pulsAR
radio Operator's Manual
3. Connectivity to a central site, through a backbone network, is maintained when a mobile changes
parent. Packet routing is switched over autonomously throughout the network so that packets are
correctly routed immediately after the mobile radio changes the access point.
4. Using the Tree topology you can use the fixed nodes in the tree (root and branches) to provide the
backbone network. Those same radios can also be the access points to the mobile leaf nodes.
This approach depicted in Figure 2.3.
Each roaming radio decides on its own when to switch to another access point. If the signal strength
from the current parent drops down to a point where the link performance becomes compromised,
and
there is a stronger signal from an alternate access point, then the mobile radio drops its current
link and reattaches to a stronger parent. Once it reattaches to the network, the roaming radio
broadcasts its new position so that all the equipment in the network will update their routing tables
accordingly. Overall the switch-over takes less than 150 ms.
The roaming feature is very flexible and can be used to address several different applications as
explained below. The last two do not even involve mobile nodes.
2.2.2
Roaming branches
Branch nodes can also be configured to roam. This is useful in a mobile environment where each
moving platform can be the access point for other mobile platforms. In this environment the network
topology changes and adapts automatically to keep all nodes connected with strong links and minimal
number of hops to the root. You can have up to seven moving access points without creating any
interference (you can have more with careful selection of channels). Refer to the last example in
appendix E for the setup of a mobile network where multiple mobile radios serve as access points.
2.2.3
Fast roaming
In the default mode each roaming radio scans for an alternate access point every 640 ms (or twice that
if you set the TDD cycle period to 40 ms). If there are many different channels to scan (up to 12 for
leaf nodes), the assessment of the complete environment could take upwards of 10 seconds. This is
acceptable for most applications where the RF environment does not change abruptly. But if the
vehicles move very fast
and
are set to scan many channels, you may want to set the
roam speed
to
2-6
Figure 2.3 - Roaming vehicles attaching to any of three access points
hub 2
f2
hub 3
f3
.
Control center
root-1
f1
Summary of Contents for AR-24010E
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