ZigBee and ZigBee PRO: Which feature set is right for you?

by Brian M. Blum, ZigBee Product Marketing Engineer, Texas Instruments , TechOnline India - October 06, 2008

For those new to ZigBee or who have not yet had a chance to digest the latest specification, this article serves to explore the status quo of ZigBee, provides an overview of the ZigBee and ZigBee PRO feature sets, and discusses ZigBee in the context of various markets and applications, including a discussion of ZigBee's applicability to the medical market.

ZigBee has come a long way, especially since many first heard about the new wireless standard poised to revolutionize the home automation market. For those new to ZigBee or who have not yet had a chance to digest the latest specification, this article serves to explore the status quo of ZigBee, provides an overview of the ZigBee and ZigBee PRO feature sets, and discusses ZigBee in the context of various markets and applications, including a discussion of ZigBee's applicability to the medical market.

How ZigBee and ZigBee PRO Feature Sets Differ
ZigBee has recently ratified the ZigBee-2007 specification which defines two feature sets called ZigBee and ZigBee PRO. Building on the ZigBee-2006 specification, the new 2007 specification provides enhanced functionality and is backward compatible under certain network scenarios. The ZigBee feature set provides tree addressing, AODV mesh routing, unicast, broadcast and group communication, security, and much more. ZigBee PRO replaces tree addressing with stochastic addressing. It includes the same AODV routing used in ZigBee (2006 and 2007), but provides many-to-one source routing as an alternative. ZigBee PRO also adds limited broadcast addressing and adds support for "high" level security. Both ZigBee and ZigBee PRO feature sets provide additional support for optional frequency agility and fragmentation.

ZigBee's tree addressing assigns addresses hierarchically, while ZigBee PRO utilizes a stochastic addressing scheme which randomly assigns addresses to devices and sorts out conflicts by continuously monitoring and reacting to "management" traffic. ZigBee benefits from guaranteed unique addressing and is free from the overhead of constantly monitoring communication and dealing with address conflicts. However, PRO benefits from scaling such as when communication limitations result in a network comprised of many (five +) hops, or when a network is comprised of potentially many mobile end devices. This benefit comes with the price of increased startup delay as ZigBee PRO must allow time for address conflict resolution, which is not necessary for tree addressing.

Both ZigBee and ZigBee PRO routing utilize ad-hoc on-demand distance vector (AODV) routing, but only PRO also supports the many-to-one source routing option. At the expense of a larger protocol stack, many-to-one source routing allows fast route establishment where many devices (e.g., sensors) are all reporting to a single sink (e.g., network gateway device). For unsolicited bi-directional and peer-to-peer communication (e.g., light switch and light), the many-to-one feature becomes less effective and in some cases inappropriate.

Both ZigBee and ZigBee PRO support group addressing, but PRO adds support for limited broadcast group addressing that prevents unnecessary flooding of the entire network when all group members are in relative close proximity. This feature can be useful in reducing network wide communication overhead for large networks, but comes at the expense of using additional precious code space.

Although several additional minor differences exist, the last feature difference between ZigBee and ZigBee PRO is support for high security. High security provides a mechanism for establishing link keys between peer-to-peer connections, and adds additional security when devices on a network may not be trusted at the application layer. Like many PRO features high security can be helpful for certain applications. But it comes at a significant expense with respect to utilizing precious code space that could be used by the application.

While ZigBee and ZigBee PRO share a majority of their features, it is important to know that ZigBee and ZigBee PRO devices play together on the same network only under limited circumstances. If the established network (established by the coordinator) is a ZigBee network, then ZigBee PRO devices will only be able to join and participate in that network under the end device role. This means that the device will communicate into that network through a parent (router or coordinator), and will not take part in the routing or allowing additional devices to join the network. Similarly, if the network is initially established as a ZigBee PRO network, then ZigBee devices will also only be capable of participating under the limited end device role.

