The maximal number of devices for one coordinator

I think that you might be slightly confused.

If you are using a ZigBee 2007 network, it's true that you can only have 32 non-routing end devices (ZED) for a ZigBee network.  These devices could all be sleepy and would receive their information and talk only to the coordinator.  This network type would be 'Star'.

However, most ZigBee networks are not made up of only sleepy end devices and contain fully functioning routers.  For each of these fully functioning routers in addition to the coordinator, an additional 32 sleepy end devices (ZEDs) can be supported in the system.  So the number of non-routing devices in a network is (1+n)*32 where n is the number of fully functional devices (not including the coordinator) that are present in the system.

That being said, the number of routers permissible in a system is theoretically infinite.

Hope that helps...

Thank you so much for  your reply. I get your idea.

The devices  in ZigBee system can have a  Tree structure that the Full functioning devices FFD can be the parents of the reduced functioning devices RFD.

And I think the number of routers might not be infinite because the limitation of address allocation which is 2^16.  Is that correct?

However, what I am concerned here is, for one router, Can more than 32 devices (FFD or RFD) directly link to it?

Someone said the maximal number is 32 since they use 32 bit bitmask here, I am not very clear about the principle here. Could you kindly help me on this?

Best, Thanks a lot!

You're getting there for sure!

You're right on the number of routers as well.  Routers actually have a unique 64-bit long address that is determined when the chip leaves the factory.  However, network addressing can only support so many short addresses... so 2^16 is true.  For most intents and purposes this number is infinite because you will likely run into routing and latency problems if you're supporting that many devices on a single network.

For one router, no more than 32 devices can directly link to it.  This is based on, as people have said, the bitmask.  Basically, as far as my understanding goes (someone correct me) this just means that the list where the device's associated network addresses are stored has only 32 entries.

There's a thread here: http://e2e.ti.com/support/low_power_rf/f/158/t/17257.aspx that goes over some of this.  Something to be aware of is that this is only for the addressing of the network (tree addressing) and will not define the routing.

Hope this helps...