DSC and ATIS

VHF Marine Band radios, protocol, radio communication theory, practical advice; AIS; DSC; MMSI; EPIRB.
jimh
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DSC and ATIS

Postby jimh » Fri Apr 20, 2018 10:08 am

Digital selective calling (DSC) is a global standard used by stations in the VHF Marine Band and on other maritime bands to implement ship identification and direct station-to-station calling. The automatic transmitter identification system (ATIS) is a regional system used in Europe ONLY on inland waterways as a method of vessel radio transmitter identification. As DSC is more familiar to boaters in the USA, it will not be described in detail here. ATIS is generally unknown in the USA, so a brief description of it will be given.

Perhaps the most basic information about ATIS is to not confuse it with AIS, the automatic identification system used globally and mandatory on large commercial ships.

ATIS is a identification system in which the VHF voice transmitter automatically appends a short digital burst of data to every voice transmission made by the radio. When the operator releases the PTT button, the transmitter continues to transmit (on the same voice channel) for slightly more than a quarter-second, switches to audio frequency shift modulation, and sends the identity of the vessel in a digital encoding. In the event of an extremely long transmission, the ATIS data must be sent at least once every five minutes. (The specifications require the transmitter to stop transmitting if the PTT is held for more than five minutes. )

The vessel identity sent by ATIS is NOT the global MMSI identity, but a separate regional European inland waterway identity, administered by a local authority in The Netherlands. The ATIS identity is derived from the ship station call sign of the vessel. The ship station call sign is then used to create a 10-digit ATIS identity. The ATIS identity is composed as follows:
  1. the first character is always a 9
  2. a three-digit MID encodes the maritime identification digits of the country of license of the vessel station
  3. the next two characters encode the second letter of the vessel callsign, with A as 01, B as 02, and so on
  4. the next four digits are the four numerals of the call sign
For example, a vessel from The Netherlands with ship station license call sign PC8075 would take the ATIS identity 9244038075, as follows:
  1. 9 as required by the method
  2. 244, the MID for The Netherlands, from the ITU callsign allocation of the prefix "PC" to The Netherlands; this establishes the first letter of the vessel call sign
  3. 03 for "C", the second letter in the call sign,
  4. 8075 from the four numeric characters of the original call sign digits

The technical details of the ATIS system, such as the encoding methods, modulation methods, and testing methods, are given in a document ETSI EN 300 698-1, Electromagnetic compatibility and Radio spectrum Matters (ERM); Radio telephone transmitters and receivers for the maritime mobile service operating in the VHF bands used on inland waterways; Part 1: Technical characteristics and methods of measurement. This standard is available for free download from

http://www.etsi.org/deliver/etsi_en/300600_300699/30069801/01.04.01_60/en_30069801v010401p.pdf

In today's global marketplace, many newer models of VHF Marine Band radios provide for an option to change the radio configuration to operate according to the ATIS protocol. This allows the manufacturer to make one radio design and hardware that can be sold across all major global markets, in various version. Typically a country-specific model of a radio must be ordered to get the ATIS feature. Radios sold in the USA market might not provide any ATIS features. The ATIS features are usually enable by selecting a different band plan setting, and available band plans tend to vary with the radio model being sold in a particular region. For example, the ICOM M605 radio is sold with five regional variations, each having different options for band plans:
  • USA
  • UK
  • European
  • German
  • Dutch
The band plan variations are:
  • USA
  • INT
  • CAN
  • DSC
  • ATIS
Band plan options vary according to which country model is purchased. In the M605, for example, the USA version only offers three band plans: USA, CAN (Canada), and INT (International). The ATIS band plan option is only available on the M605 if you buy the Dutch or German models.

From what I can tell, consumer grade ship station ATIS radios only encode the ATIS data on transmit. I do not believe the radios provide a decoding of the ATIS data they receive from other stations' transmissions. My inference is perhaps the waterway regulatory authorities monitor the radio traffic with receivers that can decode and display the vessel identity transmitted by ATIS.

ATIS radios are required to be used on the inland waterways of:
  • Austria
  • Belgium
  • Bulgaria
  • Croatia
  • Czech Republic
  • France
  • Germany
  • Hungary
  • Luxemburg
  • Moldova
  • The Netherlands
  • Poland
  • Romania
  • Slovakia
  • Switzerland
  • Serbia
  • Montenegro

On the inland waterways of the above countries, use of DSC radio methods is typically prohibited. In Germany, DSC may be used in certain inland areas that are near to coastal waters; the German country-variation of the M605 radio seems to have a special DSC band plan option provided.