ZigBee: Cute Name, Serious Standard

by Morgan Staggers on November 3, 2016 in Wireless

The familiarized name for the IEEE 802.15.4 standard, ZigBee is an open global specification applying to high-level communication protocols for wireless personal area networks (WPANs), home area networks (HANs) and machine-to-machine (M2M) networks using small, low-power radios. Overseen by the ZigBee Alliance and first introduced by Philips Semiconductors, the protocol first saw light of day in 1998. Standardization followed in 2004 with subsequent revisions in 2006 and 2007. Aside — for the non-apiologists among us, a “zigbee” is a portmanteau describing a bee’s “waggle dance,” used to communicate to hivemates the direction where they must fly to find a food source.

zigbee-allianceSource: Zigbee

ZigBee ABCs and XYZs

 ZigBee can transmit from one network device to another over a line-of-sight distance of approximately 70 meters (230 feet); greater distances can be realized by “daisy-chaining” or mesh networking one node to the next. The protocol even features low latency despite the fact ZigBee consumes less power (which limits transmission distance) than Bluetooth and optimized for long battery life measured in months and years. ZigBee operates on non-licensed radio bands of 2.4 GHz worldwide, 915 MHz in the U.S. and Australia, 868 MHz in Europe and 784 MHz in China.

ZigBee utilizes packets with a maximum size of 128 bytes (maximum payload is 104 bytes) transported bidirectionally. This is a low data rate, true, but the applications best suited for the ZigBee standard typically do not require high data rates. IEEE 802.15.4 supports both 64 bit IEEE addresses and 16 bit short addresses. Every device in the ZigBee network is uniquely identified with a 64 bit address, just as they have a unique IP address, and once provisioned the short addresses can then enable the network to support up to 65,000+ nodes or slaves. These nodes can be managed by a single remote control. Superframe time synchronization is an option which can incorporate a guaranteed time slot mechanism for high priority messages.

Common applications include data networking and home/building/industrial automation, e.g., starting the home Blu-ray disc player or TIVO, extinguishing/dimming office lights, engaging a warehouse’s security system, utility metering, etc., all at the touch of a button. Users merely use the Internet for dial-in access. Designed for use in low data rate applications (defined at a range of 20 Kbps to 250 Kbps) where long battery life is needed, ZigBee is best suited for intermittent data transmissions from an input device or sensor. Among the protocol’s very attractive attributes is its capability to operate efficiently in areas with a high degree of radio frequency congestion and interference.

ZigBee standards and releases include the following:

  • ZigBee 2004 — the original standard, defined as ZigBee 1.0 and publicly released in June 2005.
  • ZigBee 2006 — this subsequent version, released in September 2006, introduced the concept of a cluster library.
  • ZigBee 2007 — Publicly released in October 2008, it contains two different profile classes.
  • ZigBee PRO — One of the profile classes of ZigBee 2007, it provides additional features for robust deployments including enhanced security.
  • RF4CE — denoting ‘Radio Frequency for Consumer Electronics,’ this standard applies to audio visual uses. Adopted by the ZigBee Alliance, Version 1.0 was released in 2009.

Here’s a basic video overview of ZigBee from Russian technical consultant Anton “Chip and Dip” Pankratov:

Comparing ZigBee with Other WPAN Protocols

No doubt the reader is aware that there are a number of WPAN and M2M protocols currently in use. Each has distinct advantages and disadvantages; all are in widespread use.

Wireless Infrared

The Infrared Data Association (IrDA) is the international body responsible for governing standards for interoperable, low-cost data infrared (IR) wireless connections. Providing bidirectional line-of-sight high speed connections at short range for point-to-point wireless data transfers, IR wireless “point and shoot” devices are in widespread use across the world. Most people have at least one in their home and/or office. These include peripherals such as TV remotes, wireless computer “mouses” (your intrepid author revels in this usage; “mice” or “mouse devices” is also acceptable), printers, modems and headsets.

