1. Chapter 4 Terrestrial Communication Terminal In the GMDSS, terrestrial radiocommunication system refers to MF/HF/VHF communication systems which are used for distress alerting; SAR coordinating communications; on-scene communications and general radio communications, to carry out radiotelephone, radiotelex and digital selective calling services. The system consists of the following three subsystems: (a) MF communication subsystem, which is used for medium-range service; (b) HF communication subsystem, which is used for long-range service; and (c) VHF communication subsystem, which is used for short-range service.
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2. Long-Range Service DSC, NBDP( telex ), SSB Use of HF provides a long-range service in both the ship-to-shore and shore-to-ship directions. In areas covered by Inmarsat it can be used as an alternative to satellite communications and outside these areas it provides the only long-range communication capability. Frequencies have been designated in the 4, 6, 8, 12 and 16 MHz bands for this service.
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3. Medium-Range Service DSC, NBDP( telex ), SSB, NAVTEX A medium-range service is provided on frequencies in the 2 MHz band. In the ship-to-shore, ship-to-ship and shore-to-ship directions, kHz will be used for distress alerts and safety calls by DSC, and 2182 kHz will be used for distress and safety traffic by radiotelephony, including SAR coordinating functions and on-scene communications kHz will be used for distress and safety traffic by radiotelex (NBDP). Frequencies near 500 kHz will be used in the shore-to-ship direction. The frequency 518 kHz is being used to transmit navigational and meteorological warnings in the NAVTEX system.
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4. Short-Range Service DSC, VHF Telephony, VHF EPIRB, SART VHF provides a short-range service on the following frequencies : (a)    MHz (channel 70) for distress alerts and safety calls by DSC (b) MHz (channel 16) for distress and safety traffic by radiotelephony, including SAR coordinating functions and on-scene communications.
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5. 4.2 DIGITAL SELECTIVE CALLING (DSC)
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7. Basic Description of DSC DSC is an automatic calling system which allows a specific station to be contacted and made aware that a station wishes to communicate with it. It is a digital calling system employing an error detecting code used by ships and coast stations in the MF, HF and VHF maritime communication bands. In addition to calls to specific stations the system can also be used to make "all ships" calls, this is of particular significance for it is used for DSC distress alerting in GMDSS.
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8. DSC is only an alerting signal and the communication which follows the call will be made on an appropriate frequency band using either RT or telex. Thus in the original DSC call the transmission mode of the subsequent communication may be included , this allows the receiving station to identify whether radiotelephony or radiotelex is to be used. The frequency of the subsequent communication may also be included indicating to receiving stations the appropriate frequency to which to tune for subsequent distress traffic.
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9. DSC frequencies calling frequencies The frequencies used for distress and safety purposes using digital selective calling are as follows: kHz ( MF) kHz ( HF) kHz ( HF) kHz ( HF) kHz ( HF) kHz (HF) and Channel 70 VHF
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10. Method of Calling (other than distress, urgency or safety call) The call shall contain information indicating the station or stations to which the call is directed, and the identification of the calling station. The call should also contain information indicating the type of communication to be set up and may include supplementary information such as a proposed working frequency or channel; this information shall always be included in calls from coast stations, which shall have priority for that purpose.
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11. Subsequent communication
Calling station
Called station
Calling
Identification of called station
Identification of calling station
Subsequent type of communication
Proposed working frequency
Acknowledge
Subsequent communication
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12. The method used to transmit a DSC call for public correspondence to coast station or another ship is as follows : (a) tune transmitter to the relevant DSC channel; (b) select the format for calling a specific station on the DSC controller (individual call, group call, area call or distress call); (c) on the keyboard select (or key in): • the nine digit MMSI of the station to be called; • the category of the call (routine) ; • the type of subsequent communication (usually RT) • a proposed working channel if calling another ship. ( Note that all proposed working channel should not be included in a call to a coast station. The coast station will indicate a free working channel in its DSC acknowledgement. ) (d) transmit the DSC call.
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13. Acknowledgement of Calls The reply to a digital selective call requesting an acknowledgement shall be made by transmitting an appropriate acknowledgment using DSC techniques, acknowledgements may be manual or automatic. Transmission of the calling signal must cease as soon as an acknowledgement has been received. 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 shall be chosen to transmit the acknowledgement.
