This chapter describes how ZigBee applications interact with other ZigBee applications. It describes what constitutes a ZigBee network, how individual nodes are addressed, and how to address application objects within a node. Terms such as PAN ID, extended PAN ID, network address, profile ID, cluster, endpoint, attribute, and command will become clear (if I have done my job).
This chapter is filled with plenty of examples. If you're a developer and read only one chapter in this book, read this one.
But first, as usual, the real truth about how ZigBee gained its name.
ZigBee. Zig ...B ee...
Bees. The origin of ZigBee came from the peculiar behavior of bees, first noted in the 1960s by Nobel Prize-winner Karl von Frisch. Bees, after zigging and zagging around in the fields, return to the hive, and perform what some call the Waggle Dance to communicate the distance, direction and type of food to others in the hive. After receiving a WAGGLE-DANCE.indication, bees fly off directly to the source of food.
"We have solved it once and for all," said Professor Joe Riley, team leader at Rothamsted Research, an agricultural research center. The team tracked a group of bees as they flew to a food source. To track bees by radar, the researchers first had to create a transponder small enough and light enough so that a bee could carry it. The transponder weighed approximately 10 to 12 milligrams, a fraction of the pollen load bees are accustomed to carrying.
Opponents to the Frisch theory have suggested that while the bees dance, it s not to convey information. They believe bees are actually guided to the food source by odor conveyed by the scout bee. Von Frisch, on the other hand, claimed that recruits understood the dance and flew directly to the food source. But "the bees take five to 10 minutes, not one minute," said Riley.
To make sure bees were not following a scent, a control group of bees was transported 250 meters after seeing a Waggle Dance. When released, the bees flew off in the direction indicated by the dance, the team at Rothamsted Research found.
The team's results show that bees do decode the dance and fly off immediately in the direction indicated. But, "they very rarely get it absolutely right," said Riley. "The mean error is about 5 to 6 meters." Once the bees get to the end of the flight, they change their flight pattern, and start zigging and zagging, looking for the food they were instructed to find. That takes time, Riley said, sometimes up to 20 minutes.
ZigBee chips do not currently fit onto the back of a Bee, but they do come in 5 ◊ 5 mm packages, and consume so little power they can last longer than the lifetime of a bee on a couple of AAA batteries.