Published on Australian Maritime Safety Authority (

Global maritime distress and safety system

The global maritime distress and safety system (GMDSS) connects you to coast stations and vessels via satellite and radio communications when you're out at sea.

Radios have been used to save lives at sea since 1899 and included the manual transmission of morse code and radiotelephone.

With evolution of digital technologies and satellite communication, the GMDSS was introduced in 1992 by the International Maritime Organization (IMO). The system transformed the way vessels and coast stations communicated in the maritime environment.

Critically, the GMDSS simplified the way vessels communicated a distress alert, improving the maritime search and rescue (SAR) system internationally. It also provided a unified capability for shore authorities to provide maritime safety information (MSI) in the form of navigation warnings, meteorological warnings and forecasts.

The GMDSS is supported by the International Cospas-Sarsat Programme, recognized mobile satellite service providers (including Inmarsat and Iridium) and digital selective calling (DSC) on the medium-, high- and very-high frequency (MF, HF and VHF) bands. This enables a distress alert to be transmitted and received automatically over both short and long distances.

The concept of GMDSS is that ashore authorities, as well as ships within the immediate vicinity of a vessel in distress, will be rapidly alerted to a distress incident and provide assistance as required under the International Convention for the Safety of Life at Sea (SOLAS Convention).

SOLAS convention

The SOLAS convention is a set of international regulations and standards governing all operational aspects of merchant ships. The convention has been endorsed by all major maritime nations which operate through the IMO.

All ships over 300 gross tonnage on international voyages are subject to the SOLAS convention and must comply with the carriage requirements of the GMDSS. The equipment carriage requirements will be determined by the area in which a vessel is operating within otherwise known as sea areas.

Australia’s GMDSS services

Australia is declared sea area A3. While there may be other governments establishing HF facilities in the Indian and Pacific Ocean areas, Australia aims to cover the Australian search and rescue region with its own stations.

AMSA provide for Australia’s GMDSS requirements through:

HF digital selective calling  

GMDSS HF radio services are provided by the AMSA HF DSC network, with sites positioned in Wiluna, Western Australia and Charleville, Queensland. The network provides continuous monitoring of the DSC distress frequencies and conducts follow on communications via radiotelephony or narrowband direct printing (NBDP).

The network has the capability to make broadcasts for search and rescue purposes and these will normally be preceded by a DSC announcement.

HF test call service

Mariners’ can perform radiocommunication checks when required by contacting VICTOR INDIA CHARLIE (VIC). This service supports DSC and radiotelephone.

Test call procedure for HF radiotelephone

When establishing routine communications by HF radiotelephone for the purposes of a test call request, listen on the calling frequency (4 125, 6 215, 8 291, 12 290 or 16 420 kHz) for any other traffic, and if vacant, the call should be made in the following manner:

Await a response on the calling frequency, repeat if necessary after two minutes, and if no response is received, move to another calling frequency and repeat the procedure.

For example, to establish routine communications for the purposes of a test call request to VIC:


THIS IS [vessel call sign x 2]



Pending operational availability, VIC will respond confirming receipt of the test call.

Test call procedure for HF digital selective calling

The test call service for HF DSC is an automated service.

To initiate a test call to the VIC shore station(s) on your HF DSC radio, choose ‘test call’, ensure you are communicating with shore station ID (MMSI) 005030001, and press ‘call’. If the test call was received by the shore station, it will be acknowledged.

Note: Please refer to your radio operation manual for specific procedures to follow for conducting a test call via DSC.

If no response is observed within 5 minutes try again on another DSC channel, or use another station in the GMDSS.

Related information

Last updated: 9 October 2023