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Recommendation 541-8
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(1978-1982-1986-1990-1992-1994-1995-1996-1997)
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OPERATIONAL PROCEDURES FOR THE USE OF DIGITAL SELECTIVE-CALLING EQUIPMENT IN THE MARITIME MOBILE SERVICE
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(Question ITU-R 9/8)
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ANNEX 4
Operational procedures for coast stations for DSC communications on MF, HF and VHF
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Introduction
Procedures for DSC communications on MF and VHF an described in з1 to 5 below. The procedures for DSC communications on HF are in general the same as for MF and VHF. Special conditions to be taken into account when making DSC communications on HF are described in з6 below.
1 Distress (see Note 1)
1.1 Reception of a DSC distress alert (distress call)
The transmission of a distress alert indicates that a mobile unit (a ship, aircraft or other vehicle) or a person is in distress and requires immediate assistance. The distress alert is a digital selective call using a distress call format (distress call). Coast stations in receipt of a distress call shall ensure that it is routed as soon as possible to an RCC. The receipt of a distress call is to be acknowledged as soon as possible by the appropriate coast station.
NOTE 1 These procedures assume that the RCC is sited remotely from the DSC coast station; where this is not the case, appropriate amendments should be made locally.
1.2 Acknowledgement of a DSC distress alert (distress call)
The coast station shall transmit the acknowledgement on the distress calling frequency on which the call was received and should address it to all ships. The acknowledgement shall include the identification of the ship whose distress call is being acknowledged. The acknowledgement of a DSC distress call is transmitted as follows:
- use a transmitter which is tuned to the frequency on which the distress call was received;
- in accordance with the DSC equipment manufacturer's instructions, key in or select on the DSC equipment keyboard (See Note 1): |
- distress call acknowledgement,
- 9-digit identity of the ship in distress,
- nature of distress,
- distress coordinates,
- the time (in UTC) when the position was valid.
NOTE 1 - Some or all of this information might be included automatically by the equipment;
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- transmit the acknowledgement;
- prepare to handle the subsequent distress traffic by setting watch on radiotelephony and, if the "mode of subsequent communication" signal in the received distress call indicates teleprinter, also on NBDP, if the coast station is fitted with NBDP. In both cases, the radiotelephone and NBDP frequencies should be those associated with the frequency on which the distress call was received (on MF 2182 kHz for radiotelephony and 2174.5 kHz for NBDP, on VHF 156.8 MHz/channel 16 for radiotelephony; there is no frequency for NBDP on VHF).
1.3 Transmission of a DSC distress relay alert(distress relay call)
Coast stations shall initiate and transmit a distress relay call in any of the following cases:
- when the distress of the mobile unit has been notified to the coast station by other means and a broadcast alert to shipping is required by the RCC; and
- when the person responsible for the coast station considers that further help is necessary (close cooperation with the appropriate RCC is recommended under such conditions).
In the cases mentioned above, the coast station shall transmit a shore-to-ship distress relay call addressed, as appropriate, to all ships, to a selected group of ships, to a geographical area or to a specific ship.
The distress relay call shall contain the identification of the mobile unit in distress, its position and other information which might facilitate rescue.
The distress relay call is transmitted as follows:
- use a transmitter which is tuned to the frequency for DSC distress calls (2187.5 kHz on MF, 156.525 MHz/channel 70 on VHF);
- in accordance with the DSC equipment manufacturer's instructions, key in or select on the DSC equipment keyboard (see Note 1 of з1.2 of this Annex): |
- distress relay call,
- the format specifier (all ships, group of ships, geographical area or individual station),
- if appropriate, the address of the ship, group of ships or geographical area (not required if the format specifier is "all ships"),
- 9-digit identity of the ship in distress, if known,
- nature of distress,
- distress coordinates,
- the time (in UTC) when the position was valid:
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- transmit the distress relay call;
- prepare for the reception of the acknowledgements by ship stations and for handling the subsequent distress traffic by switching over to the distress traffic channel in the same band, i.e. 2182 kHz on MF, 156.8 MHz, channel 16 on VHF.
