G-4 Saturn B – Chapter 5. Appendices
ROM Read-Only Memory, microchip memory that stores fixed pro-
grams.
Rx Receive.
SAR Search And Rescue, organisations that perform search and
rescue at sea; usually have land base that often is interconnected to
Inmarsat systems.
SCC Satellite Control Centre
SCPC Single Channel per Carrier
SDM (Inmarsat) System Definition Manual
Spot Beam (Inmarsat-B) service that divides each Ocean Region into
sub-regions, each “spotlighted” by a beam from the region satellite;
permits increasing capacity of system.
SU Signalling Unit, 96-bit data packets used to conduct user-to-user
system signalling.
TDM Time Division Multiplexing, method of allowing several users to
share the same channel.
TDMA Time Division Multiple Access
Terrestrial Network a fixed telecommunications network, such as a
telephone network or a data network, which connects to the Inmarsat-
B system at an LES/NCS.
TUP Telephone User Part of CCITT Signalling System No 7.
Tx Transmit
Uplink radio link from a station on Earth up to the satellite.
UTC Coordinated Universal Time, referenced to Greenwich Mean
Time (GMT)
UW Unique Word
WMO World Meteorological Organization
X.25 type of data network protocol, known as message switched, as
messages are transferred in packets.
X.400 type of data network protocol, known as message switches as
entire messages are compiled and transmitted as units; includes
services such as electronic mail.
List of Terms Cont’d
Appendix G – List of Terms Cont’d
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