FELCOM 16

INMARSAT C SYSTEM
Communications Network
The illustration below shows the Inmarsat C communications network.
NCS/LES
Signaling Link
Network
Coordination
Station (NCS)
NCS/NCS Signaling Link
NCS Common Channel
Data
Communications
Network
Telex Network
Land Earth
Station
(LES)
Terrestrial
Communications
Network
MES Signaling
Channel
MES Message
Channel
LES TDM
Channel
Data Circuit
Terminating
Equipment
(DCE)
Mobile Earth
Station (MES)
Data Terminal
Equipment (DTE)
Enhanced Group
Calling (EGC) Receiver
Inmarsat C communications network
NCS common channel
NCS/LES signaling link
LES TDM channel
MES message channel
MES signaling channel
NCS/NCS signaling link
MES interface
Terrestrial network
interface
The NCS has two major functions:
1) Transmitting information on a common channel.
2) Transmitting EGC messages to MESs.
This is the link between NCS and all LESs in its
region. All EGC messages pass through this link.
This channel carries the circuit control signal for
MES and transmits messages from LES to MES.
This channel carries messages from MES to LES.
This channel transmits requests, data reports, etc. In
addition, it carries login and logout from MES to
NCS.
This is the link between NCSs. It exchanges data
between MESs operating in different ocean regions.
The MES consists of the Data Circuit Terminating
Equipment (DCE) and the Data Terminal Equipment
(DTE). The DCE consists of the antenna unit, and
the DTE consists of the communications unit and
terminal unit (PC).
The major functions of the LESs are:
1) Telex store-and-forward conversion
2) Handling EGC messages
3) Data Reporting and Polling
4) Distress message processing
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