BP15, F- 91220 Bretigny/Orge Cedex

Since 1996, The Eurocontrol Experimental Centre (EEC) has been involved in R&D activities dealing with Internet Telephony technology for innovative Voice Communication System (AudioLAN project) and with Internet’s next generation protocol (IPv6 project) evaluation in the context of the Aeronautical Telecommunication Network. Today, COTS Internet Technology products are available to build aeronautical telecommunication mass-market based in an operational environment. After a description of the actual Aeronautical Telecommunication Network (ATN) status, this paper will undertake a technical discussion on an operational ATN based on Internet products, and will address benefits of such an approach for industrials and ATC community.

Keywords: Internet Technology, IPv6, ATN

In the early 1980's, the International Civil Aviation Organisation (ICAO) recognised the increasing limitations of the present air navigation systems and the need for improvements to take civil aviation into the 21^st century. ICAO established the Special Committee on Future Air Navigation Systems (FANS) with the task of studying, identifying, assessing new concepts and new technology, and making recommendations for the co-ordinated evolutionary development of air navigation for the next twenty-five years. From this, the ATN (Aeronautical Telecommunication Network) was specified in the ICAO Standards and Recommended Practices (SARPs). The ATN is a data communications inter-network that provides its users with a robust and reliable Air/Ground and Ground/Ground communications service.

The current ICAO standard for the Air Traffic data network is ATN/OSI; it is based on OSI protocols, with adaptations specific to aeronautical applications. At the time of developing the ATN Standards and Recommended Practices (SARPs) the Internet Protocol (IPv4) was not capable of providing the facilities for the ATN to meet its objectives and was not expected to become the protocol of the future.

For many years, the Internet community knew that IPv4 had many weaknesses that needed to be overcome. Only in the last few years, it has become necessary that these problems be solved quickly. The Internet Engineering Task Farce (IETF) established a working group to upgrade the Internet protocol, the IPNGWG (Internet Protocol Next Generation Working Group). ^[1] This working group has broadly specified a new version of the Internet Protocol, called IPv6 (IP version 6). At the moment it is not fully specified and standardised. However, there is strong interest in the Internet community for IPv6 with many experiments, developments of prototypes and integration tests for it to become a reliable and robust standard. Remembering that Internet development lifecycle is very fast, for example IP telephony took two years (1997) to become a commercial reality for the mass-market

The goal of this study is to provide an assessment of the adequacy of IPv6, and its ability to fulfil the requirements of aeronautical applications as set forth by ICAO documents such as the ATN/OSI SARPs. The interest of IPv6 for air applications is twofold:

• IPv6 is an industry-driven; emerging set of standards that are still being developed based on the needs of users and the actual implementation of new protocols and methods. Conversely, the ATN/OSI standards were completed before any implementation work was started.
• IPv6 are free, open standards and follow the technical evolution.

The Aeronautical Telecommunications Network (ATN) is a data communications inter-network that provides:

1. A common communications service for all Air Traffic Services Communications (ATSC) and Aeronautical Industry Service Communication (AINSC) applications that require either ground/ground or air-ground data communications services,
2. Integrates and uses existing communications networks and infrastructure wherever possible,
3. Provides a communications service, which meets the security and safety requirements of ATSC and AINSC applications, and
4. Accommodates the different grades of service required by each ATSC and AINSC application.

As the ATN is to provide a common infrastructure for ATC applications, the marginal cost for introducing a new application should be small and concentrated on the specific functions that it implements; as the communications infrastructure will already be there. Therefore, the ATN has been specified to meet the requirements of the Civil Aviation Community and is expected to give the following benefits:

• Use of the existing infrastructure
• High availability
• Mobile Communications
• Prioritised end-to-end
• Scalability
• Policy Based Routing
• Use of COTS Products
• Improved Communication

When a protocol was needed for the ATN, OSI was the considered as the only one that could meet most of the ATN requirements. However, after more than a decade the ATN based on OSI is now having difficulty meeting the ATN requirements in the following areas :

• Native Mobility
• Security
• Reliable Multicast
• Scalability
• Lack of COTS products

The Internet has established itself as a primary vehicle for a global system of electronic commerce, enabling a vast array of client/server and peer-to-peer computing applications. Although the Internet has been successful, and is expected to continue expanding at a rapid rate ^{(see table below)}, industry has just recently realised that the current version of its protocol (IPv4) has not advanced in comparison to computers and network applications that it supports. . In anticipation for the need to upgrade IP, the Internet Engineering Task Force (IETF) has produced a comprehensive set of specifications that define the next generation IP protocol known as "IPng" or " IPv6". Though IPv6 is based on much needed enhancements to the IPv4 standards, IPv6 is regarded as broad retool project to provide a much needed evolutionary re-architecting of today’s over stressed inter-networks. IPv6 is considered both as near term and long range concern for owners and service providers. On the one hand IPv6 products have already come on the market; and on the other hand, IPv6 will continue into the next decade as issues such as addressing performance, scalability, security, ease of configuration and network management are addressed.

