Introduction

The procedures for DSC communications on HF are in general the same as for MF and VHF. Special conditons to be taken into account when making DSC communications on HF are described in § 6.

Operating procedures may vary somewhat among different radios, depending upon how the radio is designed, how the radio's software is configured, and how the DSC processor is connected to the radio transceiver.

Contents

1. Distress
   • 1.1 Transmission of a DSC distress alert
   • 1.2 Actions on receipt of a DSC distress alert
   • 1.3 Distress traffic
   • 1.4 Transmission of a DSC distress relay alert
   • 1.5 Acknowledgement of a DSC distress relay alert received from a coast station
   • 1.6 Acknowledgement of a DSC distress relay alert received from another ship
   • 1.7 Cancellation of an inadvertent DSC distress alert
2. Urgency
   • 2.1 Transmission of urgency messages
   • 2.2 Reception of an urgency message
3. Safety
   • 3.1 Transmission of safety messages
   • 3.2 Reception of a safety message
4. Public correspondence
   • 4.1 DSC channels for public correspondence
   • 4.2 Transmission of a DSC call to a coast station or another ship
   • 4.3 Repeating a call
   • 4.4 Acknowledgement of a received call
   • 4.5 Reception of acknowledgement and further actions
5. Testing the equipment
6. Special conditions and procedures for DSC communications on HF
   • 6.1 Distress
   • 6.2 Urgency
   • 6.3 Safety

1. Distress

1.1 Transmission of a DSC distress alert

A distress alert should be transmitted if, in the opinion of the Master, the ship or a person is in distress and requires immediate assistance.

A DSC distress alert should as far as possible include the ship's last known position and the time (in UTC) when it was valid. The position and the time may be included automatically by the ship's navigational equipment or may be inserted manually.

The DSC distress alert is transmitted as follows:

1. tune the transmitter to the DSC distress channel (2187.5 kHz on MF, channel 70 on VHF)
2. if time permits, key in or select on the DSC equipment keyboard
   • the nature of distress,
   • the ship's last known position (latitude and longitude),
   • the time (in UTC) the position was valid,
   • type of subsequent distress communication (telephony),

   in accordance with the DSC equipment manufacturer's instructions;

3. transmit the DSC distress alert
4. prepare for the subsequent distress traffic by tuning the transmitter and the radiotelephony receiver to the distress traffic channel in the same band, i.e. 2182 kHz on MF, channel 16 on VHF, while waiting for the DSC distress acknowledgement.

NOTE - Some maritime MF radiotelephony transmitters shall be tuned to a frequency 1700 Hz lower than 2187.5 kHz, i.e. 2185.8 kHz, in order to transmit the DSC alert on 2187.5 kHz.

1.2 Actions on receipt of a distress alert

Ships receiving a DSC distress alert from another ship should normally not acknowledge the alert by DSC since acknowledgement of a DSC distress alert by use of DSC is normally made by coast stations only.

Only if no other station seems to have received the DSC distress alert, and the transmission of the DSC distress alert continues, the ship should acknowledge the DSC distress alert by use of DSC to terminate the call. The ship should then, in addition, inform a coast station or a coast earth station by any practicable means.

Ships receiving a DSC distress alert from another ship should also defer the acknowledgement of the distress alert by radiotelephony for a short interval, if the ship is within an area covered by one or more coast stations, in order to give the coast station time to acknowledge the DSC distress alert first.

Ships receiving a DSC distress alert from another ship shall:

1. watch for the reception of a distress acknowledgement on the distress channel (2187.5 kHz on MF and channel 70 on VHF);

2. prepare for receiving the subsequent distress communication by tuning the radiotelephony receiver to the distress traffic frequency in the same band in which the DSC distress alert was received, i.e. 2182 kHz on MF, channel 16 on VHF;

3. acknowledge the receipt of the distress alert by transmitting the following by radiotelephony on the distress traffic frequency in the same band in which the DSC distress alert was received, i.e. 2182 kHz on MF, channel 16 on VHF:
   • "MAYDAY",
   • the 9-digit identity of the ship in distress, repeated 3 times,
   • "this is",
   • the 9-digit identity or the call sign or other identification of own ship, repeated 3 times,
   • "RECEIVED MAYDAY".

