DSC PUBLIC CORRESPONDENCE
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.
DSC channels for public correspondence
The VHF DSC channel 70 is used for DSC for distress and safety purposes as well as for DSC for public correspondence.
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:
tune the transmitter to the relevant DSC channel;
select the format for calling a specific station on the DSC equipment;
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;
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:
tune the transmitter to the transmit frequency of the DSC channel on which the call was received,
select the acknowledgment format on the DSC equipment,
transmit an acknowledgment indicating whether the ship is able to communicate as proposed in the call (type of communication and working frequency),
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:
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,
the 9-digit identity or call sign or other identification of own ship.
It will normally rest with the ship to call again a little later in case the acknowledgment from the coast station indicates that the coast station is not able to receive the traffic immediately.
In case the ship, in response to a call to another ship, receives an acknowledgment 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.