Names and temporary addresses

The name that stays

Every Zigbee device has a 64-bit hardware address, the EUI-64. It was made for the device and it does not change. It identifies the device. It is not proof of who built it or that it is genuine, because a number can be copied.

The label that changes

On joining, the coordinator assigns a 16-bit network address, the short address. It means something only inside this network, and it can be different after a rejoin. The coordinator's own is 0x0000.

The bench rejoins one device. The long address is the same afterwards and the short address is different. The device did not change, and neither did its place.

The names of the network

A network has names too: a 16-bit PAN ID and a 64-bit extended PAN ID. Both identify the network, at different levels, so radios can tell it from a neighbour's. They are not names for people or rooms, and the values on the bench are examples.

Sixteen bits allow a very large number of short addresses. That is a limit of the address space, not a size to run. How large a network can get depends on its traffic, topology, device memory and coordinator, and is something to test.

What it costs when it goes wrong

Anything that remembers a device by its short address can lose it after a rejoin: a script, a stored rule. The device is still there and the label no longer points at it. Remember the long address and the problem does not arise. An address is not a place, which is why this bench has no house. The next lesson covers how a device gets its address.

Common mistakes

• Keying a device on its short address. It can change at a rejoin. Use the EUI-64.
• Treating the EUI-64 as proof of identity. It identifies a device and does not authenticate it.
• Reading 16 bits as a size to run. It is a ceiling on the address space. A real network is limited long before.