Digital Selective Calling (DSC)

Back to:	CIRM Knowledge Base
Page completeness level:	Medium

Overview

DSC is intended to be used in the Medium Frequency (MF), High Frequency (HF) and Very High Frequency (VHF) bands of the Maritime Mobile Service (MMS), for distress, urgency and safety communication and general communications.

DSC is a technique that allows a radio operator to send a digital call, or 'Alert' to one or more selected radio stations. The main purpose of a DSC Alert is to warn the recipient that a voice transmission is about to be made that is of direct concern to them. A DSC Alert is generally followed by a radiotelephone voice transmission.

The advantages of sending a DSC Alert are that:

• In an emergency, a Distress Alert containing essential information can be sent quickly and simply.
• The Alert is repeatedly and rapidly transmitted in a digital format, (in the case of a VHF DSC, the Alert is sent five times within a few seconds on Channel 70). The information is transmitted digitally on a dedicated frequency, (Channel 70), and so is less susceptible to errors. Consequently the system virtually guarantees that someone within the A1 area will receive the Alert.
• Ultimately, a continuous listening watch on Channel 16 will no longer be essential as any message relevant to a station will be preceded by a DSC Alert.

DSC Classes

Equipment for generation, transmission and reception of DSC is designed according to the following equipment classes:

• Class A: includes all the facilities defined in annex 1 of ITU-R Recommendation M.493 and complies with the IMO GMDSS carriage requirements for MF/HF installations and/or VHF installations;
• Class B: provides minimum facilities for equipment on ships not required to use class A equipment and complies with the minimum IMO GMDSS carriage requirements for MF and/or VHF installations. This equipment provides for:
  • alerting, acknowledgement and relay facilities for distress purposes;
  • calling and acknowledgement for general communication purposes; and
  • calling in connection with semi-automatic/automatic services, as defined in ITU-R Recommendation M.493, annex 2, clause 3;
• Class D: provides minimum facilities for VHF DSC distress, urgency and safety as well as routine calling and reception as recommended by IMO MSC/Circ 803 for non-SOLAS vessels participating in the GMDSS;
• Class E: provides minimum facilities for MF and/or HF DSC distress, urgency and safety as well as routine calling and reception as recommended by IMO MSC/Circ 803 for non-SOLAS vessels participating in the GMDSS.
• Class H: handheld equipment intended to provide minimum facilities for VHF DSC distress, urgency and safety as well as routine calling and reception, not necessarily in full accordance with IMO GMDSS carriage requirements for VHF installations.
• Class M: Man overboard equipment intended to provide the facility to activate a Distress alarm on a predefined ship or for a predefined group of ships (closed loop) or all ships (open loop) in the vicinity. This equipment does not provide any voice capability and is not an IMO GMDSS carriage requirement.

Performance standards, testing standards & carriage requirement

• ITU-R Recommendation M.493-15 - Digital selective-calling system for use in the maritime mobile service
• ITU-R Recommendation M.541-9 - "Operational procedures for the use of digital selective-calling equipment in the maritime mobile service".
• ITU-R Recommendation M.689-2 - "International maritime VHF radiotelephone system with automatic facilities based on DSC signalling format".
• ITU-R Recommendation M.1082-1 - "International maritime MF/HF radiotelephone system with automatic facilities based on DSC signalling format".
• ETSI EN 300 338-1 - Technical characteristics and methods of measurement for equipment for generation, transmission and reception of Digital Selective Calling (DSC) in the maritime MF, MF/HF and/or VHF mobile service; Part 1: Common requirements
• ETSI EN 300 338-2 - Technical characteristics and methods of measurement for equipment for generation, transmission and reception of Digital Selective Calling (DSC) in the maritime MF, MF/HF and/or VHF mobile service; Part 2: Class A/B DSC
• ETSI EN 300 338-3 - Technical characteristics and methods of measurement for equipment for generation, transmission and reception of Digital Selective Calling (DSC) in the maritime MF, MF/HF and/or VHF mobile service; Part 3: Class D DSC
• ETSI EN 300 338-4 - Technical characteristics and methods of measurement for equipment for generation, transmission and reception of Digital Selective Calling (DSC) in the maritime MF, MF/HF and/or VHF mobile service; Part 4: Class E DSC
• ETSI EN 300 338-5 - Technical characteristics and methods of measurement for equipment for generation, transmission and reception of Digital Selective Calling (DSC) in the maritime MF, MF/HF and/or VHF mobile service; Part 5: Handheld VHF Class H DSC
• ETSI EN 300 338-6 - Technical characteristics and methods of measurement for equipment for generation, transmission and reception of Digital Selective Calling (DSC) in the maritime MF, MF/HF and/or VHF mobile service; Part 6: Class M DSC

Standards in Development

• ETSI EN 300 338-7 - Technical characteristics and methods of measurement for equipment for generation, transmission and reception of Digital Selective Calling (DSC) in the maritime MF, MF/HF and/or VHF mobile service; Part 7: Interfacing DSC radio equipment to Bridge Alert Management systems (BAM)
• ETSI EN 300 338-8 - Technical characteristics and methods of measurement for equipment for generation, transmission and reception of Digital Selective Calling (DSC) in the maritime MF, MF/HF and/or VHF mobile service; Part 8: Enabling DSC radio equipment with remote control capabilities

Typical system components

• Component 1
• Component 2...

Detailed requirements

The RF equipment shall be capable of operation on one or more of the following frequencies:

• For distress, urgency and safety purposes:
  • MF: 2 187,5 kHz;
  • HF: 4 207,5 kHz, 6 312 kHz, 8 414,5 kHz, 12 577 kHz and 16 804,5 kHz;
  • VHF: channel 70 (156,525 MHz).
• For routine call purposes:
  • Ship to ship MF: 2 177,0 kHz simplex;
  • Ship to coast station MF: 2 177,0 kHz Rx / 2 189,5 kHz Tx;
  • HF: within the band 4 MHz to 27,5 MHz (HF), see ITU-R Recommendation M.541-9, annex 5;
  • VHF: channel 70 (156,525 MHz).

Additionally the equipment may be capable of operation on frequencies from the following bands as permitted by the ITU Radio Regulations:

• 415 kHz to 526,5 kHz;
• 1 606,5 kHz to 4 000 kHz;
• 4 MHz to 27,5 MHz;
• 156 MHz to 174 MHz.

(Performance Standard)

Definitions
Term	Definition
Term 2	Defintion 2
Module A - Title
Section title	Para number	Requirement

See also

(Content)