06/05/2005

Zigbee

Zigbee is a new standard that's going to make a huge difference in the world of industrial communications and even in home automation.

Zigbee comes out of the Institute of Electrical and Electronic Engineers (IEEE) in the US, the same people who specify WiFi and even Bluetooth (it comes out of the 802.15 group which is the same as Bluetooth).

Though Zigbee only offers low data rates (up to 250Kb/s, compared to 1Mb/s for say Bluetooth or 11Mb/s for 802.11b) it is extremely flexible, supports a variety of network configurations and is self configuring. There can be 65,000 devices in one Zigbee network.

Zigbee devices are meant to be low power, they turn themselves off when not in use, it's the life of the battery which is likely to determine the life of the device. Of course having devices turn-off randomly means the network has to reconfigure itself quite regurlarly but that's where it's very efficient and it takes about 30mS (Bluetooth takes up to 3 seconds).

There's 3 types of node in a Zigbee network, ZC (controller), ZR (router) and end-node. There's only ever one ZC which controls the complete network in a heirarchical tree, lots of ZR's and each ZR is connected to end-nodes. The ZR's are allocated address space by the ZC, and then further sub-allocate their address space to the end-nodes. Networks can take vairous configurations including complicated mesh designs.

Since the networks are self-healing and very quick to recognise new nodes etc, it would seem to be a perfect solution to WiFi mesh networks, just implement the Zigbee stack on top of the WiFi radio hardware, and citywide networks supporting 65,000 nodes suddenly become easy to do - now someone just needs to do it.
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