Image Processing Reference
In-Depth Information
support for a shared time base, security improvements. GTS support was made optional and more
flexibility in the CSMA-CA algorithm was provided.
29.5.5.2 ZigBee
ZigBee [] adds a network layer enabling self-forming and self-healing mesh networks. For this
purpose, it provides appropriate routing services including route discovery and maintenance. It also
includes mechanisms for starting, joining, and leaving a network.
Within the ZigBee application layer, the so-called application support sublayer (APS) provides
the interface to the network layer. It consists of the APS Data Entity, which provides services for data
exchange, and the APS Management Entity, which hosts services for binding and group management.
The services of the APS are used by the so-called application objects (AOs), which actually imple-
ment the device application. Each AO forms an independent functional subunit and can be addressed
via its endpoint number. A ZigBee device may host up to of them.
The ZigBee Device Object (ZDO) is a special AO residing at endpoint in every ZigBee device.
It implements the server entities required for device and network management, for use by both
local and remote clients. hese include device and service discovery, (self) description, joining net-
works, binding management, and configuration of security services (e.g., key establishment and
authentication).
The communication endpoints of AOs are called
clusters.
hestructureoftheAOsaswellastheir
clusters is not defined by the core protocol specification. Interoperability between ZigBee devices is
enabled by
application proiles,
which define the semantics of messages exchanged between clusters.
∗
Application profiles are each dedicated to a specific application domain. hey can be manufacturer
speciicorpublic.Atthetimeofwriting,theHomeAutomationproileistheonlyonepublished,
although more have been announced.
Device descriptions
within an application profile specify the clusters that have to be present in a
particular AO (and thus, physical device). Examples from the Home Automation profile are
On/Off,
Light
,
On/Off Light Switch
,and
Pump
.
The ZigBee Cluster Library (which is separate from the core protocol specification) predefines a
variety of clusters for use by application profiles. It specifies clusters as collections of commands and
attributes, following a client-server pattern. While a single attribute of a cluster represents a single
datapointtobecontrolled(e.g.,thestateofalight),commandsareusedtomanipulatetheseattributes
as well as to initiate actions within the device. In addition, mechanisms for attribute discovery and
change reporting (according to defineable criteria) are deined. he cluster library also contains basic
data type definitions (e.g., Integer and String). As an example, the
On/Of Light
device from the Home
Automation profile contains the (mandatory) server clusters
On/Off,
,
Scenes
,and
Groups
,andthe
optional client cluster
Occupancy Sensing
from the cluster library.
ZigBee security is based on the mechanisms specified in IEEE .., but extends them by intro-
ducing different keys for end-to-end and network wide security. It also provides mechanisms for key
distribution.
The ZigBee standard was first published in . The release added features such as device
groups and multicast, but was not compatible with the original specification. It also removed the
original key-value-pair service in favor of the cluster library. The standard update released in
maintains compatibility with ZigBee , adding optional mechanisms for avoiding radio channels
with strong interference (frequency agility) and fragmentation. In addition, the “ZigBee-PRO” stack
profile offers more features, but only limited compatibility, and has a larger memory footprint.
∗
In addition, they define network parameters that need to be aligned, such as preferred channels.
