Define "associate" and it use in XBee context


My first post so bear with me. I have been experimenting with some XBee S2’s and will have a few questions as I go. so this it the first How is the term “associate” used?

Traditional radio systems worked by an independent nature and CDMA, so “I talk when I think I can, and I talk regardless if any peers can hear me.” In fact, some just talked and ignored if the channel was busy, retrying as required.

The 802.15.4 (lower level of ZigBee) introduced the notion of a PAN/network and associaton, which just means every node must join a PAN or network. No lone-wolves or random ‘howling’ allowed.

A Coordinator just blindingly makes its own PAN/network. It doesn’t matter if a dozen existing PAN/networks share the same frequency. Even PAN-id collisions can occur.

A Router/End-Device need to find a PAN/network to join. They scan/move between frequencies (channels) until they find one talking the supported protocols & allowing joining or association. If they have a fixed PAN id (recommended), then they also demand the expected PAN ID.

One oddity you’ll find - once a router has belonged to a PAN, it will pretend to be associated as long as it can find atleast another router claiming to be in that PAN (if JV setting = default of 0). Why tolerant the coordinator going away & coming back at will.

This confuses beginners, because they will change the PAN ID of the gateway, reboot it and wonder why NO ONE re-joins, and yet all the old routers sit out there happily blnking the associare LED as-if joined (a very annoying habit!)

Setting JV=1 (which I always do) causes the routers to eventually reliaze they ‘lost’ the coordinator, so they go off and try to find it again. It causes all the routers (and thus all the end-devices) to change as the gateway/coordinator does. This also means if the gateway is powered off say every night, then all the routers will spend the night looking for a new home and be unable to communicate to anyone. That is why JV=0 is the default, as it allows a group of peers to stay togather and talk even if the coordinator goes away temporarily.

A good description, thanks for the education.