Table of Contents
Advertisement
www.agelectronica.com
3. ZigBee Networks
3.1. ZigBee Network Formation
3.1.1. Starting a ZigBee Coordinator
3.1.2. Joining a Router
www.agelectronica.com
A ZigBee Personal Area Network (PAN) consists of one coordinator and one or more routers and/or
end devices. A ZigBee Personal Area Network (PAN) is created when a coordinator selects a
channel and PAN ID to start on. Once the coordinator has started a PAN, it can allow router and
end device nodes to join the PAN.
When a router or end device joins a PAN, it receives a 16-bit network address and can transmit
data to or receive data from other devices in the PAN. Routers and the coordinator can allow other
devices to join the PAN, and can assist in sending data through the network to ensure data is
routed correctly to the intended recipient device. When a router or coordinator allows an end
device to join the PAN, the end device that joined becomes a child of the router or coordinator that
allowed the join.
End devices, however can transmit or receive data but cannot route data from one node to
another, nor can they allow devices to join the PAN. End devices must always communicate
directly to the parent they joined to. The parent router or coordinator can route data on behalf of
an end device child to ensure it reaches the correct destination. End devices are intended to be
battery powered and can support low power modes.
Figure 3‐01. Node Types / Sample of a Basic ZigBee Network Topology
The network address of the PAN coordinator is always 0. When a router joins a PAN, it can also
allow other routers and end devices to join to it. Joining establishes a parent/child relationship
between two nodes. The node that allowed the join is the parent, and the node that joined is the
child. The parent/child relationship is not necessary for routing data.
When a coordinator first comes up, it performs an energy scan on multiple channels (frequencies)
to select an unused channel to start the PAN. After removing channels with high detected energy
levels, the coordinator issues an 802.15.4 beacon request command on the remaining, low energy
level channels. Nearby routers or coordinators that have already joined a PAN respond to the
beacon request frame with a small beacon transmission indicating the PAN identifier (PAN ID) that
they are operating on, and whether or not they are allowing joining. The coordinator will attempt
to start on an unused PAN ID and channel. After starting, the coordinator may allow other devices
to join its PAN.
When a router first comes up, it must locate and join a ZigBee PAN. To do this, it issues an
802.15.4 beacon request command on multiple channels to locate nearby PANs. Nearby routers
and coordinators that have already joined a PAN respond to the beacon request frame with a small
beacon transmission, indicating which channel and PAN ID they are operating on. The router
listens on each channel for these beacon frames. If a valid PAN is found from one of the received
beacons, the router issues a join request to the device that sent the beacon. If joining succeeds,
the router will then receive a join confirmation from the device, indicating the join was successful.
© 2007 Digi International, Inc.
www.agelectronica.com
17
www.agelectronica.com
Advertisement
Table of Contents
