In this document, the following definitions being used:
Administration of network address domains
A network address domain represents a finite set of values that can be assigned to a network address field used to delineate an address domain. For each network address domain, the choice of values relies upon addressing rules stemming from the SARPs and from this document.
The administration of a network address domain comprises the following operations:
Definition of sub-rules, the scope of which is limited to the boundary of the network address domain (these sub-rules are local matters outside the scope of this document, they shall be consistent with domain’s rules) ;
Identification of addressable network elements, integrated in the communication infrastructure and belonging to the administered address domain ;
Choice of appropriate values in compliance with the domain rules and assignment of these values to the relevant address fields of these network elements.
ATN NSAP Address
An ATN NSAP address is a 20-octet string used to uniquely identify and locate a given NSAP (i.e. a network service user) within the context of the ATN.
Network Entity Title (NET)
An ATN NET is a 20-octet string used to uniquely identify and locate a network layer entity of an ATN system (router or end system), and thus, in networking terms, is used to identify the system itself. Thanks to the global nature of the ATN inter-network addressing plan defined in [ICAO_9705] chapter 5.4, a system’s NET can be used to locate it anywhere within the ATN.
The syntax of an ATN NET is equivalent to that of an ATN NSAP address. It differs from the NSAP addresses assigned to the same system only in the last octet, i.e. the network selector (N-SEL) field value.
Routing Domain and Routing Domain Confederation Identifier
Each Routing Domain (RD) and Routing Domain Confederation (RDC) whose BIS(s) implement the IDRP protocol shall have an unambiguous identifier.
An RDI is an identifier the syntax of which is equivalent to the one of a NSAP or of a NSAP prefix. This means that RDIs are octet strings of up to 20 octets, and which are assigned statically according with [ISO_8348/2].
An RDI uniquely identifies a routing domain or a confederation, but does not necessarily convey any information about its policies or the identity of its members. Its main purpose is to allow the routers to determine, during IDRP connection establishment, whether the adjacent routers are members of the same Routing Domain and/or of the same Routing Domain Confederation.
Note that an RDI is a name and not an address. Therefore it conveys no location information about an RD or RDC. Conventionally, the RDI for a Routing Domain may be assigned using the same NSAP Address Prefix as used for the NSAP Addresses within the RD. An RDI for an RDC is assigned relative to an NSAP Address Prefix assigned to the Addressing Authority that assigns the RDI, but otherwise need have no relationship to the RDI’s assigned to its member RDs.
ATN Island RDC
The ground ATN Internet shall consist of one or more ATN Island RDCs. Each ATN Island shall comprise one or more ATN RDs forming a single Island RDC. An ATN Island RDC shall not contain any ATN Mobile RDs. ATN Island RDCs comply with the same naming and addressing rules than RDCs.
ATN Island backbone RDCs
A global ATN backbone shall comprise at least one ATN RD from each ATN Island, interconnected either directly or indirectly via other members of the global ATN backbone. Within each ATN Island, those ATN RDs that are members of the global ATN backbone should form a single RDC, which is referred to as the ATN Island backbone RDC. An ATN Island backbone RDC, when present, shall be nested within an ATN Island RDC.
The Figure 1 below illustrates these concepts.
In practice, the LINK 2000+ topology will be a simplified implementation of the ATN goal architecture. Air/Ground communications using VDL Mode 2 will be provided by Service Providers (i.e. ARINC and SITA) who will effectively form the ATN Island Backbone for the single ATN Island that comprises the LINK 2000+ domain.
Figure 1 : Example ATN Island Routing Domain Confederation Structure
Home domain
Aircraft for which inter-island communications are required shall have a “Home” domain, which is a Routing Domain in an ATN island. This “home” does not need to be in either the ATN Island through which the aircraft is currently reachable, or in the ATN Island with which communication is required. The role of the “Home” domain is to advertise a default route to all the aircraft belonging to an airline, or the General Aviation aircraft of a given country of registration. This default route is advertised to the ATN Global Backbone in line with the routing policies specified in [ICAO_9705] section 5.3.7. “Home” domains comply with the same naming and addressing rules as RDs.
There is no provision for the “Home Domain” in the LINK 2000+ topology as this concept only applies when multiple ATN Islands are interconnected.
ATN Application
An ATN Application provides application users with the communication services required by a particular operational task. These services are for example retrieval of aircraft generated data for ADS, management of pilot/controller message exchange for CPDLC or retrieval of ground generated flight information for DFIS.
Address Domain
An (ATN) Address Domain is a set of address formats and values administered by a single address authority. Under the ISO plan, any address authority may define sub-domains within its own domain, and delegate authority within those sub-domains.
Addressing Authority
An (ATN) Addressing Authority defines formats and/or values of (ATN) addresses within its jurisdiction (i.e. an ATN Addressing Domain).
Data Link Service
A Data Link Service is an operational task provided to final users requiring a communication task. The communication service required by the Data Link Service may be provided by an ATN Application.
ICAO Ground Facility Designations (described in [ICAO_7910]) are 4-letter codes used to identify aerodromes and aeronautical facilities around the world. The code starts by dividing the world into a series of regions, and allocating each region a letter. Most regions contain several countries, while some regions are considered large enough to have a letter allocated to a single country. The second letter then indicates the country within the region, while the third and fourth letters are then used to identify the particular facility within the country. There are four characters added to the indicator to determine the destination agency at the location.
Callsigns and Flight Ids
The current model of Air Traffic Control identifies aircraft by their Callsign (e.g. Speedbird 123) and which is synonymous with their Flight ID (e.g. BAW123). Both are recorded on an aircraft’s Flight Plan, and this model remains unchanged with the introduction of data link.
For commercial operators, the link between Flight ID and an aircraft is dynamic and often only lasts for a short time (i.e. the duration of a single flight). However, for other operators (e.g. General Aviation), the Flight ID is often fixed and corresponds to the Aircraft Registration Number. The system shall be able to cope with both transient and permanent relationships between the Flight ID and an aircraft.
Aircraft Registration Identifiers
The Aircraft Registration Identifier (a.k.a Tail Number) is a fixed identifier for an aircraft and is used by ACARS to identify the destination for uplink messages and the source of downlink messages.
ICAO 24-bit Aircraft Address
The ICAO 24-bit Aircraft Address is also a fixed identifier for an aircraft and was originally developed as a unique SSR code for Mode S. It is used by the ATN as a permanent identifier for an aircraft. The combination of Flight ID and ICAO 24-bit aircraft address is used to uniquely identify the aircraft operating a given Flight.