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14. 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: * Tune the transmitter to the transmit frequency of the DSC channel on which the call was received; * Select the acknowledgement format on the DSC equipment; * Transmit an acknowledgement 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, now tune the transmitter and the radiotelephony receiver to the indicated working channel and prepare for receiving the traffic.
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15. when an acknowledgement has been received which indicates that the called station is ready to receive traffic, the ship's transmitter should be prepared for traffic as follows: (a) tune transmitter and receiver to the agreed working channel indicated; (b) initiate communication on this working channel as follows: • the nine digit MMSI or call sign or other identification of the called station; • this is; • the nine digit MMSI or call sign or other identification of the calling station (own ship).
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16. If the station called does not acknowledge the call, the call may be transmitted again on the same calling frequency (or another frequency) after a period of at least five minutes (five seconds in automated VHF or UHF systems). Normally it should not then be repeated until after a further interval of 15 minutes.
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17. Public correspondence by ship stations 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 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.
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18. Public correspondence by coast stations DSC Frequencies/Channels for Public Correspondence VHF The frequency 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 MF For public correspondence national and international frequencies are used which are different from the frequencies used for distress and safety purposes (2187.5KHz). When calling ship stations by DSC, coast stations should use for the call, in the order of preference: a) a national DSC channel on which the coast station is maintaining watch; b) the international DSC calling channel, with the coast station transmitting on 2177 kHz and receiving on 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.
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19. NARROW BAND DIRECT PRINTING (NBDP) Introduction NBDP relates to the terrestrial radio telex services in the MF and HF marine radio bands. Telex is also available using satellite communications which is covered by INMARSAT system. Marine terrestrial radio telex is also referred to as "Narrow Band Direct Printing" (NBDP) or sometimes Radio Teletype (RTT).
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20. The procedures specified in this section should be employed for routine communication except in cases of distress, urgency or safety. For communication between two stations, the ARQ (Automatic Repetition Request) mode should be used when available. (point to point) For transmissions from one coast or ship station to two or more other stations, the FEC (Forward Error Correcting) mode should be used when available. (point to surface)
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21. FEC (Forward Error Correcting) mode
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22. ARQ (Automatic Repetition Request) modeB
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23. Before transmitting a station should take precautions to ensure that its emissions will not interfere with transmissions already in progress. If interference is likely, the station shall wait for an appropriate break in the communications in progress.
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24. Selcall numbers Each ship station and coast radio station having radio telex facilities is assigned a unique selcall number in addition to its international call sign. The first number (s) of the selcall indicates the country to which a particular station belongs. Ship selcall numbers have five digits, e. g Coast station selcall numbers have four digits, e.g China allocation of selcall numbers is as follows: Ship stations: to Coast stations: 2010 to 2039 Ships' selcall numbers will be found in ITU List of Ship Stations and coast station selcall numbers will be found in Volume 1 and ITU List of Coast Stations.
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25. A B
Send Ship B’s selcall number
Answer own’s answerback
Telex answerbacks To ensure that an operator has been connected to the correct coast radio station, ship station, or telex subscriber ashore, it is normal to exchange answerbacks at the commencement of a telex link. Each telex installation has a unique answerback to identify itself and this is programmed into the equipment.
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26. When, for example, the automatic radio telex facility controlled by Coastal radio station is accessed, the following answerback will be received: “2010 XSG CN". Where: is Shanghai radio's selcall number; XSG indicates the identification of Shanghai radio; and CN indicates the country— in this case China.   A ship's answerback might be “ BRYC X" . Where: indicates the ship's selcall number (MV. LIUHE); BRYC is the ship's international call sign; and X indicates that it is a maritime mobile station. Telex subscribers ashore have answerbacks which include their telex number followed by a short word or group of letters indicating the name of the company or Organisation and finally the country identifier, e.g SMTCO CN. (Shanghai Maritime Transport CO.)
