32 AVR2070 8240B-AVR-06/09
8. Some pre-deployment configuration can be used to determine whether a
given node should or can join a given network. This configuration is part of
the application, not the MAC.
9. Only short (16-bit) 802.15.4 addresses are used in sending data over the
network except during association, since a new node does not have a short
address until it is issued one.
10. The coordinator's short address is defined to be 0x0000.
A.4 Implementation Details A.4.1 End node
The message sequence chart in Figure A-4-1 shows the effect of the end node
“scanning” a particular channel by sending out a beacon request and receiving a
beacon.
Figure A-4-1 Channel Scan Message Sequence
End/Router Node Pan Coord/Router Node
Beacon Request
Beacon
When the end node powers up, it performs a scan to find a parent node.
The node sends a beacon request frame on each channel and listens for beacon
frames. The node picks a router based on the following criteria:
1. Pick the router/coordinator with the highest LQI value for the link.
2. In event of a tie with LQI, pick the router/coordinator with the lowest number
of hops to a coordinator.
3. In event of a tie with hops, pick the highest RSSI value for the link.
Note:
If the compile flag DEMO is set, these criteria above are altered to only
find the best RSSI during association. This provides a mechanism to
demonstrate multi-hop routing.