Here we will look at the different operating modes, calling methods and established calling procedures. In addition, we will decipher international telex service codes and eliminate potential causes of ineffective calls, allowing you to effectively resolve communication problems.
While largely superseded by modern technologies like email and satellite communication, maritime telex remains a crucial element of the Global Maritime Distress and Safety System (GMDSS). This ensures continued communication capabilities even in remote areas or during emergencies.
Maritime Telex Operation
This section covers MF and HF telex procedures. NBDP means Narrow Band Direct Printing and is used for marine telex transmissions. Sometimes this is also known as direct-printing telegraphy.
Modes of Operation
Three modes of operation are used dependant upon the message destination, i. e., whether the message is addressed to one specific station or to all stations:
ARQ Mode – For communication between two stations. In this mode the receiving telex checks the incoming code groups representing the first three characters and if these are correct it requests the sending telex to send the next three characters. If a group is received incorrectly, the receiving telex requests a repeat of the last group, i. e., ARQ = Automatic request for repeat.
FEC Mode – For communications to “All Stations“. Sometimes known as Broadcast FEC (B-FEC), or collective FEC. This mode would be used, for example, for distress traffic or for NAVTEX broadcasts. The information is sent continuously with a continuous repeat five characters later, i. e., FEC = Forward Error Correction. The receiving telex waits for each repeated character and, providing one of the two characters conforms to the correct code, the character is printed.
SELFEC Mode – Used for transmission from one station to another, specific, station. Similar in operation to B-FEC but normally used by a coast station to transmit to a ship in port whose transmitter is not available. SELFEC = SELective FEC.
Calling Techniques
Telex calls to coast station can be made manually by entering the station’s SELCALL number, e. g., 3220 for UK, and then entering manually the transmit and receive frequencies. In some units it is possible to enter the ITU channel number for HF operation.
When communication has been established, various command codes can be used dependant upon the purpose of the call or the service required. An example is shown later of a direct telex call to a shore-based subscriber.
Fully automatic calls can also be made in which the operator selects first the coast station, from a pre-programmed list; next the required message for transmission time. The equipment then the transmission time. The equipment then chooses the most appropriate free channel and sends the message.
With modern telex terminals it is usual to program in the stations with which the ship is likely communicate so that the required station can be simply selected from a list. Similarly, the station’s frequencies are also stored and the equipment may recommend an appropriate frequency, depending upon time of day and upon the signal path. Individual manufacturer’s manuals should be consulted for further details.
If possible, the message should be prepared in advance, either by pre-punching a paper tape or by typing the message into memory, with the telex terminal in local mode. This allows editing of the message before transmission. The modern type of telex terminal with VDU and electronic memory can provide excellent editing facilities but, previously, the very limited medium of punched paper tape had to be used to prepare, store and telex messages.
The telex message format should generally include the following information:
- the destination company and/or name of the addressee;
- the name and title of the message originator;
- a message reference number and/or the subject of the call;
- the text of the message.
Part of good communication technique is to choose the best time to make telex calls, wherever possible, considering the following factors:
- avoidance of congestion by calling outside peak hours;
- the local time difference between the ship and the called subscriber, in order to avoid inconvenience and delay.
Calling Procedure
To establish communications with a coast station, use the following procedure:
- Select paired frequency channels, using the ITU List of Coast Stations or appropriate nationally recommended publications (some stations emit channel free signal in A1A/F1B mode when channel is idle, such as their call sign in Morse code followed by a telex signal).
- Key in the coast station SELCALL number, e. g., 3220.
- Initiate the NBDP call in ARQ mode. If your call is accepted, you should receive the station’s answerback, e. g., Portishead Radio has answerback 3220 Auto G.
- Send the ship station’s answerback (often this done automatically ). An example of a ship station answerback is 45656 GBLW X.
The ship then receives, for example, an indication of whether or not there is traffic held for it at the coast station, followed by the invitation – sent as the code GA+? – to “GO AHEAD” with the communication.
Once communication has been established, the services provided by the coast station may be accessed by sending the command code for the service required.
A list of standard command codes is given in Table 1.