The risk that the IETF considered when specifying IPv6 is the "second generation syndrome", which consists of adding everything users ask for at the expense of producing a slow, non-manageable, useless protocol. The question was then, which features from IPv4 were to be maintained, which were to be removed and which new are to be introduced.

1. Larger address space.
2. Autoconfiguration
3. QoS (Quality oft Service)/Priority
4. Security
5. Multicast and Anycast addresses.
6. Mobility
7. Policy based routing
8. Transition strategy from IPv4 to IPv6
9. Unify Intranets and the Internet.
10. Better use of LANs.
11. Support for Asynchronous Transfer Mode's Quality of Service.

Since July 1996, IPv6 has been making massive leaps from the implementation of a project to a standard. Though IPv6 is still in its infancy it is rapidly growing and will certainly become a mature and robust standard for the next millennium.

At the moment, IPv6 is not ready to be used in the ATN. However, this does not mean that work should not be done to include it in the ATN. Though the ATN is older with its use of the OSI protocol, it is not much more mature, and it certainly has had less enthusiasm and experimentations. It is, therefore, important that IPv6 is considered as the protocol for the ATN. IPv6 is coming and will offer, not only the advantages listed before but also the following:

• Linked with emerging technologies
• Large industrial investment
• COTS Products
• The IETF co-ordinates activity with other standards bodies (e.g. ATM Forum ^[4]).
• Industrial implementations
• Transition Mechanism
• Mobile Telephones
• CORBA
• Java/Jini

The EEC is involved in experimenting, evaluating and implementing Internet technologies with regard to the aeronautical environment, and is actively involved in the COIAS IPv6 project (European Commission, DGXIII). The EEC is a member of the COIAS consortium of which the other members are: University College of London, (UK), INRIA (FR), Thomson-csf Detexis (FR), British Telecom (UK), Secunet (G). ^[5]

The COIAS project aims at developing and demonstrating the new generation of Internet protocols based on IPv4 and IPv6 above ATM (Asynchronous Transfer Mode) and satellite. It will take into account the main features for the Information Society: performance, quality, mobility, reliable multicast and security, to be used in the ATC community.

It will use existing ATM and satellite technologies. Focusing on developing, implementing and evaluating IPv4/v6 software as proposed by the IETF standards on:

• Security (IPSEC)
• Mobility (Mobile IP)
• Integrated Services (IS)
• IPv6-over-ATM

At the EEC, a platform has been constructed to evaluate the following IPv6 features in relation to Air Traffic Control, Air Navigation and Passenger applications.

To evaluate these features the EEC has several applications that it is using to simulate the appropriate components in the ATC environment. The applications used are :

The EEC IPv6 platform has integrated addressing plan, routing, QoS (DiffServ) facilities. The security, mobility and reliable multicast features of IPv6 are currently being implemented.

When OSI was chosen for the ATN, it was the only network protocol at the time that could meet most of the ATN requirements. However, the problem with OSI is that within the commercial environment there is little interest for OSI, and therefore, minimal investment in OSI products. In fact, OSI has not fulfilled that expectation that it would replace TCP/IP as the new standard. This has meant that the aeronautical community has to assist in financing the development of ATN products, which has had the result that advancement in ATN products are relatively slow and that these products are not COTS products but bespoke.

Though IPv6 is still in its infancy the commercial sector is actively participating and investing in its development and evolution. Not only are networking companies interested in improving the Internet, but telecommunication companies, with regards to mobile communication, cable television networks, and satellite TV are also looking to the Internet to expand their markets. It is predicted that these markets will move closer together offering similar facilities but all using the Internet protocol. ^[6] IPv6 gives them, the potential to realise their ambitions.

With all this interest and activity in IPv6 it is important that it is not overlooked. There is a vast amount of commercial investment being made into IPv6, especially with its interface to other technologies, such as, satellite, ATM, mobile telephones, television, wireless LANs, Java, multicast, and mobility, that these technologies should not be ignored. It is essential that IPv6 be evaluated as it continues to evolve and standardise, for it, and all the technologies surrounding it, will bring benefits to the aeronautical community.

1. IPv6 Information Page (http://www.ipv6.org/)
2. ICAO ATNP Version 2.3 ATN SARPs (http://www.fans-is.com )
3. Matrix Information and Directory Service (www.mids.org)
4. ATM Forum (http://www.atmforum.com/)
5. COIAS Project (http://www.cs.ucl.ac.uk/staff/jon/coias/)
6. The Death of Distance - Frances Cairncros, Harvard Business School Press, ISBN0875848060 (http://www.hbsp.harvard.edu)