1.4 Reception or a distress relay alert (distress relay call)
If the distress relay call is received from a ship station, coast stations on receipt of the distress relay call shall ensure that the call is routed as soon as possible to an RCC. The receipt of the distress relay call is to be acknowledged as soon as possible by the appropriate coast station using a DSC distress relay acknowledgement addressed to the ship station. If the distress relay call is received from a coast station, other coast stations will normally not have to take further action.
2 Urgency
2.1 Transmission of a DSC announcement
The announcement of the urgency message shall be made on one or more of the distress and safety calling frequencies using DSC and the urgency call format.
The DSC urgency call may be addressed to all ships, to a selected group of ships, to a geographical area or to a specific ship.
The frequency on which the urgency message will be transmitted after the announcement shall be included in the DSC urgency call. The DSC urgency call is transmitted as follows:
- use a transmitter which is tuned to the frequency for DSC distress calls (2187.5 kHz on MF, 156.525 MHz/channel 70 on VHF):
- in accordance with the DSC equipment manufacturer's instructions, key in or select on the DSC equipment keyboard (see Note 1 of з1.2 of this Annex): |
- the format specifier (all ships call, group of ships, geographical area or individual station),
- if appropriate, the address or the ship, group of ships or geographical area (not required if the format specifier is "all ships"),
- the category of the call (urgency).
- the frequency or channel on which the urgency message will he transmitted,
- the type of communication in which the urgency message will be transmitted (radiotelephony);
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- transmit the DSC urgency call.
After the DSC announcement, the urgency message wilt be transmitted on the frequency indicated in the DSC call.
3 Safety
3.1 Transmission of a DSC announcement
The announcement of the safety message shall be made on one or more of the distress and safety calling frequencies using DSC and the safety call format.
The DSC safety call may be addressed to all ships, to a group of ships, to a geographical area or to a specific ship. The frequency on which the safety message wilt be transmitted after the announcement shall be included in the DSC safety call.
The DSC safety call is transmitted as follows:
- use a transmitter which is tuned to the frequency for DSC distress calls (2187.5 kHz on MF, 156.525 MHz/channel 70 on VHF);
- in accordance with the DSC equipment manufacturer's instructions, key in or select on the DSC equipment keyboard (see Note 1 of з1.2 of this Annex): |
- the format specifier (all ships call, group of ships, geographical area or individual station),
- if appropriate. the address of the ship, group of ships or geographical area (not required if the format specifier is "all ships"),
- 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 transmitted (radiotelephony);
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- transmit the DSC safety call.
After the DSC announcement, the safety message will be transmitted on the frequency indicated in the DSC call.
4 Public correspondence
4.1 DSC frequencies/channels for public correspondence
4.1.1 VHF
The frequency 156.525 MHz/channel 70 is used for DSC for distress and safety purposes. It may also be used for calling purposes other than distress and safety, e.g. public correspondence.
4.1.2 MF
For public correspondence national and international frequencies are used which are different from the frequencies used for distress and safety purposes.
When calling ship stations by DSC, coast stations should use for the call, in the order of preference:
- a national DSC channel on which the coast station is maintaining watch;
- the international DSC calling channel, with the coast station transmitting on 2177 kHz and receiving on 2189.5 kHz. In order to reduce interference on this channel, it may be used as a general rule by coast stations to call ships of another nationality, or in cases where it is not known on which DSC frequencies the ship station is maintaining watch.
4.2 Transmission of a DSC call to a ship
The DSC call is transmitted as follows:
- use a transmitter which is tuned to the appropriate calling frequency;
- in accordance with the DSC equipment manufacturer's instructions, key in or select on the DSC equipment keyboard (see Note 1 of з1.2 of this Annex): |
- the 9-digit identity of the ship to be called,
- the category of the call (routine or ship's business),
- the type of subsequent communication (radiotelephony),
- working frequency information;
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- after checking as far as possible that there are no calls in progress, transmit the DSC call.
4.3 Repeating a call
Coast stations may transmit the call twice on the same calling frequency with an interval of at least 45 s between the two calls, provided that they receive no acknowledgement within that interval.
If the station called does not acknowledge the call after the second transmission, the call may be transmitted again on the same frequency after a period of at least 30 min or on another calling frequency after a period of at least 5 min.