NOTE - Ships out of range of a distress event or not able to assist should only acknowledge if no other station appears to acknowledge the receipt of the DSC distress alert.

1.3 Distress traffic

On receipt of a DSC distress acknowledgement the ship in distress should commence the distress traffic by radiotelephony on the distress traffic frequency (2182 kHz on MF, channel 16 on VHF) as follows:

1. "MAYDAY",
2. "this is",
3. the 9-digit identity and the call sign or other identification of the ship,
4. the ship's position in latitude and longitude or other reference to a known geographical location,
5. the nature of distress and assistance wanted,
6. any other information which might facilitate the rescue.

1.4 Transmission of a DSC distress relay alert

A ship knowing that another ship is in distress shall transmit a DSC distress relay alert if

• the ship in distress is not itself able to transmit the distress alert,
• the Master of the ship considers that further help is necessary.

The DSC distress relay alert is transmitted as follows:

1. tune the transmitter to the DSC distress channel (2187.5 kHz on MF, channel 70 on VHF),
2. select the distress relay call format on the DSC equipment,key in or select on the DSC equipment keyboard:
   • All Ships Call or the 9-digit identity of the appropriate coast station,
   • the 9-digit identity of the ship in distress, if known,
   • the nature of distress,
   • the latest position of the ship in distress, if known,
   • the time (in UTC) the position was valid, if known,
   • type of subsequent distress communication (telephony);
   • transmit the DSC distress relay call,

3. prepare for the subsequent distress traffic by tuning the transmitter and the radiotelephony receiver to the distress traffic channel in the same band, i.e. 2182 kHz on MF and channel16 on VHF, while waiting for the DSC distress acknowledgement.

1.5 Acknowledgement of a DSC distress relay alert received from a coast station

Coast stations, after having received and acknowledged a DSC distress alert, may if necessary, retransmit the information received as a DSC distress relay call, addressed to all ships, all ships in a specific geographical area, a group of ships or a specific ship.

Ships receiving a distress relay call transmitted by a coast station shall not use DSC to acknowledge the call, but should acknowledge the receipt of the call by radiotelephony on the distress traffic channel in the same band in which the relay call was received, i.e. 2182 kHz on MF, channel 16 on VHF.

Acknowledge the receipt of the distress alert by transmitting the following by radiotelephony on the distress traffic frequency in the same band in which the DSC distress relay alert was received:

1. "MAYDAY",
2. the 9-digit identity or the call sign or other identification of the calling coast station,
3. "this is",
4. the 9-digit identity or call sign or other identification of own ship,
5. "RECEIVED MAYDAY".

1.6 Acknowledgement of a DSC distress relay alert received from another ship

Ships receiving a distress relay alert from another ship shall follow the same procedure as for acknowledgement of a distress alert, given above (see 1.2).

1.7 Cancellation of an inadvertent distress alert (distress call)

A station transmitting an inadvertent distress alert shall cancel the distress alert using the following procedure:

1. Immediately transmit a DSC "distress acknowledgement" in accordance with Recommendation ITU-R M.493, 8.3.1 e.g. with own ship's MMSI inserted as identification of ship in distress. (NOTE: This feature is not yet generally available on DSC-equipped radios)
2. Cancel the distress alert aurally over the telephony distress traffic channel associated with each DSC channel on which the "distress call" was transmitted.
3. Monitor the telephony distress traffic channel associated with the DSC channel on which the distress was transmitted, and respond to any communications concerning that distress alert as appropriate.

2. Urgency

2.1 Transmission of urgency messages

Transmission of urgency messages shall be carried out in two steps:

• announcement of the urgency message,
• transmission of the urgency message.

The announcement is carried out by transmission of a DSC urgency call on the DSC distress calling channel (2187.5 kHz on MF, channel 70 on VHF).

The urgency message is transmitted on the distress traffic channel (2182 kHz on MF, channel 16 on VHF).

