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