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Communications Network
Figure 4 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
Figure 4 Inmarsat-C communications network
NCS common channel The NCS has two major functions:
1) Transmitting information on a com-
mon channel.
2) Transmitting EGC messages to MESs.
NCS/LES signalling 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 ex-
changes data between MESs operating
in different ocean regions.