Wavecom W61PC V7.5.0 - Manual (Page 222)

212  Transmission Modes WAVECOM Decoder W61PC/LAN Manual V7.5
In SAT-C TDM mode the MES ID may assume the value 0. This value is interpreted depending on the type
of channel being decoded:
 On a LES TDM channel, MES ID = 0 is interpreted to mean that the MES ID is not known because
the message was not correctly terminated
 On a NCS TDM channel, MES ID is always = 0, since these messages are all EGC messages
SAT-C-TDMA
The SAT-C-TDMA mode includes a frequency memory bar, but no capability to find a traffic-frequency
from a control channel.
For SAT-C-TDMA files are suffixed with '_r' (for “return”).
The MES ID is always = 0, because the ID is not transmitted together with the message as the message
is identified by the Logical Channel Number (LCN).
SAT-C-TDM-EGC
In addition to TDM channel assignments, the NCSC also broadcasts so-called Group Call Messages (En-
hanced Group Calls, EGC), which are not sent to a specific MES, but to groups of MES or to all MES. The
name of the file generated for such a broadcast is suffixed with '_e' (for “EGC”).
Introduction
The Inmarsat C maritime mobile satellite system has an inherent capability, known as Enhanced Group
Call (EGC), which allows broadcast messages to be made to selected groups of ship stations located any-
where within a satellite's coverage. Four geostationary satellites provide worldwide coverage for these
types of broadcasts. Two types of EGC services are available: Safety NET and Fleet NET. Fleet NET is a
commercial messaging services offered by Inmarsat, and is not recognized by the Global Maritime Distress
& Safety System, or GMDSS. Safety NET, along with NAVTEX, is recognized by the GMDSS as the primary
means for disseminating maritime safety information. Ships regulated by the Safety of Life at Sea Conven-
tion travelling outside areas covered by NAVTEX must carry an Inmarsat C Safety NET receiver by 1 Feb-
ruary 1999.
Safety NET Services
Virtually all navigatable waters of the world are covered by Inmarsat satellites. Each satellite transmits
EGC traffic on a designated channel at 1.5 GHz. Any ship sailing within the coverage area of an Inmarsat
satellite will be able to receive all Safety NET messages broadcast over this channel by that satellite. All
Inmarsat C maritime ship stations can monitor the EGC channel. The EGC channel can also be monitored
by dedicated receive-only equipment installed separately or as part of an Inmarsat A station.
The International Maritime Organization has announced that by June 1998, broadcasts of navigational and
meteorological information will be made for every NAV/MET Area of the globe. Search and Rescue infor-
mation is also broadcast in most areas.
Inmarsat C Safety NET services currently include:
 Urgency messages and navigational warnings to rectangular or circular areas
 Coastal warnings (in place of NAVTEX; used only in Australia)
 Shore-to-ship distress alerts to circular areas
 Search-and-rescue coordination messages to rectangular or circular areas
 Meteorological and navigational warnings and meteorological forecasts to a NAVAREA
 United States Safety NET broadcasts include:
 NAVAREA IV and XII navigational warning broadcasts from the U.S. National Imagery and Mapping
Agency
 NAVAREA IV, XII and XVI meteorological forecasts and warnings from the U.S. National Weather
Service
 Distress alerts and search and rescue warnings from the U.S. Coast Guard
 Atlantic ice reports from the International Ice Patrol, U.S. Coast Guard