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27. Modes of telex operation Radio circuits are liable to interference, fading or bursts of static which can mutilate sections of a telex message. An effective means of error detection and correction is therefore needed. There are two main modes of operation namely ARQ and FEC.   ARQ (Automated Repetition request) ARQ means Automatic Repetition request and provides error detection and error correction. However, it requires both communicating stations to have their respective transmitters and receivers active simultaneously. This mode is normally restricted in use between two stations e. g. a ship and a coast station or perhaps two ships.
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28. ARQ (Automated Repetition request)B
message
Ship A’ transmitter
Ship B’ transmitter
Ship A’ receiver
Ship B’ receiver
Error detection code
If no error, ship A will send next message,
otherwise the existing message will re-sent.
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29. FEC (Forward Error Correction) FEC means Forward Error Correction and provides error detection only. If any doubtful letters occur in the text, a gap (or sometimes an asterisk) will appear. With FEC the receiving station (s) do not need an active transmitter. This mode of operation is therefore ideal for broadcasting information to numerous stations simultaneously and it is used for sending traffic lists, weather and navigational warnings etc. It is therefore sometimes referred to as the "broadcast mode" and is the preferred telex mode for distress, urgency and safety messages.
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30. same message sent at second time FEC (Forward Error Correction) B
message
Ship A’ transmitter
Ship B’ receiver
Ship A sends each message twice only.
If two message received by Ship B is identical, ship B will print it.
same message sent at second time
FEC (Forward Error Correction)
CFEC: collective FEC
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31. SELFEC (selective FEC, SFEC) A derivation of FEC is called SELFEC
SELFEC (selective FEC, SFEC) A derivation of FEC is called SELFEC. Again the recipient's transmitter does not have to be active and it is similar to FEC in all respects except that the transmission is addressed to a particular receiving station (i.e. by addressing the call to the appropriate selcall number). It is an ideal mode of transmission for ships to receive telex messages whilst in a port where the use of transmitters may be restricted or forbidden.
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32. Telex Frequencies 518kHz In the MF maritime mobile service 518 kHz is used exclusively for the transmission by coast stations of meteorological and navigational warnings and urgent information to ships by telex (international NAVTEX system).   kHz Exclusively reserved for distress and safety traffic using telex in MF band. It should be used for ship-to-ship on-scene communications in FEC mode kHz; 6268 kHz; kHz; kHz; kHz In the HF maritime mobile bands these frequencies are reserved exclusively for distress and safety using telex.   4210 kHz; 6314 kHz; kHz; kHz; kHz; 22376kHz; kHz In the HF maritime mobile bands these frequencies are reserved exclusively for the transmission by coast stations of maritime safety information by telex in FEC mode.
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33. Telex transmission format ( ARQ mode) Where the appropriate facilities are provided by the coast station, traffic may be exchanged with the telex network either: (a) in conversational mode where the stations a connected directly, either automatically or manually; or (b) in a store and forward mode where traffic is stored at the coast station until the circuit to the called subscriber can be set up, either automatically or under manual control.
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34. International telex network
Coastal radio station
International telex network
Subscriber
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35. Operation in FEC mode Messages in Forward Error Correction (FEC) mode may be sent, by prior arrangement, from a coast station or ship station to one or more ship stations in the following cases: (a) where a receiving ship station is not able to use its transmitter or is not permitted to do so; (b) where the message is intended for more than one ship; (c) where unattended reception of the message in the FEC mode is necessary and automatic acknowledgement is not required.
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36. MARITIME MOBILE RADIO TELEPHONY (RT) Maritime radiotelephony refers to radio telephone communication, when using MF, HF, VHF frequency bands, between ship and ship, ship and assigned station or ship station through coast or land mobile station and subscriber.
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37. International telephony network
Coastal radio station
International telephony network
Subscriber
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38. Use of Frequencies Single-side band (SSB) apparatus in radiotelephone stations of the maritime mobile service operating in the bands allocated to this service between kHz and kHz (MF) and in the bands allocated exclusively to this service between kHz and kHz (HF) shall satisfy the technical and operational conditions specified in the relevant ITU Radio Regulations.
