DSC Operational Procedures for Ships

Contents

  1. Introduction
  2. Distress
  3. Urgency
  4. Safety
  5. Public correspondence
  6. Testing the equipment
  7. Special conditions and procedures for DSC communications on HF

    Introduction - Where these procedures came from

    The following procedures were adapted from the International Telecommunications Union, Radiocommunications Study Group Recommendation M.541, Operational Procedures for the use of Digital Selective-Calling (DSC) Equipment in the Maritime Mobile Service.

    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.


    Distress

    Transmission of 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 (2 187.5 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. 2 182 kHz on MF, channel 16 on VHF, while waiting for the DSC distress acknowledgment.

    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.

    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 acknowledgment 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 acknowledgment 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 acknowledgment 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.

    Distress traffic

    On receipt of a DSC distress acknowledgment 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.

    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 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 channel 16 on VHF, while waiting for the DSC distress acknowledgment.

    Acknowledgment 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".

    Acknowledgment 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 acknowledgment of a distress alert, given above.

    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 acknowledgment" 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.

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    Urgency

    Transmission of urgency messages

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

    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 (2 187.5 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.

    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.

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    Safety

    Transmission of safety messages

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

    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 out 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.

    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.

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    Public correspondence

    DSC channels for public correspondence

    VHF

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

    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.

    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 acknowledgment indicate a vacant working channel, in accordance with the DSC equipment manufacturer's instructions;

    4. transmit the DSC call.

    Repeating a call

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

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

    Acknowledgment 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 acknowledgment 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 acknowledgment format on the DSC equipment,
    3. transmit an acknowledgment 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.

    Reception of acknowledgment and further actions

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

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.

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.

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:

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.

Testing the equipment used for distress and safety on HF

The procedure for testing the ship's equipment used for DSC distress, urgency and safety calls on HF by transmitting DSC test calls on HF DSC distress channels is the same as for testing on the MF DSC distress frequency 2187.5 Hz.

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Last Revised: 3 Dec 1999

Commandant (G-SCT-2)
U.S. Coast Guard
Washington DC 20593

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