Communications: directive radio wave systems and devices (e.g. – Air traffic control
Reexamination Certificate
2002-08-09
2004-01-13
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Air traffic control
C342S051000
Reexamination Certificate
active
06677888
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to aircraft to ground communications devices and methods, and in particular to a secure data link between an aircraft and the ground based on Aircraft Addressing and Reporting System (ACARS) technology.
BACKGROUND OF THE INVENTION
Aircraft Addressing and Reporting System (ACARS) data link is used by commercial airlines worldwide for their day to day operations. Civil Aviation Agencies use ACARS for air traffic control (ATC) over oceanic regions where radar coverage is not available. Automated position reports transmitted via ACARS permit air/traffic controllers to accurately monitor the position of aircraft. In addition, controllers can send Air Traffic Management (ATM) messages to the pilot to actively control aircraft movement. As such, ACARS has been a key contributor in reducing separation standards over the oceanic air space.
ACARS messages are transferred over open RF channels in human readable forms. Low cost, COTS equipment enables anyone to monitor and process ACARS messages. It is possible to determine aircraft type, condition, position, projected track, cargo content, and operational details of the flight by analyzing ACARS messages. Aircraft operators would like to protect this information to maintain competitive advantage, to ensure safety of flight and to reduce operational liability.
Normally, US military aircraft are required to comply with the air-traffic requirements while flying in the civil air space. Since ACARS is used for air traffic control in the South Pacific region, the US Air Force (USAF) has started to equip its air transport fleet with ACARS to satisfy civil aviation requirements. Availability of ACARS also offers additional benefit to the USAF because ACARS can be used for routine, unclassified communications, thereby preserving the capacity of military communication systems for high priority traffic. There is a long felt need for military operators to use the existing civilian ACARS system in a secure manner. If messages can be exchanged over ACARS in a secure fashion, ACARS data link will allow USAF to track its fleet in near-real time and exchange information with any aircraft worldwide, thereby improving its operational efficiency.
Some commercial airlines have implemented ad-hoc data encryption techniques for ACARS. These techniques use simple character substitution algorithms that may protect the information from a casual hacker, but a sophisticated attacker will be able to break the code in a short period of time with nominal computational resources. As such, airlines and the military desire to develop a strong information security solution for ACARS that is standards-based and uses cryptographic algorithms that have been validated by the industry.
Furthermore, at present, air traffic is controlled in a given airspace by voice communications between the pilot and the controller. With continuous increase in the number of flights around the world, radio frequencies used for air traffic control communications are nearing saturation. Channel congestion is affecting the reliability of voice communications and reducing safety of flight. The channel congestion problem is compounded by the fact that system capacity can not be readily increased by adding frequencies because spare frequencies are not available in several regions. Future Air Navigation Systems (FANS) committee of the International Civil Aviation Organization (ICAO) has identified digital communications over data link as the only solution to meet future demand for air traffic control communications. ICAO developed a set of standards, called the Aeronautical Telecommunications Network (ATN) to facilitate the implementation of this digital communication system. See, e.g., International Civil Aviation Organization,
CNS/ATM PACKAGE
-1
STANDARDS AND RECOMMENDED PRACTICES
(SARPs), ICAO (1997), document 9705, Montreal, Canada, which is incorporated herein by reference. Eurocontrol, other civil aviation organizations, and US Federal Aviation Administration (FAA) are in the process of migrating to ATN.
Current measures of information security will become obsolete with the paradigm shift from voice based air traffic control to automated air traffic management using data link. ICAO has determined that denial of service, masquerade, and modification of information are the primary safety threats to ATM. See, e.g., Adnams, Martin,
OVERALL SECURITY CONCEPT.
ATNP/VG-1 WP6-11, Halifax, Canada, Eurocontrol, (1996), which is incorporated herein by reference. ICAO developed the ATN security solution based on Public Key Infrastructure (PKI) to mitigate these threats. See, McParland, Thomas,
CNS/ATM PACKAGE
-
II STANDARDS AND RECOMMENDED PRACTICES
(
SARPS
),
SUB
-
VOLUME VIII—ATN SECURITY SERVICES
, Draft, Tokyo, Japan, ICAO, (2001),which is incorporated herein by reference. In addition, ICAO is planning to mandate a sunrise date after which all ATM systems communicating via data link will be required to implement the ATN security standards.
The ACARS aeronautical data communications protocol is character based. As such, special characters are reserved and used as protocol delimiters. This limits the type of data that can be transported over the ACARS network as the reserved characters can not be present in user data stream. ACARS defines some escape sequences and special encoding schemes to transmit bit-oriented user data over ACARS to ensure that the reserved characters are not contained within the payload user data. This encoding scheme increases the size of the payload. For bit-oriented data, the payload size is doubled after applying ACARS encoding algorithm. ACARS communications frequencies are nearing saturation. Therefore, doubling the payload significantly reduces the number of users that can be supported by ACARS network. Secure communications technology is being developed for ACARS which will allow users to encrypt user data before transmission over ACARS network. Unfortunately, the encryption algorithms are likely to convert the user data from characters to bits which then have to be encoded again into characters for use with the character-based ACARS protocol, thereby doubling the size of the payload. As the customers are charged by the number of bits sent over ACARS, the developing security solution will double the costs of communications.
SUMMARY OF THE INVENTION
With the increase in automation, airlines, military, and civil aviation organizations are relying on ACARS for air traffic and operational control. Unfortunately, automated information exchange between airborne and ground computers also increases the vulnerability of the system and may severely impact the safety of a flight or an air space.
The Secure ACARS solution of the invention protects the aeronautical information transfer end-to-end over the ACARS data link using proven, state-of-the-art, standard-based, cryptographic techniques.
This invention provides specific techniques to relieve ACARS frequency saturation using an unique encoding/decoding scheme combined with standard data compression algorithm. Additional solutions are provided to encrypt the ACARS protocol header without requiring any changes to the legacy ACARS equipment. The secure ACARS solutions of the invention satisfy customer needs, improve the safety and reliability of the ACARS system and extend the usability of ACARS by conserving RF resources.
The secure ACARS solution of the invention is based on the ICAO ATN security standards, which has been extended to cover data encryption. Therefore, systems and policies developed to provide ACARS security can be used for ATN. Thus, the ACARS security solution of the invention protects investment in existing ACARS while satisfying known information security needs of both commercial and military users.
This invention proposes to modify ACARS data flow process to add compression/decompression capability. Although ACARS will benefit from any compression technique, use of DEFLATE algorithm (specified in Internet RFC 1951) and ITU-T standard V.42bis are recommend
Andrea Brian K
Honeywell International , Inc.
Rupnick Charles J.
Tarcza Thomas H.
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