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39. Bands between kHz and kHz Frequency 2182 kHz The frequency 2182 kHz is an international distress frequency for radiotelephony. Where administrations provide at their coast stations a watch on kHz for receiving class J3E emissions as well as class A3E and H3E emissions, ship stations may call those coast stations for safety purposes using class H3E or J3E emissions. The frequency kHz may also be used: (a) distress, urgency and safety call and communication; (b) for call and reply; (c) by coast stations to announce the transmission, on another frequency, of traffic lists.
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40. To facilitate use of the frequency kHz for distress purposes, all transmissions on 2182kHz shall be kept to a minimum. Before transmitting on the carrier frequency kHz, a station shall listen on this frequency for a reasonable period to make sure that no distress traffic is being sent; this provision does not however apply to stations in distress.
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41. Bands between 4000 kHz and kHz Call and reply Ship stations may use the following carrier frequencies for calling on RT. frequency ITU channel number 4125 kHz kHz kHz kHz kHz kHz kHz kHz
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42. They are distress and safety frequencies for HF radiotelephony.
Before transmitting on the carrier frequency 4125 kHz, 6215 kHz , 8255 kHz, kHz and kHz, stations should listen on the frequency for a short period to ensure no distress traffic is being sent. However, this provision does not apply to stations in distress.
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43. The ship frequencies above are paired with associated coast station frequencies. Thus coast stations may use the following carrier frequencies for calling and replying to ships on RT. Frequency ITU channel number 4417 kHz kHz kHz kHz kHz kHz kHz kHz
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44. Traffic When using duplex telephony, the transmitting frequencies of the coast station and the corresponding ship station will be in pairs as indicated by appendix 16 of the ITU Radio Regulations. These frequencies may be used by ship stations of any category according to traffic requirements.
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45. duplex telephony (transmitter and receiver can work simultaneously)B
message
Ship A’ transmitter
Ship B’ transmitter
Ship A’ receiver
Ship B’ receiver
One frequency
Another frequency
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46. simplex telephony (transmitter and receiver cannot work simultaneously)B
message
Ship A’ transmitter
Ship B’ transmitter
Ship A’ receiver
Ship B’ receiver
One frequency
Same frequency
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47. VHF bands between 156 MHz and 174 MHz Call and reply Channel 16 (156
VHF bands between 156 MHz and 174 MHz Call and reply Channel 16 ( MHz) is the international channel for distress traffic and for calling on RT in the authorised maritime mobile service VHF bands. The class of emission used for RT on this channel must be G3E. Channel 16 VHF may also be used: (a) distress, urgency and safety call and communication; (b) by coast and ship stations for call and reply; (c) by coast stations to announce the transmission of traffic lists and important maritime information on another channel;
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48. To assist in the reception of distress calls and distress traffic, all transmissions on Channel 16 VHF shall be kept to a minimum and shall not exceed one minute. Also, before transmitting, a station should listen on Channel 16 VHF for a short period to ensure that no distress traffic is being transmitted on this channel. This provision does not apply to stations in distress.
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49. General Procedure for RT The procedures detailed in the following sections are applicable to radiotelephone stations, except in cases of distress, urgency or safety, to which special provisions of the ITU Radio Regulations are applicable. The service of ship radiotelephone stations shall be performed or controlled by an operator holding an appropriate operation certificate recognized by a competent administration.
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50. Station identification Coast stations (a)  by use of a call sign; or (b) by use of the geographical place name as it appears in the List of Coast Stations followed , preferably, by the word RADIO, or same other appropriate indication. Ship stations (a)   by use of a call sign; or (b) by the official name of the ship preceded, if necessary, by the name of the owner on condition that there is no possible confusion with distress, urgency and safety signals; or (c) by its selective call number or MMSI. Ship's survival craft stations (a) by use of a call sign; or (b) a signal of identification consisting of the name of the parent ship follow by two digits.
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51. Method of calling The RT call consists of : (a)  the call sign or other identification of the station called, not more than three times; (b)  the word THIS IS (or DE spoken as DELTA ECHO in case of language difficulties); (c)  the call sign or other identification of the calling station, not more than three times. Example: NITON RADIO NITON RADIO NITON RADIO THIS IS LANDSDOWNE LANDSDOWNE LANDSDOWNE over.
