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1.2 Inmarsat C Services
The Inmarsat C system provides the following communication services. That is, all LESs
supports these services.
(1)Store-and-forward Telex message service
(2)EGC (Enhanced Group Call) broadcasting
(3)Distress alerting and safety services
The following services are also available if supported by the CES selected.
• Ship-to-shore half duplex communication
• Full duplex communication
• Polling: Individual polling, Group polling, Area polling
(The facility whereby an operational center sends an instruction to selected MES, to
perform a defined task, such as return a pre-assigned data report.)
• Data reporting
(Data report, such as ship's position is sent regularly to a terrestrial subscriber.)
• EGC Fleet NET
TM
service (Commercial service)
1) Store-and-forward Telex service
In the store-and-forward techniqne, data that is to be transmitted is converted into digital
form, and sent in data packets over the satellite link, to be stored and subsequently
forwarded to the called party when traffic loading permits.
The following briefly describes how a MES sends a ship-to-shore message.
The MES operator prepares the message in the text editor. The MES stores the message
in its DTE, ready to pass it to the DCE for transmission.
The DCE transmits a channel assigment request to LES.
After receiving a channel assigment, the DCE starts transmitting the message in packets.
The LES checks the receivied packets for errors, and if it finds any, returns an
acknowlegement packets identifying the packets in error.
The CES receives all the data packets with no errors, and forwards the message via
public network to the intended desitination.
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