Table 1. Telex command codes | |
---|---|
COD | DESCRIERE |
AMV | Message to be sent to AMVER (see section “NON-DSC Terrestrial Distress CommunicationsNBDP Acknowledgement“) |
BRK | Radio path to be immediately disconnected |
DATA [number] | Message to be forwarded by the coast station, using data facilities, to the PSTN subscriber number indicated |
DIRTLX [number] | Direct telex connection to the indicated telex subscriber number is required |
FAX [number] | Message to be forwarded as facsimile, via the PSTN, to the subscriber telephone number indicated |
FREQ | Message contains the frequency on which the ship is keeping watch |
HELP | List of the available system facilities is required immediately |
INF | Information is immediately required from the coast station’s database |
KKKK | Network connection should be cleared whilst maintaining the radio path; further messages/communications should follow immediately |
MAN | Message is to be stored and forwarded manually to a country where an automatic telex connection is not available |
MED | An URGENT medical message follows |
MSG | Message held by the coast station need to be sent immediately |
MULTLX [number1] [number 2] | Direct telex connection to multiple (i. e., at least 2) telex numbers is required |
MULTLXA | As MULTLX, but advice of delivery also required |
NAV | Current navigational warning messages required |
OBS | Meteorological message to be sent to the appropriate meteorological organization(s) |
OPR | Connection through a manual assistance operator required |
POS | Message contains the ship’s position: assists automatic transmission and reception of messages by the coast station, e. g., for selection of optimum traffic frequency (see page “Exploring Radio Paths, Spectrum, and Propagation MechanismsFrequency bands and propagation“) and directional antennas |
RDL | Redial the last telex number indicated by DIRTLX |
RPT [identifier] | Retransmission of an earlier broadcast message, sent in FEC mode, is required in ARQ mode; the specific message must be referenced using the appropriate message identifier |
RTL | Message is to be forwarded as a radio telex letter |
STA | Ship station requires an immediate status report of the store-and-forward messages it has sent; individual messages may be referenced by adding the appropriate message identifier |
STS [SELCALL/MMSI] | Message is to sent via the coast station store-and-forward facility to a specific ship identifier by a SELCALL or MMSI number |
SVC | Service message intended for subsequent manual attention |
TEL [number] | Message to be relayed by voice from the coast station to the telephone number indicated |
TGM | Message to be forwarded as a radio telegram |
TLX [number] | Message is for immediate connection to a store-and-forward facility at the coast station |
TLXA [number] | Is TLX, but with advice of delivery to the indicated telex number using normal shore-to-ship procedures |
TRF | Information on current tariff applied by the coast station is required (automatic service only) |
TST | A test message text (e. g., “the quick brown fox jumps over the lazy dog”) is required (automatic service only) |
URG | Emergency use only: the ship station needs to be connected to a manual assistance operator urgently (an audible alarm may be activated at the coast station) |
VBTLX [number] | Message is to be dictated by the coast station to a voicebank (voice messaging) telephone number for subsequent retrieval by the addressee and duplicated by telex to the telex subscriber number following the command code; the telephone number of the voicebank telephone is included in the first line of the message text of the message |
WX | Weather information is required immediately |
For example, a telex connection to a distant shore-based subscriber would use the command code:
e. g.,
where:
- 065 = the telex country code for Romania;
- 426358 = the called subscriber’s national telex number;
- + = character that terminates the telex number and initiate the call.
After an exchange of answerbacks, and upon receipt of the “MESSAGE” code MSG+, the ship sends its traffic. Usually, previously prepared messages will be selected for transmission by following the instructions on the telex VDU screen or, on some older terminals, by using the punched paper tape reader. However, it is also possible to type in messages directly from the keyboard.
To disconnect the circuit to the shore-based subscriber, the operator should key in code KKKK. The coast station should then respond with a date/time group and call duration, followed by an invitation to continue, i. e., GA+?
To close the link with the coast station, the operator should key in the code BRK+ and return the telex terminal to the “STANDBY” condition.
International Telex Service Codes
A list of facility codes and abbreviations is show in the ITU List of Coast Stations and other publications produced by national administration and service providers. The more commonly used codes are show in Table 2.
Table 2. International Telex Service codes and abbreviations | |
---|---|
COD | DESCRIERE |
ABS | Subscriber absent/Equipment off |
ADD | Please input your international telex number |
ANUL | Delete |
BCT | Broadcast call |
BK | Break (I cut off) |
BMC | End of message/transmission not receive; message cancelled |
CFM | Please confirm/I confirm |
COL | Collate please/I collate (repetition of, for example, figures, mixed figures or sensitive/important information) |
CRV | Do you receive well?/I receive well |
DER | Out of order |
DF | You are in communication with the called subscriber |
EXM | Connection cleared down (cut off) because paper/tape/other recording |
FMT | Format error |
GA | Go ahead |
IAB | Invalid answerback received from called party |
IMA | Input message acknowledgement |
INF | Called subscriber temporarily unobtainable; call the information service |
ITD | Input transaction accepted for delivery |
ITL | I transmit later |
JDE | Office closed because of holiday |
LDE | Maximum acceptable duration or length of the message has been exceeded |
MNS | Minutes |
MOM | Wait/Waiting (a moment) |
MUT | Message mutilated |
NA | Correspondence with this subscriber is not admitted |
NC | No circuits |
NCH | Called subscriber number changed |
NDN | Non-delivery notification |
NI | No line identification available |
NP | The called party is not, or is no longer, a subscriber |
NR | Indicate your call number/My call number is |
OCC | Called subscriber is engaged (occupied) |
OK | Agreed/Do you agree |
PPR | Paper |
R | Received |
RAP | I shall call you back |
RDI | Redirected call |
REF | Reference of the delivered telex message generated by a message conversion facility (CF) for telex-teletex interworking |
REI | Address validation failure/non-compliant answerback received |
RPT | Repeat/I repeat |
RSBA | Retransmission being attempted |
SSSS | Change of alphabet |
SVP | Please (s’il vous plait) |
T or 5 | Stop your transmission! (Repeated until effective) |
TAX | What is the charge?/The charge is |
TEXT MSG | Please send a text message |
THRU | You are in communication with a telex position |
TMA | Maximum number of addresses exceeded |
TPR | Teleprinter |
TTX | Designation of the conversion facility (CF) for telex- teletex interworking |
VAL | Validation response |
W | Words |
WRU | Who is there/Who are you? |
XXXXX | Error |
Ineffective Calls
In the event of an ineffective call attempt when calling from a manual terminal, a non-delivery service signal code will be returned with the meaning stated in Table 2. The operator needs to consider this information in order to determine how best to proceed.
If OCC or NC are returned then the difficulty may be assumed to be temporary and the call should be attempted again after waiting for a minute or so.
Read also: Exploring Radio Paths, Spectrum, and Propagation Mechanisms
A longer wait of at least 5 minutes will be necessary if, as indicated by the code DER, the called subscriber’s terminal is shown as “out of order“. The problem at the distant terminal may be relatively minor, e. g., paper or ribbon being replaced, and therefore soon remedied. However, if subsequent calls still fail then the problem is more serious and the Telex Enquiry Service should be informed.
If any of the service signal codes ABS, NA, NP or NCH are returned, the first step should be re-check the subscriber’s number and try again. If the same service signal is returned again, the problem should be referred to the Telex Enquiry Service since it is unlikely to be cleared quickly.