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In many ways, the ZigBee standard and the path it has taken to get to this point in time is a lesson in “how to do a standard right.” Many of the members of the ZigBee Alliance — the association responsible for developing the ZigBee standard — had been involved in other standard activities and witnessed firsthand their difficulties. They worked hard to avoid repeating the same mistakes. In the late 1990s, for example, Bluetooth became so overhyped that it could not possibly meet the industry's expectations. To avoid this mistake, the ZigBee Alliance made a firm commitment to “underpromise and overdeliver.” It was not going to talk until it really had something to talk about. That strategy paid off for the organization when it officially ratified the ZigBee standard on Dec. 14, 2004. A little more than a year later, the ZigBee Alliance and its member companies are now ready to talk, having reached a pivotal point in their roadmap — certification. What is the ZigBee certification program and how will it play out in the coming year to drive the emergence of ZigBee-based consumer products? Let's take a closer look.

Before delving into a discussion on certification, it's important to first have a good understanding of ZigBee technology. ZigBee is a global specification for cost-effective, low-power wirelessly networked, monitoring and control products. It defines a set of high-level communication protocols that use small, low-power digital radios based on the IEEE 802.15.4 wireless personal area network (WPAN) standard. Compared to other existing standards, ZigBee is the only technology that can effectively address the unique needs of wireless sensor networks for remote monitoring, home control and building automation network applications in the industrial and consumer markets (Table 1).

ZigBee-compliant products operate in the 2.4 GHz (16 channels), 915 MHz (10 channels) and 868 MHz (one channel) unlicensed bands worldwide and can achieve raw data throughput rates of 250 Kbs, 40 Kbs and 20 Kbs, respectively. Transmission distances range from 10 meters to 100 meters, depending on power output and environmental characteristics. ZigBee's addressing scheme is capable of supporting more than 64,000 nodes per ‘network coordinator.’ Multiple network coordinators can be linked together to support extremely large networks.

The ZigBee protocol automatically constructs a low-speed ad-hoc network of nodes. In most large cases, the network is a cluster of static or dynamic stars. It can also form a mesh or single cluster.

One of the main features of ZigBee is its low power consumption that allows for battery operation of end-node devices. In particular, it supports networks where the end devices are asleep 99.9% of the time, consuming very little power. A very low duty cycle — meaning very few packet data units are transmitted — of the battery nodes within a ZigBee network results in very low average power consumption. It also reduces the likelihood of an unsuccessful transmission. Once associated with a network, the ZigBee node can awaken on an event-driven basis (for alerting) or on a regular reporting interval (for monitoring) to communicate with other ZigBee devices. It then returns to sleep.

When using standard alkaline batteries in a network supporting a typical application, users can expect multiyear battery life. For very low duty cycle applications of < 1%, battery life may exceed 10 years and be constrained by the shelf life of the battery.

There are three different types of ZigBee devices: ZigBee coordinator, full-function device (FFD) and reduced-function device (RFD). The ZigBee coordinator forms the root of the network tree, stores information about the network and can be used to bridge to other networks. Each network has one ZigBee coordinator. Any FFD can act as a ZigBee coordinator. The FFD acts as an intermediate router, passing data from other devices, while the RFD talks to the network but cannot relay data from other devices. The RFD requires the least amount of memory.

Version 1.0 of the ZigBee specification, which includes profiles for wireless home control, was made publicly available on June 13, 2005. The ZigBee Alliance is currently working on version 1.1 of the specification. It will include additional application domains and profiles, which provide the makeup and operation of compatible sets of ZigBee devices in specific market areas. Application profiles are defined and standardized by the ZigBee Alliance Application Framework Working Group (AFG).

The ZigBee certification program was developed as a means of ensuring interoperability, where appropriate, between end products. Certification is important on a number of levels. Standards, after all, can create a market but only if they are implemented in a consistent way. Certification offers a practical means of verifying correct and consistent implementation of the ZigBee specification. In the process, it creates end-user confidence around interoperability.

According to Bob Heile, chairman of the ZigBee Alliance, “If we ensure products fit easily and completely with each other, then the potential for developing new and exciting applications will be limitless. In home environments, for example, applications that control home security can easily be linked to lighting applications where a sensor detecting an open door or window would alert lights to immediately turn on.”

The ZigBee certification program is an independently administered testing process for products before they enter the market. It ensures that they are fully interoperable “out of the box” and can easily form into a single, cohesive ZigBee network capable of passing data for all applications on the network. Testing, which includes standard test cases and reporting metrics, is performed by one of two independent test service providers: National Technical Services Inc. or the TUV Rheinland Group.

Manufacturers, original equipment manufacturers (OEMs) and developers can qualify for certification via one of three test programs, which include:

1. “ZigBee compliant platform” (ZCP) — tests modules or platforms that are intended to be used as building blocks for end products.

2. “ZigBee certified” — tests apply to end products built on a ZCP using a ZigBee public application profile. After successful completion of the program, the product may bear the ZigBee Alliance logo, per the ZigBee trademarks, designations and logos policy.

3. “ZigBee network capable” (ZNC) — tests products built on a ZCP but using a non-public ZigBee application profile. Testing ensures that such products coexist successfully with products and networks certified by the alliance.

Each program uses unique test plans. The ZCP program, for example, encompasses all but the application interoperability layer of the ZigBee stack profile. The certified product program focuses on the application and interoperability layers of the ZigBee stack profile. The ZNC program encompasses only basic ZigBee Alliance functionalities inherent in all ZigBee devices.

