Specifications
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3.XBeeZigBeeNetworks
Introduction to ZigBee
ZigBee is an open global standard built on the IEEE 802.15.4 MAC/PHY. ZigBee defines a network
layer above the 802.15.4 layers to support advanced mesh routing capabilities. The ZigBee
specification is developed by a growing consortium of companies that make up the ZigBee
Alliance. The Alliance is made up of over 300 members, including semiconductor, module, stack,
and software developers.
ZigBee Stack Layers
The ZigBee stack consists of several layers including the PHY, MAC, Network, Application Support
Sublayer (APS), and ZigBee Device Objects (ZDO) layers. Technically, an Application Framework
(AF) layer also exists, but will be grouped with the APS layer in remaining discussions. The ZigBee
layers are shown in the figure below.
A description of each layer appears in the following table:
Networking Concepts
Device Types
ZigBee defines three different device types: coordinator, router, and end device.
A coordinator has the following characteristics: it
• Selects a channel and PAN ID (both 64-bit and 16-bit) to start the network
• Can allow routers and end devices to join the network
• Can assist in routing data
• Cannot sleep--should be mains powered.
A router has the following characteristics: it
• Must join a ZigBee PAN before it can transmit, receive, or route data
• After joining, can allow routers and end devices to join the network
ZigBee Layer Description
PHY
Defines the physical operation of the ZigBee device
including receive sensitivity, channel rejection, output
power, number of channels, chip modulation, and
transmission rate specifications. Most ZigBee
applications operate on the 2.4 GHz ISM band at a
250kbps data rate. See the IEEE 802.15.4
specification for details.
MAC
Manages RF data transactions between neighboring
devices (point to point). The MAC includes services
such as transmission retry and acknowledgment
management, and collision avoidance techniques
(CSMA-CA).
Network
Adds routing capabilities that allows RF data packets
to traverse multiple devices (multiple "hops") to route
data from source to destination (peer to peer).
APS (AF)
Application layer that defines various addressing
objects including profiles, clusters, and endpoints.
ZDO
Application layer that provides device and service
discovery features and advanced network
management capabilities.