Summary
The Recommendation contains the operational procedures for digital selective-calling (DSC) equipment whose technical characteristics are given in Recommendation ITU-R M.493. The Recommendation contains four annexes. In Annexes 1 and 2 the provisions and procedures are described for distress and safety calls and for non-distress and safety calls, respectively. In Annexes 3 and 4 the operational procedures for ships and for coast stations are described and Annex 5 lists the frequencies to be used for DSC.
The ITU Radiocommunication Assembly,
considering
a) Resolution No.311 and Recommendation No.312 of the World Administrative Radio Conference(Geneva, 1979) (WARC-79),
b) that digital selective-calling (DSC) will be used as described in Recommendation ITU-R M.493:
c) that the requirements of Chapter IV of the 1988 Amendments to the International Convention for the safety of Life at Sea (SOLAS), 1974, for the Global Maritime Distress and Safety System (GMDSS) are based on the use of DSC for distress alerting on terrestrial frequencies and that operational procedures are necessary for transition to, and implementation of, that system;
d) that, as far as is practicable, operational procedures in all frequency bands and for all types of communications should be similar;
e) that DSC may provide a useful supplementary means of transmitting a distress call in addition to the provisions of transmitting the distress call by existing methods and procedures in the Radio Regulations (RR);
f) that conditions when alarms have to be actuated should be specified,
recommends
1 that the technical characteristics of equipment used for DSC in the maritime mobile service should be in conformity with the relevant ITU-R Recommendations;
2 that the operational procedures to be observed in the MF, HF and VHF hands for DSC should be in accordance with Annex 1 for distress and safety calls and Annex 2 for other calls:
3 that provisions should be made at stations equipped for DSC for:
3.1 the manual entry of address, type of call, category and various messages into a DSC sequence;
3.2 the verification and if necessary the correction of such manually formed sequences:
3.3 a specific aural alarm and visual indication to indicate receipt of a distress or urgency call or a call having distress category. It should not be possible to disable this alarm and indication. Provisions should be made to ensure that they can be reset only manually;
3.4 aural alarm(s) and visual indication for calls other than distress and urgency. The aural alarm(s) may be capable of being disabled;
3.5 such visual indication to indicate:
3.5.1 type of received call address (to all stations, to a group of stations, geographical, individual);
3.5.2 category;
3.5.3 identity of calling station:
3.5.4 numerical or alpha-numerical type of information, e.g. frequency information and telecommand;
3.5.5 type of "end of sequence" character;
3.5.6 detection of errors, if any;
3.6 monitoring the VHF channel used for digital selective-calling purposes to determine the presence of a signal and, except for distress and safety calls, provide facilities for automatically preventing the transmission of a DSC call until the channel is free;
3.7 ship originated routine all-ships calls on VHF should be transmitted at a power level of 1W or less. Integrated VHF DSC equipment should automatically reduce power for transmission of these calls;
4 that the equipment should be simple to operate;
5 that the operational procedures given in Annex 3, which are based on the relevant procedures tent Annexes 1 and 2 and from the RR, be used as guidance for ships and coast stations;
6 that the frequencies used for distress and safety purposes using DSC are those contained in Annex 4 to this Recommendation (see also RR Article 38 (Appendix S13, Part A2)).
NOTE 1 - The following definitions are used throughout this Recommendation:
Single frequency: the same frequency is used for transmission and reception;
Paired frequencies: frequencies which are associated in pairs; each pair consisting of one transmitting and one receiving frequency; International DSC frequencies: those frequencies designated in the RR for exclusive use for DSC on an international basis;
National DSC frequencies: those frequencies assigned to individual coast stations or a group of station on which DSC is permitted (this may include working frequencies as well as calling frequencies). The use of these frequencies must be in accordance with the RR;
Automatic DSC operation at a ship station: a mode of operation employing automatic tunable transmitters and receivers suitable for unattended operation, which provide for automatic call acknowledgements upon reception of a DSC and automatic transfer to the appropriate working frequencies;
Call attempt: one or a limited number of call sequences directed to the same stations on one, or more frequencies and within a relatively short time period (e.g. a few minutes). A call attempt is considered unsuccessful if a calling sequence contains the symbol RQ at the end of the sequence and no acknowledgement is received in this time interval.