The ZigBee Alliance grants ZigBee certification based on one of the three test programs when the following requirements are met (Figure 1):

1. A company applies for ZigBee Alliance certification.

2. The member company submits the product(s) to one of the two ZigBee-designated test providers.

3. The ZigBee Alliance certification body receives notification from the test provider, along with the vendor, that the product has successfully completed certification testing. This notification process does not include test results or confidential vendor information, only a general ‘pass’ statement.

4. The company provides the appropriate paperwork to the certification body.

5. The ZigBee management firm confirms the membership status of the company as a “member in good standing” with all dues and fees paid.

6. The ZigBee Alliance receives the lab test results. Within five business days it conducts a review, approves the cost and provides logo usage rights to the submitter company.

7. A ZCP is used for the final product.

Once a product has been officially certified it is added to a public registry maintained by the ZigBee Alliance. This registry, along with a detailed list of devices and version numbers can be accessed on the web at www.zigbee.org/en/products/. The types of products that can be certified are products that implement a public application profile (one that has been ratified through the AFG), such as home control lighting. Those companies eligible to apply for ZigBee Alliance compliance testing include ZigBee Alliance member companies and adopter companies in good standing.

An additional way for manufacturers to ensure interoperability of their products is by participating in regularly scheduled ZigFests. These events allow manufacturers to come together to showcase their products and network with other wireless technology professionals. Several test cases and runs are facilitated with different pairings of manufacturers. All participant identities are kept confidential and known only to the other parties at the event.

To date, a total of 14 devices have received ZigBee certification. This includes: six ZigBee-compliant platforms from Airbee Wireless, Ember Corporation, NEC Engineering, Silicon Laboratories and Texas Instruments (formerly known as Chipcon); a development kit from CompXs (acquired by Integration Associates); ZigBee-compliant modules and development tools from Helicomm; a ZigBee stack from the Institute for Information Industry; and transceivers from Freescale Semiconductor.

The ZigBee platform is a hardware/software design that enables OEMs to develop a wide range of ZigBee-based products (Figure 2). ZigBee-compliant platforms include the IEEE 802.15.4 radio and the ZigBee stack up to the application layer and are available as either chips or modules for use in end products.

In addition to these ZigBee-certified products, there are a slew of device and chip/firmware vendors. Some of today's device vendors, for example, include:

• Cirronet (www.cirronet.com) — offers a range of ZigBee wireless mesh networking products such as OEM modules (e.g., the ZMN-2400 2.4 GHz module), gateways, signal-conditioning boards and sensor modems.

• Crossbow Technology (www.xbow.com) — offers the MICA2, MICA2DOT, MICAz and MCS Cricket radios; OEM modules compatible with a wide variety of Crossbow sensor modules. MICAz is the 2.4 GHz ZigBee radio.

• EnOcean (www.enocean.com) — offers ZigBee bridges that provide a seamless link to ZigBee networks.

• Helicomm (www.helicomm.com) — offers a complete ZigBee/802.15.4 hardware, software and tool platform, which includes the 8051-based IP-Link modules.

• Innovative Wireless Technologies (www.iwtwireless.com) — offers the wireless AXON modules capable of running ZigBee-compliant software (Figure 3).

• Luxoft Labs (www.luxoftlabs.com) — offers a ZigBee development kit and the MeshNetics ZigBee modules.

• MaxStream (www.maxstream.net) — offers the XBee and XBee-PRO 2.4 GHz radio modems and with a serial UART interface and the XBee development kit.

• Microchip (www.microchip.com) — offers a ZigBee demonstration and development platform that supports multiple RF transceivers.

Some of today's chip/firmware vendor's include:

• Atmel (www.atmel.com) — offers the AT86RF210 Z-Link ZigBee-compliant radio chip operating at a frequency range of 868 MHz and 90 MHz to 928 MHz.

• Ember Corporation (www.ember.com) — offers ZigBee-compliant 2.4 GHz radio chips (e.g., EM250, EM260 and EM2420), as well as the EmberZNet ZigBee protocol stack firmware.

• Freescale (www.freescale.com) — offers low-power RF transceivers, such as the 2.4 GHz MC13193 data modem, as well as the full ZigBee stack for its devices.

• Helicomm — offers ZigBee/802.15.4 stacks, profiles, and tools for Freescale/8051 MCUs and leading 802.15.4 transceiver ICs.

• Integration Associates (www.integration.com) — offers the EZRadio PHY, MAC layer, ZigBee-compliant CompXs software stack, development kits, reference designs, modules, and support services.

• Jennic — offers the JN5121MOxxx modules, JT24Z001 2.4 GHz transceiver and JS24Z121 2.4 GHz SoC (Figure 4).

• Oki Semiconductor (www.okisemi.com) — offers the ML7065 2.4 GHz ZigBee/802.15.4 low-power integrated single-chip transceiver built on a ZigBee-certified development platform.

• San Juan Software (www.sanjuansw.com) — -develops firmware and ZigBee application-level software.

• Silicon Laboratories (www.silabs.com) — offers component level to complete drop-in wireless solutions, including microcontrollers and development kits.

• Texas Instruments (www.ti.com) — offers the 2.4 GHz CC2420 ZigBee development platform (including hardware), the ZigBee protocol stack, as well as development tools and the CC2430 ZigBee system-on-chip (SoC).

While these companies represent just a sampling of the vendors now involved in this burgeoning market, they serve to illustrate the growing momentum behind the ZigBee standard. This momentum will remain strong, and all the more invigorated by assurance of product interoperability at the consumer level. Here, certification testing will play a critical and essential role in the standards' widespread, global adoption.