Demonstrator implements a mobile IPv6 Test Bed, which is the type of IPv6 network the ATN/IPS function is foreseen to be deployed on.
Figure 4 ATN/IPS Mobile IPv6 Test Bed