XBee®/XBee‐PRO® ZB SMT RF Modules
Coordinator Operation
Forming a Network
The coordinator is responsible for selecting the channel, PAN ID (16-bit and 64-bit), security policy, and stack
profile for a network. Since a coordinator is the only device type that can start a network, each ZigBee network
must have one coordinator. After the coordinator has started 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.
To ensure the coordinator starts on a good channel and unused PAN ID, the coordinator performs a series of
scans to discover any RF activity on different channels (energy scan) and to discover any nearby operating PANs
(PAN scan). The process for selecting the channel and PAN ID are described in the following sections.
Channel Selection
When starting a network, the coordinator must select a "good" channel for the network to operate on. To do
this, it performs an energy scan on multiple channels (frequencies) to detect energy levels on each channel.
Channels with excessive energy levels are removed from its list of potential channels to start on.
PAN ID Selection
After completing the energy scan, the coordinator scans its list of potential channels (remaining channels after
the energy scan) to obtain a list of neighboring PANs. To do this, the coordinator sends a beacon request
(broadcast) transmission on each potential channel. All nearby coordinators and routers (that have already
joined a ZigBee network) will respond to the beacon request by sending a beacon back to the coordinator. The
beacon contains information about the PAN the device is on, including the PAN identifiers (16-bit and 64-bit).
This scan (collecting beacons on the potential channels) is typically called an active scan or PAN scan.
After the coordinator completes the channel and PAN scan, it selects a random channel and unused 16-bit PAN
ID to start on.
Security Policy
The security policy determines which devices are allowed to join the network, and which device(s) can
authenticate joining devices. See chapter 5 for a detailed discussion of various security policies.
Persistent Data
Once a coordinator has started a network, it retains the following information through power cycle or reset
events:
•PAN ID
•Operating channel
•Security policy and frame counter values
•Child table (end device children that are joined to the coordinator).
The coordinator will retain this information indefinitely until it leaves the network. When the coordinator leaves
a network and starts a new network, the previous PAN ID, operating channel, and child table data are lost.
XBee ZB Coordinator Startup
The following commands control the coordinator network formation process.
Network formation commands used by the coordinator to form a network.
Command
Description
ID
Used to determine the 64-bit PAN ID. If set to 0 (default), a random 64-bit PAN ID will be selected.
SC
Determines the scan channels bitmask (up to 16 channels) used by the coordinator when forming a
network. The coordinator will perform an energy scan on all enabled SC channels. It will then perform a
PAN ID scan and then form the network on one of the SC channels.
© 2010 Digi International, Inc.
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DCD [ DIGITAL CORE DESIGN ]
