An a-periodical service is a service where the transmission of data is triggered by specified events based on the data content e.g. a data field changes value by more than a specified threshold.

Amalgamation is the process by which tracks from co-operating systems are merged to form an 'amalgamated' track. It is used to smooth any possible differences between the tracks to allow the same amalgamated track information to be served to the users of both systems.

Service to distribute data from a source to all systems connected to the communications infrastructure. Broadcasting does not require the establishment of a session and allows sending of information to a large group of receivers.

List of all data items defined within a specific ASTERIX category describing the items by their reference, structure, size and units (where applicable).

Target for which the tracker has sufficient information to be sure that it is a track.

Unit of information seen by the application as a discrete entity by its contents. A Data Block contains one or more Record(s) containing data of the same category.

Composition of data items to serve a specific application or technology.

Physical implementation for the purpose of communication of a Data Item, it is associated with a unique Field Reference Number and is the smallest unit of transmitted information.

The smallest unit of information in each Data Category

A piece of information (e.g. the position of a target) directly derived from the radar information and transmitted without any intermediate processing.

An enhanced mode of SSR which permits the interrogation of all SSR equipped aircraft and the addressed interrogation of suitably equipped aircraft and two-way exchange of digital data between such aircraft and the interrogator.

A periodical service is a service where the information is transmitted at regular, user defined, intervals.

A radar synchronised service describes the distribution of tracks synchronised with the rotation of a specific radar.

A collection of Data Fields of the same category preceeded by a Field Specification field, signalling the presence/absence of the various Data Fields

An SDPS information service is uniquely identified by a service identification and is composed of a track element and a sensor element. A track element is characterised by the track selection (e.g. set of Mode-3/A codes, filtering in height, primary only, secondary only…), the track item selection (e.g. WGS-84 position, Time of Day…), the track transmission characteristics (e.g. synchronised on sensor, periodical, a-periodical event-triggered). A sensor element is characterised by the sensor selection, the sensor item selection, the sensor transmission characteristics.

After an interruption the transmission of datat for the related service is restarted.

A service suspension causes the temporary suspension of data transmission for the related service.

A service termination causes the transmission of data to cease and the service to be terminated.

Point to point connection between a user and an SDPS.

A vector describing the state of an object in terms of position co-ordinates, ground speed, course, acceleration and Mode-of-Flight.

Target for which the tracker has not yet sufficient information to confirm that it is a track.

Time sequence of state vectors of an object estimated by some real time filtering technique using surveillance data as input.

The mechanism for assigning Data Items to Data Fields, and containing all necessary information which needs to be standardised for the successful encoding and decoding of the messages.