What are Radio telephony Procedures as per GMDSS?

Duplex and simplex mode of R/T operation.

• Simplex operation is used for :-
  1. All stations broad cast, distress urgency, safety and    routine call and reply.
  2. Ship to ship communication.

Note :-

In simplex mode one frequency is used for transmission and reception. ex :- CH – 16 2182 kHz.

• Duplex operation used for :-
  • Ship to coast station. (CRS)
  • Public correspondence using paired frequency.

Note :-

In Duplex mode transmission and reception are simultaneous using two different frequency so that it is just like normal telephonic conversation.

Points to remember:-

Radio telephone calls, may also be made on semi – simplex/ duplex mode where one end uses simplex and other end uses duplex.

Calling procedure :-

Once the chosen frequency is established, the ship station operator should ensure that proceeding with the call is not likely to cause interference to transmission already in progress. If by chance interference is there, transmission must be ceased.

Incomplete call :-

When a station receives a call without being certain for which call is intended, it shall not reply until call has been repeated.Alternatively, if the call is intended for it but the called station is uncertain who is calling, it shall reply immediately, asking for repetition.

Example :-

Station call  M.T. SMITI please repeat your call over.

Calls to coast station :-

• Calls made on the appropriate working channel whenever possible as indicated in ITU list of coast station or ALRS – Vol-1.
• If working channel is not available then 2182 kHz (MF) or ch-16 (VHF) may be used for primary calling.
• When making a call to coast station on 2182 kHz, the ship station operator should indicate the reason for call and intended working frequency/ channel for subsquent traffic.
• If a CRS in called on the working frequency/ channel, it should normally reply on the same or paired frequency / channel on the same band.
• When calling on VHF working channel the ship stations should indicate channel being used.

Control of traffic :-

• During communications between ships and coast stations the coast station control the working.
• In communications between ships, the called ship stations control the working.
• However if a CRS finds it necessary to intervence in communication between ships, both ship station should abide by instruction from CRS.

Release of Identification:-

1. A station should release its identification at the beginning and end of the transmission.
2. Afterwards as frequent as necessary.
3. In case of long communication, identification should be release at least every 15 minutes.