The DSC urgency call may be addressed to all stations or to a specific station. The frequency on which the urgency message will be transmitted shall be included in the DSC urgency call.

The transmission of an urgency message is thus carried out as follows:

Announcement:

1. tune the transmitter to the DSC distress calling channel (2187.5 kHz on MF, channel 70 on VHF);
2. key in or select on the DSC equipment keyboard:
   • All Ships Call or the 9-digit identity of the specific station,
   • the category of the call (urgency),
   • the frequency or channel on which the urgency message will be transmitted,
   • the type of communication in which the urgency message will be given (e.g. radiotelephony), in accordance with the DSC equipment manufacturer's instructions;

3. transmit the DSC urgency call.

Transmission of the urgency message:

1. tune the transmitter to the frequency or channel indicated in the DSC urgency call;
2. transmit the urgency message as follows:
   • "PAN PAN", repeated 3 times,
   • "ALL STATIONS" or called station, repeated 3 times,
   • "this is",
   • the 9-digit identity and the call sign or other identification of own ship,
   • the text of the urgency message.

2.2 Reception of an urgency message

Ships receiving a DSC urgency call announcing an urgency message addressed to all ships shall not acknowledge the receipt of the DSC call, but should tune the radiotelephony receiver to the frequency indicated in the call and listen to the urgency message.

3. Safety

3.1 Transmission of safety messages

Transmission of safety messages shall be carried out in two steps:

• announcement of the safety message,
• transmission of the safety message.

The announcement is carried out by transmission of a DSC safety call on the DSC distress calling channel (2187.5 kHz on MF, channel 70 on VHF).

The safety message is normally transmitted on the distress and safety traffic channel in the same band in which the DSC call was sent, i.e. 2182 kHz on MF, channel 16 on VHF.

The DSC safety call may be addressed to all ships, all ships in a specific geographical area or to a specific station.

The frequency on which the safety message will be transmitted shall be included in the DSC call.

The transmission of a safety message is thus carried ut as follows:

Announcement:

1. tune the transmitter to the DSC distress calling channel (2187.5 kHz on MF, channel 70 on VHF);
2. select the appropriate calling format on the DSC equipment (all ships, area call or individual call);
3. key in or select on the DSC equipment keyboard:
   • specific area or 9-digit identity of specific station, if appropriate,
   • the category of the call (safety),
   • the frequency or channel on which the safety message will be transmitted,
   • the type of communication in which the safety message will be given (e.g. radiotelephony),

   in accordance with the DSC equipment manufacturer's instructions;

4. transmit the DSC safety call.

Transmission of the safety message:

1. tune the transmitter to the frequency or channel indicated in the DSC safety call;
2. transmit the safety message as follows:
   • "SECURITE", repeated 3 times,
   • "ALL STATIONS" or called station, repeated 3 times,
   • "this is",
   • the 9-digit identity and the call sign or other identification of own ship,
   • the text of the safety message.

3.2 Reception of a safety message

Ships receiving a DSC safety call announcing a safety message addressed to all ships shall not acknowledge the receipt of the DSC safety call, but should tune the radiotelephony receiver to the frequency indicated in the call and listen to the safety message.

4. Public correspondence

4.1 DSC channels for public correspondence

4.1.1 VHF

The VHF DSC channel 70 is used for DSC for distress and safety purposes as well as for DSC for public correspondence.

4.1.2 MF

International and national DSC channels separate from the DSC distress and safety calling channel 2187.5 kHz are used for digital selective-calling on MF for public correspondence.

Ships calling a coast station by DSC on MF for public correspondence should preferably use the coast station's national DSC channel.

The international DSC channel for public correspondence may as a general rule be used between ships and coast stations of different nationality. The ships transmitting frequency is 2189.5 kHz, and the receiving frequency is 2177 kHz.

The frequency 2177 kHz is also used for digital selective-calling between ships for general communication.