4.4 Preparation for exchange of traffic
On receipt of a DSC acknowledgement with the indication that the called ship station can use the proposed working frequency, the coast station transfers to the working frequency or channel and prepares to receive the traffic.
4.5 Acknowledgement of a received DSC call
Acknowledgements shall normally be transmitted on the frequency paired with the frequency of the received call. If the same call is received on several calling channels, the most appropriate channel shall be chosen for transmission of the acknowledgement.
The acknowledgement of a DSC call is transmitted as follows:
- use a transmitter which is tuned to the appropriate frequency;
- in accordance with the DSC equipment manufacturer's instructions, key in or select on the DSC equipment keyboard (see Note 1 of з1.2 of this Annex): |
- the format specifier (individual station),
- 9-digit identity of the calling ship, - the category of the call (routine or ship's business),
- if able to comply immediately on the working frequency suggested by the ship station, the same frequency information as in the received call,
- if no working frequency was suggested by the calling ship station, then the acknowledgement should include a channel/frequency proposal,
- if not able to comply on the working frequency suggested, but able to comply immediately on an alternative frequency, the alternative working frequency,
- if unable to comply immediately the appropriate information in that regard;
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- transmit the acknowledgement (after checking as far as possible that there are no calls in progress on the frequency selected) after a delay of at least 5 s, but not later than 41/2 min.
4.6 Preparation for exchange or traffic
After having transmitted the acknowledgement, the coast station transfers to the working frequency or channel and prepares to receive the traffic.
5 Testing the equipment used for distress and safety calls
Testing on the exclusive DSC distress and safety calling frequencies should be avoided as far as possible by using other methods. There should be no test transmissions on the DSC calling frequency 156.525 MHz/channel 70. However, when testing on the exclusive DSC distress and safety calling frequency 2187.5 kHz is unavoidable, it should be indicated that these are test transmissions (e.g. special test calls).
Test calls should be transmitted by the ship station and acknowledged by the called coast station. Normally there would be no further communications between the two stations involved.
Acknowledgement of a DSC test call
The acknowledgement of a DSC test call is transmitted as follows:
- use a transmitter which is tuned to 2187.5 kHz;
- in accordance with the DSC equipment manufacturer's instructions, key in or select on the DSC equipment keyboard: |
- test call acknowledgement,
- 9-digit identity of the calling ship station;
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- transmit the acknowledgement.
6 Special conditions and procedures for DSC communication on HF
General
The procedures for DSC communication on HF are with some additions described in з6.1 to 6.4 below - equal to the corresponding procedures for DSC communications on MF/VHF.
Due regard to the special conditions described in з6.1 to 6.4 should be given when making DSC communications on HF.
6.1 Distress
6.1.1 Reception and acknowledgement of a DSC distress alert on HF
Ships in distress may in some cases transmit the DSC distress alert on a number of HF bands with only snort intervals between the individual calls.
The coast station shall transmit DSC acknowledgement on all HF DSC distress channels on which the DSC alert was received in order to ensure as far as possible that the acknowledgement is received by the ship in distress and by all ships which received the DSC alert.
6.1.2 Distress traffic
The distress traffic should, as a general rule, be initiated on the appropriate distress traffic channel (radiotelephony or NBDP) in the same band in which the DSC alert was received.
For distress traffic by NBDP the following rules apply:
- all messages shall be preceded by at least one carriage return, line feed, one letter shift end the distress signal MAYDAY;
- FEC broadcast mode should normally be used.
ARQ mode should be used only when considered advantageous to do so in the actual situation and provided that the radlotelex number of the ship is known.
6.1.3 Transmission of DSC distress relay alert on HF
HF propagation characteristics should be taken into account when choosing HF band(s) for transmission of DSC distress relay alert.
IMO Convention ships equipped with HF DSC for distress and safety purposes are required to keep continuous automatic DSC watch on the DSC distress channel in the 8 MHz band and on at least one of the other HF DSC distress channels.
In order to avoid creating on board ships uncertainty regarding on which band the subsequent establishment of contact and distress traffic should be initiated, the HF DSC distress relay alert should be transmitted on one HF band at a time and the subsequent communication with responding ships be established before eventually repeating the DSC distress relay alert on another HF band.
