Communications Network - Furuno FELCOM 12 Service Manual

1.3 Communications Network

The illustration below shows the Inmarsat-C network.
2
Data landlines
Telex landlines
Landlines
8
1) NCS commom channel
This channel is transmitted continuously (24 hours/day) by the NCS. All SESs must be
tuned to the NCS common channel when not engaged in message transfer. Its main
functions are;
a. shore-to-ship message announcements
b. ship-to-shore message announcements
c. polling commands
d. EGC message transmission
e. login and logout acknowledgement
2) NCS/CES signalling link
This is the link between an NCS and all LESs in its region. Its functions are;
a. establishing initial signalling link between CES and NCS to transmit via the NCS
common channel
b. forwarding EGC message to NCS
c. forwarding NCS received distress alerts to LES.
3) CES TDM channel
This channel carries all signalling and message traffic to the SESs concerned with
message transfer with a particular LES.
NCS/CES
Signalling Link
SES Signalling
5
Channel
Land Earth
Station
SES Message
4
(LES) or
Channel
Coast Earth
Station
CES TDM
3
(CES)
Channel
NCS/NCS
6
Network
Signalling Channel
Coordination
Station (NCS)
NCS Common Channel
1
Data Circuit
Terminating
Equipment
(DCE)
1-7
Mobile Earth Station (MES)
Data Terminal
Equipment (DTE)
7
EGC Received