Specifications
XBee®/XBee‐PRO®SERFModules
©2009DigiInternational,Inc. 29
4. The Associate LED will start blinking once the coordinator has selected a channel and PAN ID.
5. The API Modem Status frame ("Coordinator Started") is sent out the UART (API firmware only).
6. Reading the AI command (association status) will return a value of 0, indicating a successful
startup.
7. Reading the MY command (16-bit address) will return a value of 0, the ZigBee-defined 16-bit
address of the coordinator.
After startup, the coordinator will allow joining based on its NJ value.
Router Operation
Routers must discover and join a valid ZigBee network before they can participate in a ZigBee
network. After a router has joined a network, it can allow new devices to join the network. It can
also route data packets and communicate with other devices on the network.
Discovering ZigBee Networks
To discover nearby ZigBee networks, the router performs a PAN (or active) scan, just like the
coordinator does when it starts a network. During the PAN scan, the router sends a beacon
request (broadcast) transmission on the first channel in its scan channels list. All nearby
coordinators and routers operating on that channel (that are already part of a ZigBee network)
respond to the beacon request by sending a beacon back to the router. The beacon contains
information about the PAN the nearby device is on, including the PAN identifier (PAN ID), and
whether or not joining is allowed. The router evaluates each beacon received on the channel to
determine if a valid PAN is found. A router considers a PAN to be valid if the PAN:
• Has a valid 64-bit PAN ID (PAN ID matches ID if ID > 0)
• Has the correct stack profile (ZS command)
• Is allowing joining.
If a valid PAN is not found, the router performs the PAN scan on the next channel in its scan
channels list and continues scanning until a valid network is found, or until all channels have been
scanned. If all channels have been scanned and a valid PAN was not discovered, all channels will
be scanned again.
In the smart energy profile, devices cannot attempt joining repeatedly. To be compliant to smart
energy requirements, the XBee performs up to three channel scans. If all three attempts fail, the
application or user must retry joining. The following events cause the XBee to perform up to three
join attempts:
• Single commissioning button press (see chapter 7)
• CB command with a parameter of 1
• Resetting the XBee (FR or hardware reset).
Joining a Network
Once the router discovers a valid network, it sends an association request to the device that sent a
valid beacon requesting a join on the ZigBee network. The device allowing the join then sends an
association response frame that either allows or denies the join.
When a router joins a network, it receives a 16-bit address from the device that allowed the join.
The 16-bit address is randomly selected by the device that allowed the join.
After joining a network, the router sends a broadcast ZDO device announce message advertising
its 64-bit and 16-bit addresses.
Authentication
In a smart energy network, the router must then go through an authentication process. See the
Security chapter for a discussion on security and authentication.
After the router is joined (and authenticated, in a secure network), it can allow new devices to join
the network.