Developing Practical Wireless Applications

ZigBee: Untethered and Unlicensed 173

Chapter 12

Table 12-1. Incidentally, task group 1 has undertaken effort to produce a WPAN stand-

ard based upon Bluetooth (v1.1) and in a similar manner to ZigBee the specification

merely covers the PHY and MAC layers.

In our earlier introduction we mentioned that the new revision of the ZigBee

specification (v1.1) will take advantage of the modifications that were made to the

original 802.15.4 specification. You may often see this specification being referred to

as 802.15.4-2003, which represents the year in which the specification was released.

It may be evident that task group 4 is involved in defining the future of this standard.

Within this task group there are further modifications that have been made to the

original 802.15.4 specification. ZigBee v1.1 will take advantage of the 802.15.4b set

of revisions which were specifically commissioned to clarify ambiguities within the

802.15.4-2003 specification. It is expected that the release of the 802.15.4b will coin-

cide with the new release of the ZigBee (v1.1) specification.

The ZigBee Protocol Stack

The ZigBee Alliance has generated several profile specifications that afford the generic

foundation upon which you can create ZigBee-specific applications. In a similar

manner to Bluetooth wireless technology, ZigBee profiles prescribe core use cases or

applications that utilize the ZigBee protocol stack. The core profiles extend to common

functionality, that is, marketed for home, commercial and plant use, but uniquely the

stack provides scalability in that developers can create their own profiles to suit their

particular application. The application will fall into one of the basic profiles as defined

in Table 12.2, which encourage interoperability between ZigBee-enabled devices, very

similar to the Bluetooth strategy. More specifically, a ZigBee network may comprise

several profile types, which collectively form the basis of a distributed application.

Group WPAN Domain

1 Bluetooth

2 Coexistence

3 High data rate

4 Low data rate

5 Mesh networking

Table 12.1 The five task groups within the 802.15 working group that specializes in a

particular wireless personal-area network domain

174 Developing Practical Wireless Applications

For example, a switch on one node will communicate with a light on another node,

in turn, they collectively form a simple light switch (on/off) application. Additionally,

the manufacturer of the switch may differ to that of the manufacturer of the light and,

as such, the profiles assure us of successful interoperation. In creating your own pro-

files, you must inform the ZigBee Alliance who will issue you a profile identifier where

the developer must further define the device descriptions, cluster identifiers and service

types. The profiles for home, commercial and plant have already been defined along

with their respective device descriptions, cluster identifiers and service types.

Understanding the application context

A device descriptor is used to describe the types of devices that a ZigBee-enabled

device is capable of supporting in addition to defining specific data attributes, which

may relate to input/output streams and how such data should be formatted. These

specific attributes can be grouped into clusters which too have their own unique iden-

tifies. It is the characterization of these device descriptors and clusters which uniquely

creates the behavior of a profile. The ability to communicate data between nodes is

achieved using service types; the Key Value Pair (KVP) service is used to provide a basic

command/control mechanism between nodes. The Message (MSG) service type is a

little more dynamic in that it uses the underlying KVP service as the transport mech-

anism to transfer data between nodes, but the payload can be application-specific and

left to the discretion of the developer.

The ZigBee protocol stack, as illustrated in Figure 12.4 comprises several layers,

which conform to the OSI model as we illustrated earlier in Figure 12.3. The stack is

an eclectic number of layers, which are provided by a number of suppliers. For exam-

ple, the PHY and MAC layers are defined by IEEE 802.15.4, whereas the NWK layer,

Application Support Sub-layer (APS), the ZigBee Device Object (ZDO) and Application

Identifier Profile

0 × 00 Network related

0 × 01 Home control

0 × 02 Commercial

0 × 03 Plant control

Table 12.2 A number of stack profile identifiers that may be used within a payload to

specifically identify the profile in operation