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Digital Selective Calling


DIGITAL SELECTIVE CALLING

Special Notices and Alerts

*** Mariner’s Safety Endangered When VHF Radio Distress Alerts by Digital Selective Calling (DSC) Lack Location and Identification Information

As the Coast Guard’s new marine radio network, Rescue 21, becomes operational throughout the U.S., rescue centers will have the ability to receive instant distress alerts from commonly used DSC-capable VHF marine radios; however, approximately 90% of VHF DSC distress alerts received by the Coast Guard do not contain position information, and approximately 60% do not contain a registered identity. The Coast Guard cannot effectively respond to a DSC distress alert sent from such a radio. As a result, search and rescue efforts may normally be suspended when:

no communications with the distressed vessel can be established; no further information or means of contacting the vessel can be obtained from other sources; and, no position information is known.

Please see the USCG Marine Safety Alert on this topic.

Instructions for interconnecting the GPS receiver or chart plotter to the VHF radio may be found in the installation manual for both devices. Also available:

• A water resistant trailer hitch connector (will open a new browser window), available from most auto parts stores, may provide a means for disconnecting and removing the radio when frequent removal is necessary. • A wiring guide (PDF; will open a new browser window) describing how popular GPS receivers and plotters can be properly interconnected to your VHF marine radio. You may also view this same wiring guide in an Excel spreadsheet. • NMEA’s DSC-VHF Check List. Ensure there is no RS-232 / RS-422 mismatch when interconnecting these devices.

Also, information MMSI is available. TESTING DSC

DSC-equipped radios purchased after March 2011 must have a test calling capability. Transmitting a test call (not a routine DSC call) to the identity 003669999 will trigger a reply from any USCG Rescue 21 station within range. If your radio does not have a test call capability, you can test it by sending a DSC call to another DSC-equipped radio.

The radio’s display will indicate if the GPS receiver has been properly connected.

*** DSC-Equipped Marine Radios Must Meet More Rigorous Technical Standards Beginning March 25, 2011

Beginning March 25th, 2011, the Federal Communications Commission will prohibit the manufacture, importation, sale and installation of fixed mounted (non-portable) digital selective calling (DSC) equipped marine radios that do not meet the requirements of International Telecommunications Union (ITU-R) Recommendation M.493-11 or higher, and in the case of Class D VHF DSC equipment only, International Electrotechnical Commission (IEC) International Standard 62238. Therefore, after March 25, 2011, radios built to RTCM Standard SC-101 can no longer be manufactured, imported, sold or installed; however, previously-installed radios meeting the older standard may continue to be used. See the USCG Special Notice.***

*** Special Notice Regarding U.S. Coast Guard MARINE SAFETY ALERT - AUTOMATIC CHANNEL SWITCHING ON DSC-EQUIPPED RADIOS

Certain models of Digital Selective Calling (DSC) equipped VHF maritime radios will automatically switch from a working channel to Channel 16 upon receipt of a DSC distress alert, distress alert acknowledgment and other DSC calls in which a channel number has been designated. A navigation safety hazard may consequently occur if the radio is being used to maintain a listening watch or to communicate on the designated bridge-to-bridge radiotelephone or vessel traffic services (VTS) monitoring channel. You may view updated information including a listing of manufacturers of radios believed to be affected by this Safety Alert. You may view the alert in PDF. (Note, this alert contains a link to an older, depricated Digital Selective Calling page. Please ignore this link.)

*** Manufacturer, Importation, Sale or Installation of RTCM SC101 Radios Prohibited On March 25, 2011

The Federal Communications Commission has prohibited the manufacturer, importation, sale or installation of non-portable DSC-equipped radios that do not meet either ITU-R Rec. M.493-11 or IEC 62238 Class D standards effective March 25, 2011 . This regulation effectively bans the sale of radios built to the RTCM SC101 standard on that date. A similar prohibition will apply to portable radios effective March 25, 2015 . See 47 CFR 80.225(a)(4).

About Digital Selective Calling

The U.S. Coast Guard offers VHF and MF/HF radiotelephone service to mariners as part of the Global Maritime Distress and Safety System. This service, called digital selective calling (DSC), allows mariners to instantly send an automatically formatted distress alert to the Coast Guard or other rescue authority anywhere in the world. Digital selective calling also allows mariners to initiate or receive distress, urgency, safety and routine radiotelephone calls to or from any similarly equipped vessel or shore station, without requiring either party to be near a radio loudspeaker. DSC acts like the dial and bell of a telephone, allowing you to "direct dial" and "ring" other radios, or allow others to "ring" you, without having to listen to a speaker. New VHF and HF radiotelephones have DSC capability. History

On February 1, 1999, the Safety of Life at Sea (SOLAS) Convention, a treaty document, required all passenger ships and most other ships 300 grt and larger on international voyages, including all cargo ships, to carry DSC- equipped radios. Ships were allowed to turn off their 2182 kHz radio listening watch on that date. The International Maritime Organization has postponed indefinitely plans to suspend this VHF watch on ships It had originally planned to suspend this watch on February 1, 2005.