4.2 Transmission of a DSC call for public correspondence to a coast station or another ship

A DSC call for public correspondence to a coast station or another ship is transmitted as follows:

1. tune the transmitter to the relevant DSC channel;
2. select the format for calling a specific station on the DSC equipment;
3. key in or select on the DSC equipment keyboard:
   • the 9-digit identity of the station to be called,
   • the category of the call (routine),
   • the type of the subsequent communication (normally radiotelephony),
   • a proposed working channel if calling another ship.

     A proposal for a working channel should NOT be included in calls to a coast station; the coast station will in its DSC acknowledgement indicate a vacant working channel, in accordance with the DSC equipment manufacturer's instructions;

4. transmit the DSC call.

4.3 Repeating a call

A DSC call for public correspondence may be repeated on the same or another DSC channel, if no acknowledgement is received within 5 min.

Further call attempts should be delayed at least 15 min, if acknowledgement is still not received.

4.4 Acknowledgement of a received call and preparation for reception of the traffic

On receipt of a DSC call from a coast station or another ship, a DSC acknowledgement is transmitted as follows:

1. tune the transmitter to the transmit frequency of the DSC channel on which the call was received,
2. select the acknowledgement format on the DSC equipment,
3. transmit an acknowledgement indicating whether the ship is able to communicate as proposed in the call (type of.communication and working frequency),
4. if able to communicate as indicated, tune the transmitter and the radiotelephony receiver to the indicated working channel and prepare to receive the traffic.

4.5 Reception of acknowledgement and further actions

When receiving an acknowledgement indicating that the called station is able to receive the traffic, prepare to transmit the traffic as follows:

tune the transmitter and receiver to the indicated working channel;
commence the communication on the working channel by:

• the 9-digit identity or call sign or other identification of the called station,
• "this is",
• the 9-digit identity or call sign or other identification of own ship.

In case the ship, in response to a call to another ship, receives an acknowledgement indicating that the other ship is not able to receive the traffic immediately, it will normally rest with the called ship to transmit a call to the calling ship when ready to receive the traffic.

5. Testing the equipment used for distress and safety

Testing on the exclusive DSC distress and safety calling frequency 2187.5 kHz should be avoided as far as possible by using other methods.

No test transmission should be made on VHF DSC calling channel 70.

Test calls should be transmitted by the ship station and acknowledged by the called coast station. Normally there would be no further communication between the two stations involved.

A test call to a coast station is transmitted as follows:

1. tune the transmitter to the DSC distress and safety calling frequency 2187.5 kHz,
2. key in or select the format for the test call on the DSC equipment in accordance with the DSC equipment manufacturer's instructions,
3. key in the 9-digit identity of the coast station to be called,
4. transmit the DSC call after checking as far as possible that no calls are in progress on the frequency,
5. wait for acknowledgement.

6. Special conditions and procedures for DSC communication on HF

General

The procedures for DSC communication on HF are - with some additions described below - equal to the corresponding procedures for DSC communications on MF/VHF.

6.1 Distress

6.1.1 Transmission of DSC distress alert

DSC distress alert should be sent to coast stations - e.g. in A3 and A4 sea areas on HF - and on MF and/or VHF to other ships in the vicinity.

The DSC distress alert should as far as possible include the ship's last known position and the time (in UTC) it was valid. If the position and time is not inserted automatically from the ship's navigational equipment, it should be inserted manually.

Ship-to-shore distress alert

Choice of HF band

Propagation characteristics of HF radio waves for the actual season and time of the day should be taken into account when choosing HF bands for transmission of DSC distress alert.

As a general rule the DSC distress channel in the 8 MHz maritime band (8414.5 kHz) may in many cases be an appropriate first choice.

Transmission of the DSC distress alert in more than one HF band will normally increase the probability of successful reception of the alert by coast stations.

DSC distress alert may be sent on a number of HF bands in two different ways:

a) either by transmitting the DSC distress alert on one HF band, and waiting a few minutes for receiving acknowledgement by a coast station;

if no acknowledgement is received within 3 min, the process is repeated by transmitting the DSC distress alert on another appropriate HF band etc.;

b) or by transmitting the DSC distress alert at a number of HF bands with no, or only very short, pauses between the calls, without waiting for acknowledgement between the calls.

