An IPv6 Air/Ground Interface for the International Civil Aviation Organization (Use Case)

The International Civil Aviation Organization (ICAO) is building a worldwide IPv6-based Air Traffic Management (ATM) service known as the Aeronautical Telecommunications Network with Internet Protocol Services (ATN/IPS). Aircraft connect to the ATN/IPS via an Air/Ground (A/G) interface that provides a nexus for control and data message exchanges over all available underlying aviation wireless data links. Aircraft frequently have many data links and use them according to inbound and outbound traffic engineering profiles in a service known as multilink. As an aircraft travels, it's underlying aviation data link profile may change dynamically. For example, data links that are available in the ground domain may not be available at cruise altitudes, and terrestrial cellular services may not be available during trans-oceanic crossings. In still other cases, handoffs within the same access technology could result in readdressing. For these reasons, aircraft and the ATN/IPS must be able to accommodate mobility. The ATN/IPS provides an IPv6 /32 Mobility Service Prefix (MSP), and ICAO further assigns each aircraft a 24-bit Identification value that is unique among all civil aviation aircraft worldwide. From these two values, the aircaft constructs a /56 Mobile Network Prefix (MNP) that travels with the aircraft wherever it goes. For example, if the MSP is 2001:db8::/32 and the aircraft is assiged the Identification value 0x123456, the resulting MNP is 2001:db8:1234:5600::/56. Each aircraft registers its MNP in the ATN/IPS ground-domain mobility service over its active aviation data links. Since many aviation data links have very low-end performance profiles (e.g., 32Kbps) it is imperative that the MNP is conveyed in the fewest possible messages and with the smallest possible message sizes. This service is termed "prefix registration" (as opposed to "prefix delegation") since the aircraft already knows its MNP and is simply asking for it to be registered in the ATN/IPS routing system. Following prefix registration, the aircraft sends IPv6 data messages over the A/G interface and undelying data links according to its traffic engineering profile. The aircraft keeps the number of control messages to a minimum, since the ground domain is responsible for any keepalive messaging on behalf of the aircraft. In this way, reducing contol message overhead on aviation data links presents the greatest possible capacity for carrying actual data. While the ground domain ATN/IPS network will provide a mobility service, the details of the service need not be exposed to the aircraft. Instead, the aircraft simply operates its A/G interface in a manner that allows optimum data plane usage while providing the ground domain with only the necessary and sufficient control message signaling. This document therefore presents a use case for an aircraft A/G interface.

The terminology in the normative references applies; especially, the terms "link" and "interface" are the same as defined in the IPv6 and IPv6 Neighbor Discovery (ND) specifications. The following terms are defined for the purposes of this document: The global governing body for civil aviation standards. A command and control messaging service for coordinating safe aviation operations. A proposed worldwide IPv6-based network used to enable ATM services between aircraft and air traffic controllers. The ability of an aircraft to coordinate its available aviation data links through traffic engineering link selections. The ability of an aircraft to adapt to changes in its underlying aviation data link connectivity and availability.