As popular as IR is, these devices suffer from limitations. Line-of-sight requirements, as mentioned, is one and the devices must generally be no more than two meters apart. Too, IR waves cannot pass through walls like Wi-Fi can. On the other hand, IR is much more secure, comparable to that of hard-wired systems, and has a very low bit error rate (BER). IR ports cost very little to incorporate into a device. Reportedly, Data transmission rates max out at 4 Mbps, much higher than that available with ZigBee.

ZigBee ‘Remote Control’ (i.e., RF4CE) is designed to replace venerable IrDA standards. Its advantages include bidirectional high speed communication ability, faster response times, increased energy efficiency and no line-of-sight restrictions. RF4CE can be found on many consumer electronic devices including HD and UHD TVs, home theater gear and audio equipment. Manufacturers incorporating RF4CE are Samsung, Philips, Sony, Panasonic and many others.

The latest version of ZigBee Remote Control (RF4CE 2.0), released in 2014, is backward-compatible with the previous version.

Bluetooth

Without a doubt Bluetooth Low Energy (BLE) is ZigBee’s most serious rival for WPAN dominance. Like ZigBee, BLE does not require line-of-sight between devices and can transmit through walls and around barriers. Notably, BLE can transmit data over greater distances than ZigBee, up to 100 meters (328 feet) with amplification. ZigBee is limited to a range of 70 meters (230 feet). While both operate on the same frequency band, Bluetooth splits and exchanges data packets across a 1 MHz bandwidth channel — 79 are available — using a modulation technique known as Frequency Hopping Spread Spectrum (FHSS). ZigBee does not split packets, using Direct Sequence Spread Spectrum (DSSS) instead

According to Link Labs, “these Personal Area Network (PAN) wireless standards have more differences than similarities.”A summary of other differences is presented below:

ATTRIBUTEBluetoothZigbee
Protocol Stack Size250K bytes28K bytes
BatteryMeant for frequent rechargingNot rechargeable
Maximum Network Speed1 Mbps250 Kbps
Network Rangeup to 100 meters (328 feet)70 meters (230 feet)
Typical Network Join Time3 seconds30 milliseconds

Z-Wave

Another WPAN standard in use but not nearly as widely heralded, this proprietary (not open source) technology has key similarities and differences from ZigBee. Both are mesh networks, both use the IEEE 802.15.4 protocol and both have similar applications in security systems, home automation, environmental controls, etc.

Where they differ is

  1. ZigBee utilizes the 2.4 GHz frequency band, meaning it can be used worldwide. This band is notorious for interference and congestion as it is shared with Wi-Fi and Bluetooth. Z-Wave connects on sub-GHz bands — 915 MHz in the U.S. and 868 MHz in Europe.
  2. As mentioned earlier, ZigBee uses DSSS. Z-Wave uses Frequency Shift Keyed (FSK) modulation. For more info on FSK, see here.
  3. Z-Wave range is reported to be limited to 30 meters (98.5 feet); ZigBee tops out at 70 meters.

Coda

 While the ZigBee Alliance claims “reliable” and “seamless” interoperability, competitors and industry observers beg to differ. For example, electronic engineer and blogger Dr. Walter Colitti writes that “the lack of interoperability in ZigBee is due to two main reasons: the lack of an open protocol stack and the lack of a proper certification program.” Link Labs, proprietor of a competing product called Symphony Link, notes that “two ZigBee profiles can interfere with one another.” A separate blog entry adds, “ZigBee’s prime drawback is its inability to communicate easily with other IP protocols.”

But the lack of a dominant standard for WPANs, HANs, etc., is not the foremost concern at the moment facing equipment manufacturers. As key elements of the Internet of Things (IoT), smart appliances must first be secured against hackers and botnets. Otherwise, the world will see repeats of the widely reported distributed denial of service (DDoS) attacks against dynamic DNS provider Dyn on 21 October 2016.

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