Many of the products using ZigBee will, in essence, be proprietary or implement a private profile or application specification. This means that any given network will likely only contain devices sold by a specific company or conglomerate of companies. This is especially the case for medical where no public profile currently has been defined and ratified. In this case, ZigBee will be used for features such as its mesh routing protocol, communication redundancy, and low power operation. However, for markets where devices from various vendors must function as a single cooperating network to perform the designated service or function, public profiles have been specified to ensure that all devices on the network speak a common language and can achieve interoperability. Interoperability in this context means that a product from some company A (light switch) will be able to communicate with a product from a second company B (light ballast) without those companies working together a-priori to ensure the devices work together (Figure 1).

Figure 1: Typical ZigBee products for home automation

During the initial years of ZigBee, the technology's main focus remained on the home and commercial building automation market. As more companies and professionals are exposed to ZigBee and better understand its capabilities and nuances, ZigBee has burgeoned and is being designed into quite an extensive range of additional markets. Most prominently ZigBee has made its way into advanced metering infrastructure (AMI), as well as being designed into products that focus on elderly care and assisted living, medical, telecom, asset tracking, entertainment, and more.

{pagebreak}In addition to the ratification of the ZigBee-2007 specification (ZigBee and ZigBee PRO feature sets), the Zigbee Alliance has been focused on finalizing and formally testing several application profiles that define the types of devices supported in a network and the language of communication between these devices. Home automation (HA) was the first ratified public profile that has been mature and available for quite some time. Smart energy (SE) that targets AMI is currently ratified and on its way to complete final testing and Golden Unit certification in May 2008. Commercial building automation (CBA) is poised for testing soon, and as more companies develop products and contribute within the Alliance, more public profiles will follow. Medical, or more specifically personal health and hospital care (PHHC), is one of these areas. It will likely receive increased focus in the near future as it looks to implement the IEEE 11073 standard over ZigBee.

Personal Health and Hospital Care Applications
Still in early stages of development, PHHC devices will not likely be available on store shelves in the next 12-18 months. But, that has not prevented companies from building ZigBee-powered devices in this market. The medical market, including assisted living and home care has discovered that the ZigBee networking protocol can be extremely beneficial and cost effective. ZigBee provides an inexpensive solution for portable medical applications such as monitoring and reacting to emergency scenarios, monitoring patients or elderly persons as they go about their daily routine, and provide real-time data that can speed up the reaction time of care personnel and save lives. Residents of assisted living centers can achieve peace of mind knowing that someone is only moments away, and facility personnel can monitor residents on a much larger scale without intruding on their daily lives (Figure 2).

Figure 2: Examples of portable medical monitoring applications

In an assisted living application, the ZigBee network allows for the reliable and imperceptible collection of data in real-time. This could include anything from tracking the location of a resident in their home, monitoring eating or bathroom habits, ensuring medication is taken regularly and on time, collecting weight, blood pressure, or other bio-metrics, and enabling automatic lighting or doors to prevent accidents. The list goes on and on, and the technology has already proven itself in real deployments.

ZigBee is also being applied to asset tracking in hospitals and medical facilities. Utilizing the extensive multi-hop mesh network, ZigBee allows expensive equipment to be tagged and tracked throughout a large facility. With limited equipment available and the need to share such equipment across multiple units and floors, knowing where expensive equipment resides at any given time can save money and lives. ZigBee provides such a solution in an easy to setup network that can be deployed for a minimal cost. There are many other potential uses for ZigBee in the medical space, many of which are under development as you read this article. To date with the lack of a public profile available, these systems will remain single vendor solutions and will not be interoperable. However, in many if not most cases, this is desirable because the product can be customized to meet the specific system requirements without concern for other vendor products. Both ZigBee and ZigBee PRO can be utilized in this market depending on system requirements and the scale of the deployment. So if you are looking to utilize ZigBee in your product or system, please consider what you have read above and contact a ZigBee vendor for more information.

For more information about Zigbee solutions, visit: www.ti.com/zigbee.

About the Author
Brian M. Blum is a Zigbee Product Marketing Engineer with Texas Instruments where he is responsible for 802.15.4 and ZigBee LPRF product line. He received his Master's of Computer Science w/ focus on Wireless Sensor Networking from (university name/s). In his spare time he enjoys rock climbing, volleyball, yoga and nature. Brian can be reached at ti_brianblum@list.ti.com.

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