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Introduction

EUROCONTROL is a pan-European, civil-military organisation established to support European aviation operations to improve safety, security, efficiency and effectiveness.

ASTERIX (All Purpose STructured Eurocontrol suRveillance Information EXchange) refers to a range of protocols for standardised information exchange between aviation systems. Category 240 (CAT-240) describes an open standard for the transmission of rotating radar video.

The ability to support ASTERIX CAT-240 allows customers to receive ‘raw’ radar data without requiring Witness tools or a Navtech-supplied client library.

The CAT-240 standard is a way of exchanging radar video between a source of data and one or more destinations.

For customers and integrators intending to use ASTERIX CAT-240, the documents assume a reasonable working knowledge of UDP network communication. They are targeted at technical teams, typically with software development skills, who are integrating the output from Witness into external systems.

Contents

Overview

Navtech radars now have the capability to produce FFT (video) output in one of two formats:

  • Navtech proprietary format (Colossus).

  • ASTERIX Category 240 (CAT-240).

Navtech Specification for ASTERIX CAT-240

The CAT-240 standard allows some level of flexibility, to allow the data format to be adapted to meet the requirements of a particular application.

The Navtech-specific implementation, including specific configuration and extensions, is documented here: ASTERIX CAT-240 protocol for video data.

Network Configuration for Output Formats

The default Navtech (Colossus) data output format is a TCP-based protocol, and each azimuth is sent as a single message. Client applications are required to connect to the radar’s IP address and Data Distribution port.

ASTERIX CAT-240 does not specify a transport protocol as part of the standard. Typically, CAT-240 data is provided over UDP. The Navtech implementation can either unicast FFT (video) data to a specific IP address and port or, if supported by the system’s network configuration, multicast to a group IP address.

For the CAT-240 protocol, each azimuth of FFT data may be sent as multiple messages (see Max Packet Size in the https://navtechradar.atlassian.net/wiki/spaces/PROD/pages/2410283009/ASTERIX+CAT-240#Data-Output-Settings below for more detail).

It is the client application’s responsibility to re-combine messages into a single azimuth.

Changing the Radar Output Format

The radar output can be switched between the Navtech (Colossus) format and CAT-240 format via the Vertex user interface.

Setting the output format is part of the radar operational configuration and can only be performed by an admin user.

Changing the output format only takes effect once the radar has been rebooted.

To change the format to CAT-240:

  1. Log on as an admin user. Select System Configuration:

  2. Select the drop-down arrow in the Protocol field in the Data Output section:

  3. Select CAT-240 from the Protocol drop-down:

  4. You can then amend the parameters as desired (please refer to: https://navtechradar.atlassian.net/wiki/spaces/PROD/pages/2410283009/ASTERIX+CAT-240#Data-Output-Settings in the notes below for information regarding these settings) and click Apply:

  5. A confirmation message will be displayed. Select Commit Changes:

  6. A Data Applied Confirmation message will be displayed:

  7. You will then need to reboot the system for the Data Output changes to take affect:

  8. Click Reboot:

  9. Below is an example of the CAT-240 output:

Data Output Settings

IP Address: This is used in conjunction with the Sensor Port parameter and defines the endpoint that the UDP messages are sent to.

If the IP Address specified is a multicast address (that is, an IP address between 224.0.0.1 and 239.255.255.255) this will enable multicast sending of the CAT-240 data to that address.

Max Packet Size: This parameter specifies the maximum CAT-240 UDP packet size and is used to minimise potential problems of data loss when sending high-volume data over UDP.

Message datagrams larger than the Max Packet Size will be split into smaller messages, with no message exceeding the Max Packet Size (although they may be smaller).

The default setting of 1400 will alleviate the data loss problem on most networks. However, the client (receiving) application will need to re-assemble multiple packets into a single azimuth of data.

If the network configuration supports Jumbo Frames, the Max Packet Size may be set up to 9000 before packet loss may become a problem.

Larger values increase the risk of data loss.

More information about UDP packet loss and message splitting can be found here: https://navtechradar.atlassian.net/wiki/spaces/PROD/pages/2421260375/ASTERIX+CAT-240+protocol+for+video+data#Packet-fragmentation.

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