Sierra Wireless AirLink MP890, User Manual

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Introducing the MP Modem
Rev 1.0 Mar.10 11
GRE
GRE (Generic Routing Encapsulation) tunnel is used to carry non-IP packets
through an IP Network. Non -IP packets, that are send over the GRE tunnel, need
to be first encapsulated. Hence, ALEOS is used to configure and encapsulate
non-IP packets and transmit over IP through the GRE tunnel.
Applications
Events Reporting
Events Reporting is Sierra Wireless AirLink’s modem’s new software feature
provided via ACEmanager and Ace View, that allows the users to generate
reports from the events that take place. Event Reporting Protocol is an intuitive
embedded protocol, which automatically formats the messages based on an
event trigger. The messages generated are then reported to the remote server.
GPS
The Global Positioning System (GPS) is a satellite navigation system used for
determining a location and providing a highly accurate time reference almost
anywhere on Earth. The US military refers to GPS as Navigation Signal Timing
and Ranging Global Positioning System (NAVSTAR GPS).
GPS consists of a “constellation” of at least 24 satellites in 6 orbital planes. Each
satellite circles the Earth twice every day at an altitude of 20,200 kilometers
(12,600 miles). Each satellite is equipped with an atomic clock and constantly
broadcasts the time, according to its own clock, along with administrative
information including the orbital elements of its motion, as determined by ground-
based observatories.
A GPS receiver, such as the MP, requires signals from four or more satellites in
order to determine its own latitude, longitude, and elevation. Using time synced to
the satellite system, the receiver computes the distance to each satellite from the
difference between local time and the time the satellite signals were sent (this
distance is called psuedoorange). The locations of the satellites are decoded
from their radio signals and a database internal to the receiver. This process
yields the location of the receiver. Getting positioning information from fewer than
four satellites, using imprecise time, using satellites too closely positioned
together, or using satellites too close to the Earth’s curve will yield inaccurate
data.
The GPS data is then transmitted to a central location which uses a tracking
application to compile information about location, movement rates, and other
pertinent data.
Note: Depending on the location of the satellites in relation to the modem’s location and
how many signals are being received, the MP may encounter “GPS drift”. The MP may
report it is in a location a few feet from its actual location because it does not employ differ-
ential GPS.