Because of the safety problems that lack of communications interoperability would cause between SOLAS-regulated vessels (mostly cargo ships) and other vessels (recreational boaters, commercial fishing vessels, etc.), the Coast Guard petitioned the Federal Communications Commission in 1992 to require all marine radios made or sold in the U.S. have a DSC capability. The Coast Guard had also asked the Radio Technical Commission for Maritime Services (RTCM), a non-profit professional organization, to develop a standard which would allow incorporation of DSC in a marine radio without affecting the low-end market price of that radio. The FCC solicited comments on that petition in 1992 and 1993, and prepared a Notice of Proposed Rulemaking on that and other maritime radiocommunications matters in early 1994. The FCC requested comments concerning that rulemaking from May to November 1995 On 27 June 1997, the FCC adopted a Report and Order requiring radios type accepted on or after 17 June 1999 to include this minimum DSC capability. Recommendations On Digital Selective Calling (DSC) Test Calls To Coast Stations

The International Telecommunications Union Sector for Radiocommunications has indicated that excessive test calls on MF/HF DSC distress and safety frequencies are overloading the system to the point where interference to distress and safety calls has become a cause for concern.. To minimize possible interference, live testing on DSC distress and safety frequencies with coast stations should be limited to once a week as recommended by the International Maritime Organization

US Coast Guard Sea Implementation of Areas A1 (VHF)

Currently, the USCG is implementing GMDSS in Sea Area A1.One element of the USCG National Distress and Response System Modernization Project, is called "Rescue 21", which updates the USCG VHF distress system to include DSC capability & direction finding capabilities.

**The Coast Guard can't reliably receive VHF DSC distress calls where Rescue 21 has not been installed.

US Coast Guard Sea Implementation of Areas A2 (MF)

Many USCG Sectors operate MF DSC on a limited basis The US does has no plans to declare Sea Area A2.

US Coast Guard Sea Implementation of Areas A3 &A4 (HF)


*The stations have limited MF capability.

Interconnection to a GPS Receiver

All DSC-equipped radios, and most GPS receivers, have an NMEA 0183 two-wire data protocol That NMEA protocol allows any model of GPS to be successfully interconnected to any model of radio, regardless of manufacture Although NMEA has no standard for the type of cable or connector used, many if not most DSC and GPS receiver manufactures generally use ribbon cable with no connectors. These wires are simply connected between the radio and the GPS by twisting the wires (some people solder) and tape (some people use waterproof heat shrink tubing) Note also that NMEA 0183 and IEC 61162-1 data interfaces are identical.

**The Coast Guard urges, in the strongest terms possible, that you take the time to interconnect your GPS and DSC-equipped radio Doing so may save your life in a distress situation! Before interconnecting your radio & GPS consult the owner's manuals. Distress Relays

The single largest operational problem of the U.S. Coast Guard concerning DSC had been responding to the large number of MF/HF DSC distress relays being sent by ships ITU regulations require each relay to be individually acknowledged The Coast Guard treats each distress alert relay as if it were a separate distress Worse, certain radios insert the identity of a ship sending a relay, rather than relaying the identity of the ship in distress. The USCG requested that vessels not relay any DSC distress message which has already been acknowledged If you do relay a distress message, make sure the identity of the vessel in distress is correct, and send the relay to a USCG radio station using an identity such as 003669999, rather than sending it to all ships.

Since this problem was identified, radio operators have cooperated to reduce the number of relays transmitted Consequently, this is far less of a problem now. DSC problems and plans to correct them.

Continuing DSC problems include:

The biggest problem is the lack of follow-up voice comms after transmission of a DSC call, particularly a distress call Unnecessary and frequent alarms Distress alerts without accurate location information Distress alerts with unregistered MMSI identification Limited use of DSC for routine communications Inconsistent and illogical software menu defaults Alarms disrupting ongoing radiocommunications

In 2001 the International Telecommunications Union, in addressing these problems, began a major update to their DSC standard Rec ITU-R M.493 to address these problems. Changes were adopted in and published in early 2004. The Safety of Life at Sea Convention now requires radios be interconnected to electronic position fixing devices (e.g. GPS receivers) Radios meeting these new requirements should show significant improvement over earlier models, and many problems listed above should no longer occur Of course, new radios will be designed to be fully interoperable with older radios. IMO Flowcharts

The International Maritime Organization Communications and Search & Rescue Subcommittee released COMSAR Circular 45 of 04 February 2009, which includes simplified flowcharts on the actions a person on a ship should perform on receipt of a distress alert using DSC-equipped radios The documents is in Acrobat PDF format.

