Sierra Wireless oMG series, Operation And Configuration Manual, Page: 28 / 101

Operation and Configuration Guide 3.14
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5.4.5 Velocity Policy Overview
The Velocity Policy penalizes one link so that others become preferable based on
velocity. It accomplishes this by applying a penalty on a WAN link when the oMG
detects that the vehicle is exceeding a specified speed threshold. This is done to
proactively switch off a link in a managed way prior to the link actually failing,
which would require both the connection and VPN to be re-established.
Since this policy applies a penalty when the defined speed threshold has been
met and continues to penalize the link's score while the threshold is being
exceeded, this policy is typically applied to a WiFi link to facilitate a managed
hand off from that link to a cellular link, such as when leaving a depot.
For example, when applied to a WiFi link, the policy could define a speed
threshold of 20mph so that the vehicle can travel around a depot, utilizing that
link. However, once the vehicle leaves the depot and the speed threshold is met,
the link becomes penalized and another link (e.g. cellular) becomes active.
A key aspect in tuning this policy is to define an appropriate speed threshold such
that the switch from WiFi to cellular happens before WiFi connectively is lost. This
will provide a seamless switch without a drop in connection and will prevent
issues such as having to rebuild a VPN connection which normally occur when a
connection is lost.
In the example of a vehicle leaving a depot, there would likely be a small area of
WiFi coverage outside of the depot, and the vehicle would also likely increase its
speed as it exits the region and travels through this zone. Therefore an
appropriate speed threshold should be chosen to ensure that a switch to cellular
occurs before WiFi connectively is completely lost, thus preventing any drop in
connection during the transition from WiFi to cellular as illustrated here:
Figure 5-12: Setting a Speed Threshold to Switch to Cellular before WiFi Coverage is lost
Note that GPS "jitter" can occur when a vehicle is parked in a location which can
cause the speed threshold(s) defined in the Velocity Policy to be satisfied, thus
resulting in an inadvertent switch in links. It's therefore recommended that a GPS
repeater be installed near the depot to reduce such jitter.
See Velocity Policy on page 65 for a summary of this policy's settings.