Narrow Band Direct Printing (NBDP)

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Overview

Narrow Band Direct Printing (NBDP) telegraphy is a means of communication whereby a printed or hard copy is available at each communications terminal. NBDP is also known as radiotelex, and is used for MSI broadcasts.

Performance standards, testing standard & carriage requirement

Carriage requirement

NBDP is required for sea area A2 as per SOLAS chapter IV, regulation 9.3.1. However SOLAS chapter IV, regulation 9.3, permits that the requirement of having NBDP can be fulfilled by providing an additional Inmarsat ship earth station.

NBDP has been removed as a requirement in the Modernization of the GMDSS.

Performance Standards

  • Resolution A.806(19) amended by MSC.68(68)

Testing Standard

  • IEC 61097-9

How it works

In simple terms, NBDP (Narrow Band Direct Printing) is a telex; a way to communicate with text rather than by voice.

It is said that NBDP was introduced in the GMDSS to help seafarers whose first language was not English. They did not have to speak to broadcast their distress message, instead they could type and send.

NBDP uses narrow band width for transmitting the message. When a message is received, it prints the message on the screen and on the printer connected with NBDP.

  • NBDP can send and receive text messages with to and from a single station
  • NBDP can transmit text message stored in the equipment (SD card or floppy)
  • NBDP can broadcast a message to all the stations that have their NBDP tuned in to the frequency on which message is transmitted

ARQ and FEC modes

These are two modes of transmission for NBDP.

ARQ Mode

ARQ mode is used for one to one communication. For example when a ship wishes to communicate with a specific ship or coast station.

With ARQ mode:

  • you send an information (text) when you are transmitting station
  • you press Over key (F9) and you become receiving station; you now can read the message what other station is sending
  • when the other station presses “Over”, you again become the transmitting station and this process goes on.

FEC Mode

FEC (Forward error correction) mode is for one station to one or many stations. This mode is used for broadcasting the message. For example if a ship need to broadcast a distress telex message, FEC mode should be used.

Unlike ARQ mode, FEC is only one way. That is, with FEC we can transmit our message and then end the communication.

With FEC mode:

  • you send the information you wish to send
  • once the information is sent, you disconnect the connection
  • you cannot switch between transmission and receiving mode

So if you want to communicate with other station, you need to choose ARQ mode. But if you just want to transmit your message, you can choose FEC mode.

So when transmitting a distress message to all station through NBDP, you must use FEC mode.

See also

References

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