3. XBee ZigBee Networks
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:
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)
ZDO
Application layer that defines various addressing objects including
profiles, clusters, and endpoints.
Application layer that provides device and service discovery features and
advanced network management capabilities.
Networking Concepts
Device Types
ZigBee defines three different device types: coordinator, router, and end device.
Node Types / Sample of a Basic ZigBee Network Topology
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
•Can buffer RF data packets for sleeping end device children.
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