It is recommended to follow procedure
a) in all cases, where time permits to do so; this will make it easier to choose the appropriate HF band for commencement of the subsequent communication with the coast station on the corresponding distress traffic channel.

Transmitting the DSC alert;

1. tune the transmitter to the chosen HF DSC distress channel (4207.5, 6312, 8414.5, 12577, 16804.5 kHz);
2. follow the instructions for keying in or selection of relevant information on the DSC equipment keyboard as described earlier;
3. transmit the DSC distress alert.

- Some maritime HF transmitters shall be tuned to afrequency 1700 Hz lower than the DSC frequencies given above in order to transmit the DSC alert on the correct frequency.

In special cases, for example in tropical zones, transmission of DSC distress alert on HF may, in addition to ship-to-shore alerting, also be useful for ship-to-ship alerting.

6.1.2 Preparation for the subsequent distress traffic

After having transmitted the DSC distress alert on appropriate DSC distress channels (HF, MF and/or VHF), prepare for the subsequent distress traffic by tuning the radiocommunication set(s) (HF, MF and/or VHF as appropriate) to the corresponding distress traffic channel(s).

If method b) described above has been used for transmission of DSC distress alert on a number of HF bands:

• take into account in which HF band(s) acknowledgement has been successfully received from a coast station;
• if acknowledgements have been received on more than one HF band, commence the transmission of distress traffic on one of these bands, but if no response is received from a coast station then the other bands should be used in turn.

The distress traffic frequencies are:

HF (kHz):

Telephony    4125      6215      8291      12290       16420
Telex        4177.5    6268    8376.5    12520       16695

MF (kHz):

Telephony     2182
Telex         2174.5

VHF: Channel 16 (156.800 MHZ).

6.1.3 Distress traffic

The procedures described earlier are used when the distress traffic on MF/HF is carried out by radiotelephony.

The following procedures shall be used in cases where the distress traffic on MF/HF is carried out by radiotelex:

1. The forward error correcting (FEC) mode shall be used unless specifically requested to do otherwise;
2. all messages shall be preceded by:
   • at least one carriage return,
   • line feed,
   • one letter shift,
   • the distress signal "MAYDAY";

3. The ship in distress should commence the distress telex traffic on the appropriate distress telex traffic channel as follows:
   • carriage return, line feed, letter shift,
   • the distress signal "MAYDAY",
   • "this is",
   • the 9-digit identity and call sign or other identification of the ship,
   • the ship's position if not included in the DSC distress alert,
   • the nature of distress,
   • any other information which might facilitate the rescue.

6.1.4 Actions on reception of a DSC distress alert on HF from another ship

Ships receiving a DSC distress alert on HF from another ship shall not acknowledge the alert, but should:

1. watch for reception of a DSC distress acknowledgement from a coast station;
2. while waiting for reception of a DSC distress acknowledgement from a coast station:

   prepare for reception of the subsequent distress communication by tuning the HF radiocommunication set (transmitter and receiver) to the relevant distress traffic channel in the same HF band in which the DSC distress alert was received, observing the following conditions:

   • if radiotelephony mode was indicated in the DSC alert, the HF radiocommunication set should be tuned to the radiotelephony distress traffic channel in the HF band concerned;
   • if telex mode was indicated in the DSC alert, the HF radiocommunication set should be tuned to the radiotelex distress traffic channel in the HF band concerned. Ships able to do so should additionally watch the corresponding radiotelephony distress channel;
   • if the DSC distress alert was received on more than one HF band, the radiocommunication set should be tuned to the relevant distress traffic channel in the HF band considered to be the best one in the actual case. If the DSC distress alert was received successfully on the 8 MHz band, this band may in many cases be an appropriate first choice;

3. if no distress traffic is received on the HF channel within 1 to 2 min, tune the HF radiocommunication set to the relevant distress traffic channel in another HF band deemed appropriate inthe actual case;
4. if no DSC distress acknowledgement is received from a coast station within 3 min, and no distress communication is observed going on between a coast station and the ship in distress:
   • transmit a DSC distress relay alert,
   • inform a Rescue Coordination Center via appropriate radiocommunications means.