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52. Reply to calls The reply to an RT call consists of: (a) the call sign or other identification of the calling station, not more than three times; (b) the words THIS IS (or DE spoken as DELTA ECHO in case of language difficulties); (c) the call sign or other identification of the called station, not more than three times. (d) over.
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53. Calls from coast stations Coast stations shall so far as practicable, transmit their calls in the form of "traffic lists" consisting of the call signs or other identification in alphabetical order of all ship stations for which they have traffic on hand. The transmission shall be preceded by a general call to all stations. The general call to all stations announcing the traffic lists may be sent on a calling frequency in the following form: • "Hello all ships" or CQ (spoken as CHARLIE QUEBEC) not more than three times; • The words THIS IS (or DE spoken as DELTA ECHO in case of language difficulties); • "Radio" not more than three times • "Listen for my traffic list on ... kHz". Over.
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54. Establishment of RT calls In setting up a radiotelephone call, the coast station should establish connection with the telephone network as quickly as possible. In the meantime, the ship station shall maintain watch on the appropriate working frequency as indicated by the coast station. However, if the connection cannot be established quickly, the coast station shall inform the ship station accordingly. The latter station shall then either: (a) maintain watch on the appropriate frequency until an effective circuit can be established; or (b) contact the coast station later at a mutually agreed time. When a radiotelephone call has been completed, the end of work signal "OUT" should be sent unless further calls are on hand at either station.
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55. Calling 1, establish the communication by call
on the calling frequency or channel
2, determine the working frequency or channel
3, Sending traffic on the working frequency or channel
Calling
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56. Sending traffic Every station should transmit its traffic on one of its working frequencies in the band in which the call has been made. The use of frequencies reserved for calling shall be forbidden for traffic, except distress traffic. After contact has been established on the frequency to be used for traffic, the transmission of a radiotelephone call shall be preceded by: (a) the call sign or other identification of the station called; (b) the words THIS IS (or DE spoken as DELTA ECHO in case of language difficulties); (c) the call sign or other identification of the calling station. The call sign or other identification need not be sent more than once.
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57. In transmitting groups of figures by RT, each figure shall be spoken separately and the transmission of each group or series of groups shall be preceded by the words "in figures". Numbers written in letters shall be spoken as they are written, their transmission being preceded by the words "in letters".
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58. Duration and control of working Calling and signals preparatory to traffic, shall not exceed one minute when made on the carrier frequency 2182 kHz or on Channel 16 VHF, except in cases of distress, urgency or safety. In communications between coast stations and ship stations, the ship station shall comply with the instructions given by the coast station in all questions relating to the order and time of trans­mission, to the choice of frequency, and to the duration and suspension of work. In communications between ship stations, the station called controls the working, i.e. frequency to be used, the duration and suspension of work. However, if a coast station finds it necessary to intervene, the ship stations shall comply with the instructions given by the coast station.
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59. RT tests When it is necessary for a ship station to send signals for testing or adjustments which are liable to interfere with the working of neighbouring coast stations, the consent of these stations shall be obtained before such signals are sent. When it is necessary for a station to make test signals, either for the adjustment of a transmitter before making a call or for the adjustment of a receiver, such signals shall not be continued for more than 10 seconds, and shall include the call sign or other identification of the station emitting the test signals. This call sign or other identification shall be spoken slowly and distinctly. Any signals sent for testing shall be kept to a minimum, particularly on the frequencies for distress and safety purposes.
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60. On board communications Calls for internal communications on board ship shall consist of: From the master station From the sub-station
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61. The management of VHF Often the misuse of VHF channels causes serious interference to essential communications and becomes a potential danger to safety at sea. The proper use of VHF channels at sea makes an important contribution to navigational safety.
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62. a. Channel 16 may only be used for distress, urgency and very brief safety communications and for calling to establish other communications which should then be conducted on a suitable working channel. b. On VHF channels allocated to the port operations service the only messages permitted are restricted to those relating to the operational handling, the movement and safety of ships and, in emergency, to the safety of persons; as the use of these channels for ship-to-ship communications may cause serious interference to communications related to the movement and safety of shipping in congested port areas.
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