DSC Forum

You may sign up for the free GMDSS email list and participate in the discussion forum sponsored by Densham and Associates, Australia. The Navigation Center nor the U.S. Coast Guard endorses this site; it is mentioned for the reference purposes only. Classes of Digital Selective Calling

The DSC protocol is defined by ITU-R Recommendation M.493 (series), available from the International Telecommunications Union in Geneva, Switzerland DSC operation is defined by ITU-R Recommendation M.541 (series). Click the Classes hyperlinks in blue to go to that Class. A B D E RTCM SC101h ITU-R-Rec:M.825-3

ITU-R-Rec:M.821 Class A:

Distress call All-ships call Individual station call Semi-automatic/automatic service call Use of distress, urgency, safety and routine priorities Nature of distress Distress coordinates Time for last (distress) position update Type of subsequent communications Distress relay Distress acknowledgment Test call (for MF/HF only) Radio frequency or channel Display Receive geographical area calls Alarm Optional means for canceling a distress alert Polling Position acknowledgement Test call Test acknowledgement Data Data acknowledgement

All DSC options provided. Required on MF/HF and VHF radios used by SOLAS-regulated ships. Class A includes polling and vessel tracking, data, and numerous other functions in addition to voice. Class B:

Required on VHF and MF radios used by SOLAS-regulated ships, though most such radios in fact meet Class A. Class B required capabilities include:

Distress call All-ships call Individual station call Semi-automatic/automatic service call Use of distress, urgency, safety and routine priorities Nature of distress Distress coordinates Time for last (distress) position update Type of subsequent communications Distress relay Distress acknowledgment Test call (for MF/HF only) Radio frequency or channel Display Receive geographical area calls Alarm Optional means for canceling a distress alert

Back to Classes

Class D:

Minimum DSC capability for VHF marine radios carried by recreational boaters, commercial fishing vessels, and other non-SOLAS regulated vessels. Class D required capabilities include:

Distress call All-ships call Individual station call Use of distress, urgency, safety and routine priorities Nature of distress Distress coordinates Time for last (distress) position update Type of subsequent communications Radio VHF channel Display Receive distress relay and distress acknowledgment calls Alarm Distress acknowledgement (receive) Geographical area call (receive) Test call Test acknowledgement

Back to Classes

Class E:

Minimum DSC capability for HF marine radios carried by recreational boaters, commercial fishing vessels, and other non-SOLAS regulated vessels. Class E required capabilities include:

Distress call Individual station call Use of distress, urgency, safety and routine priorities Nature of distress Distress coordinates Time for last (distress) position update Type of subsequent communications Radio channel or frequency Display Receive distress relay and distress acknowledgment calls Test call Test acknowledgement

Back to Classes

RTCM SC101

RTCM Recommended Minimum Standard for DSC, Version 1.0, 10 Aug 1995, RTCM Paper 56-95/SC101-STD. Applies to VHF and to MF/HF. This standard is not generally recognized outside of the U.S. and should be replaced soon by the ITU Class D and E SC101 required capabilities include:

Distress call All-ships call Individual station call Use of distress and routine priorities Use of safety priority (MF/HF only) Distress coordinates Time for last (distress) position update Acknowledgment or unable to comply response Receive distress relay and distress acknowledgment calls Receive Geographical area calls Test call (MF/HF only) Alarm

Back to Classes

ITU-R Rec. M.825-3:

DSC transponder system for Vessel Traffic Services or ship- to-ship interrogation and identification. Rec. M.825 is superseded by the Universal Shipborne Automatic Identification System. Back to Classes

ITU-R Rec. M.821:

Optional expansion to DSC protocol Perhaps the most important M.821 expansion, now incorporated in most new DSC-equipped radios, improves the accuracy of distress position from 1 mile to the accuracy of your interconnected GPS receiver (about 13 meters). More information concerning DSC

USCG Notice to Mariners MF/HF DSC Guidelines (pdf) DSC Operational Procedures for Ships How Digital Selective Calling Works Maritime Mobile Service Identities Explained Why Coast Guard Supports DSC on Marine Radios





Station Type Remote Site MMSI
CAMSLANT Chesapeake VA MF/HF -- 003669995