6.1.5 Transmission of DSC distress relay alert

In case it is considered appropriate to transmit a DSC distress relay alert:

1. considering the actual situation, decide in which frequency bands (MF, VHF, HF) DSC distress relay alert(s) should be transmitted, taking into account ship-to-ship alerting (MF,VHF) and ship-to-shore alerting;
2. tune the transmitter(s) to the relevant DSC distress channel, following the procedures described above;
3. follow the instructions for keying in or selection of call format and relevant information on the DSC equipment keyboard as described earlier;
4. transmit the DSC distress relay alert.

6.1.6 Acknowledgement of a HF DSC distress relay alert received from a coast station

Ships receiving a DSC distress relay alert from a coast station on HF, addressed to all ships within a specified area, should NOT acknowledge the receipt of the relay alert by DSC, but by radiotelephony on the telephony distress traffic channel in the same band(s) in which the DSC distress relay alert was received (see 1.5).

6.2 Urgency

Transmission of urgency messages on HF should normally be addressed:

• either to all ships within a specified geographical area,
• or to a specific coast station.

Announcement of the urgency message is carried out by transmission of a DSC call with category urgency on the appropriate DSC distress channel.

The transmission of the urgency message itself on HF is carried out by radiotelephony or radiotelex on the appropriate distress traffic channel in the same band in which the DSC announcement was transmitted.

6.2.1 Transmission of DSC announcement of an urgency message on HF

1. choose the HF band considered to be the most appropriate, taking into account propagation characteristics for HF radiowaves at the actual season and time of the day; the 8 MHZ band may in many cases be an appropriate first choice;
2. tune the HF transmitter to the DSC distress channel in the chosen HF band;
3. key in or select call format for either geographical area call or individual call on the DSC equipment, as appropriate;
4. in case of area call, key in specification of the relevant geographical area;
5. follow the instructions for keying in or selection of relevant information on the DSC equipment keyboard as described earlier, including type of communication in which the urgency message will be transmitted (radiotelephony or radiotelex);
6. transmit the DSC call; and
7. if the DSC call is addressed to a specific coast station, wait for DSC acknowledgement from the coast station. If acknowledgement is not received within a few minutes, repeat the DSC call on another HF frequency deemed appropriate.

1. tune the HF transmitter to the distress traffic channel (telephony or telex) indicated in the DSC announcement;
2. if the urgency message is to be transmitted using radiotelephony, follow the procedure described in § 2. 1;
3. if the urgency message is to be transmitted by radiotelex, the following procedure shall be used:
4. use the forward error correcting (FEC) mode unless the message is addressed to a single station whose radiotelex identity number is known;
5. commence the telex message by:
   • at least one carriage return, line feed, one letter shift,
   • the urgency signal "PAN PAN",
   • "this is",
   • the 9-digit identity of the ship and the call sign or other identification of the ship,
   • the text of the urgency message.

Announcement and transmission of urgency messages addressed to all HF equipped ships within a specified area may be repeated on a number of HF bands as deemed appropriate in the actual situation.

6.2.3 Reception of an urgency message

Ships receiving a DSC urgency call announcing an urgency message shall NOT acknowledge the receipt of the DSC call, but should tune the radiocommunication receiver to the frequency and communication mode indicated in the DSC call for receiving the message.

6.3 Safety

The procedures for transmission of DSC safety announcement and for transmission of the safety message are the same as for urgency messages, described for Urgency, except that:

• in the DSC announcement, the category SAFETY shall be used,
• in the safety message, the safety signal "SECURITE" shall be used instead of the urgency signal "PAN PAN".

6.4 Public correspondence on HF

The procedures for DSC communication for public correspondence on HF are the same as for MF.

Propagation characteristics should be taken into account when making DSC communication on HF.

International and national HF DSC channels different from those used for DSC for distress and safety purposes are used for DSC for public correspondence.

Ships calling a HF coast station by DSC for public correspondence should preferably use the coast station's national DSC calling channel.

6.5 Testing the equipment used for distress and safety on HF