6.2 Urgency
6.2.1 Transmission of urgency announcement and message on HF
For urgency messages by NBDP the following apply:
- the urgency message shall be preceded by at least one carriage return, line feed, one letter shift, the urgency signal PAN PAN and the identification of the coast station;
- FEC broadcast mode should normally be used.
ARQ mode should be used only when considered advantageous to do so in the on and provided that the radiotelex number of the ship is known.
6.3 Safety
6.3.1 Transmission or safety announcements and messages on HF
For safety messages by NBDP the following apply:
- the safety message shall be preceded by at least one carriage return, line feed, one letter shift, the safety signal SECURITE and the identification of the coast station;
- FEC broadcast mode should normally be used.
ARQ mode should be used only when considered advantageous to do so in the actual situation and provided that the radiotelex number of the ship is known.
6.4 Testing the equipment used for distress and safety
The procedures for ships testing their equipment used for DSC distress, urgency and safety calls on HF DSC distress channels and the acknowledgement of the test call by the coast station are the same as for testing on the MF DSC distress frequency 2187.5 kHz. |
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ANNEX 5
Frequencies used for DSC
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1 The frequencies used for distress and safety purposes using DSC are as follows (see also RR Article 38(Appendix S13, Part A2)):
2187.5 kHz
4207.5 kHz
6312 kHz
8414.5 kHz
12577 kHz
16804.5 kHz
156.525 MHz (Note 1)
NOTE 1 The frequency 156.525 MHz may also be used for DSC purposes other than distress and safety.
2 The frequencies assignable on an international basis to ship and coast stations for DSC, for purposes other than distress and safety, are as follows:
2.1 Ship stations (see Note 1) |
| 458.5 |
а |
а |
kHz |
| 2177 (Note 2) |
2189.5 |
а |
kHz |
| 4208 |
4208.5 |
4209 |
kHz |
| 6312.5 |
6313 |
6313.5 |
kHz |
| 8415 |
8415.5 |
8416 |
kHz |
| 12577.5 |
12578 |
12578.5 |
kHz |
| 16805 |
16805.5 |
16806 |
kHz |
| 18898.5 |
18899 |
18899.5 |
kHz |
| 22374.5 |
22375 |
22375.5 |
kHz |
| 25208.5 |
25209 |
25209.5 |
kHz |
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а |
156.525(Note 3) |
MHz |
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| 2.2 Coast stations (see Note 1) |
| 455.5 |
а |
а |
kHz |
| 2177 |
а |
а |
kHz |
| 4219.5 |
4220 |
4220.5 |
kHz |
| 6331 |
6331.5 |
6332 |
kHz |
| 8436.5 |
8437 |
8437.5 |
kHz |
| 12657 |
12657,5 |
12658 |
kHz |
| 16903 |
16903.5 |
16904 |
kHz |
| 19703.5 |
19704 |
19704.5 |
kHz |
| 22444 |
22444.5 |
22445 |
kHz |
| 26121 |
26121.5 |
26122 |
kHz |
| а |
а |
156.525(Note 3) |
MHz |
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NOTE 1 - The following (kHz) paired frequencies (for ship/coast stations) 4208/4219.5, 6312.5/6331, 8415/8436.5, 12577.5/12657, 16805/16903, 18898.5/19703.5, 22374.5/22444 and 25208.5/26121 are the first choice international frequencies for DSC.
NOTE 2 - The frequency 2177 kHz is available to ship stations for intership calling only.
NOTE 3 - The frequency 156.525 MHz is also used for distress and safety purposes (see Note 1 of з1 of this Annex).
3 In addition to the frequencies listed in з2 above, appropriate working frequencies in the following bands may be used for DSC: |
| 415-526.5 |
kHz |
(Regions 1 and 3) |
| 415-525 |
kHz |
(Region 2) |
| 1606.5-4000 |
kHz |
(Regions 1 and 3) |
| 1605-4000 |
kHz |
(Region 2)(For the band 1605-1625 kHz, see RR No.480 (S5.89)) |
| 4000-27500 |
kHz |
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| 156-174 |
kHz |
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