Air-ground Router for ATM Safety Communication

Status date

In the framework of the Iris programme, the development of end-user satellite equipment on ground and on-board the aircraft will be conducted. This will require the development of test beds for interoperability testing, including functionalities not covered by the satellite communication standard.

In this context, one identified activity is the development of an air-ground router (AGR) for the ATM safety communication. The AGR is the point at which the satellite sub-network interfaces with the European Air Traffic Management Network (EATMN). Due to the safety-related nature of ATM communication traffic, specific design and architecture is required for the AGR when compared to commercial off-the-shelf products.

The main objective of the present project is to design, manufacture and test a prototype of an ATN/IPS air-ground router as the interface between EATMN and the ground earth station.

As the aircraft moves between the GESs, it obtains a new IP address valid within a new subnet supported by the new AGR. During the transition phase MN within the aircraft is no longer reachable for the ATM applications under its old IP address, therefore without specific measures taken, the existing transport sessions will break until the new IP address is assigned and registered. Therefore, the key issue in the AGR project is extending the period of an interruption-free IP connectivity between moving aircraft and the ATC/AOC ground-based units.

 GES switchovers in case of GES failures must be handled in the same sense as handovers and will be addressed within the AGR project as safety communications service interruption over longer periods cannot be tolerated.


Currently there is no commercial IPv6-based air-ground router on the market that would be suitable for future satellite-based links for safety communications foreseen in SESAR. Therefore, the development of the AGR within this task enables first time testing of end-to-end ATC and AOC applications running over an IPv6 network and the satellite-based communication link.

The basic functionalities of the air-ground router are classification, forwarding and scheduling of the IP packets. Moreover, the air-ground router must cope with demanding requirements for a satellite based mobile communication system for safety-related services such as supporting seamless aircraft handover between coverage areas of Ground Earth Stations (GES), and providing uninterrupted IP connectivity in case of GES switch-over upon GES failure.
As the legacy IP standards are developed without considering specific characteristics of mobile links, special considerations must be taken into account to overcome the typically long Round Trip Time (RTT) of the satellite communication system with different possible satellite constellations (geostationary orbit or other).
The basic mobility concept supported by the AGR is based on IETF Mobile IPv6 (MIPv6). This standard allows each ordinary fixed ground node that implements IPv6 to reach the MIPv6-compatible Mobile Node (MN).
Sophisticated harmonization techniques between network and link layers must be in place for reduced handover latency and packet loss during handovers.
The air-ground router is a Quality of Service (QoS)-aware router. It supports the provision of QoS on an end-to-end basis using the DiffServ model allowing for different forwarding Per-Hop-Behaviour (PHB) for different classes for ATM data applications.
To dynamically exchange the routing information with other ATN/IPS entities, the AGR implements the BGP-4+ protocol utilizing TCP connections between involved entities.

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The project plan comprises 4 tasks as described below:
Task 1:
The main objective of this task is to capture the technical functional requirements necessary for the development of the ATN/IPS AGR based on the ICAO Doc 9896, COCRv2, as well as relevant deliverables of ARTES 10/Iris, ARTES 1, SJU projects 15.2.4 and 15.2.6.
ICAO Document 9896 specifies the standards for the Aeronautical telecommunication network based on IPv6. On the other hand IETF RFCs deliver the detailed standards for IPv6 protocol suite including mobility management. However, existing RFCs put no particular focus on satellite based communication and are even less concerned with ATM, therefore another objective of this task is to merge and harmonize requirements specified by ICAO and IETF. The output of the task 1 is the Technical Requirements Document (TRD) that serves as the input to task 2.
Task 2:
The objective of this task is to define the functional architecture of the ATN/IPS AGR based on the TRD along with related test/validation scenarios for the AGR. The main input to task 2 is the TRD. Task 2 provides two documents, Test Plan Document (TPD) and Functional Architecture Report (FAR). TPD is the input to task 3 and task 4. FAR is the input to task 3.
Task 3:
The main objective of this task is the development and testing of ATN/IPS software modules, fulfilling the identified functional architecture specified in task 2, and running on COTS hardware. All functional elements from FAR shall be covered. The inputs to task 3 are TPD and FAR. Task 3 generates the Software/Hardware Architecture Document (SHAD) and the Unit Test Results (UTR) documents.
Task 4:
The main objectives of this task are the completion of ATN/IPS AGR development from task 3 and the final software integration on the Linux platforms. The further output of this task is AGR User Manual, including detailed configuration and installation information. Input documents to task 4 are SHAD and UTR documents. Task 4 produces the final ATN/IPS AGR prototype and associated documentation.
The preliminary integration tests may lead to some refinements of the technical requirements (TRD) or even may lead to the adoption and implementation of new requirements, if necessary. 

Additional tasks have been conducted with the objective to add the network mobility (NEMO) functionality and verify NEMO support with the integrated air-ground router and mobility testing environment.

Current status
The activity is completed.
From the beginning of the AGR project onwards, a full set of deliverables has been produced, reviewed and accepted by ESA: 
  • Technical Requirements Document (TRD)
  • Test Plan Document (TPD)
  • Software/Hardware Architecture Document (SHAD) 
The AGR hardware has been configured, required software installed, and required features implemented, followed by the validation activities. AGR validation – checking the compliance of the AGR implementation with TRD – has been successfully closed. In the course of AGR development and validation activities further four deliverables have been produced, reviewed and accepted: 
  • Unit Test Results Document (UTR)
  • Integration Test Results Document (ITR)
  • Design Definition File Document (DDF)
  • User Manual (UM) 
The current AGR implementation allows for emulating the Interface between EATMN and SATCOM sub-network as well as supporting the harmonized L3 handover of MNs and the smooth switchover of GESs.
The AGR hardware/software will remain available for subsequent functional enhancements. Integrated in the Mobility Testing Environment for ATM (MTE), it is prepared to serve as a first run Interoperability Test Bed (ITB) in context of Iris programme activities.
Under ESA Contract Change Notice (CCN) to ESA Contract N0- 4000105488/12/NL/AD – called NEMO task – in 2013 the integration of the AGR with the MTE has been implemented.   Under above CCN, Network Mobility (NEMO) basic support has been implemented and tested within Integrated Mobility Testing Environment for ATM (IMTE), derived by combining the components produced within previous AGR/MTE tasks. IMTE (shown in the figure below) comprises more components that MTE, in particular additional NEMO-specific items (Mobile Router – MR, Mobile Network Node – MNN) have been added. 

Within the NEMO task, the following results have been achieved: 
  • NEMO-specific requirements (TRD-NEMO) have been defined and the test plan (TPD-NEMO) developed for validating these requirements in IMTE
  • Technical note (TN-NEMO) about using NEMO in the ATS and AOC environment has been produced
  • IMTE has been set-up and configured according to the previously defined parameters
  • IMTE Test Manager (TM) entity has been installed, providing remote access to other IMTE components
  • Validation of NEMO requirements has been successfully performed and documented (VRD-NEMO)
  • The duration of interruption and the number of lost packets have been measured during harmonised L2-L3 handover and GES switchover, indicating significant improvements when REIL is used, as developed within the AGR project
  • AGR ability of producing unicast RA messages has been demonstrated when modified radvd SW is used, as developed within the AGR project
  • TM ability to configure and control other IMTE components in complex test scenarios has been demonstrated
  • User manual (UM-NEMO) and SW user manual (SW_NEMO) have been produced