Hi,
I’ll be using a set of XBee 3 modules as end devices controlled by a central hub (a Raspberry Pi with an XBee module) in a star network configuration.
As I’ve been reading up on the Zigbee specification, I’ve seen that when you need to send a message to multiple devices at once, it can be more efficient to broadcast the message rather than unicast it to each device individually.
However, I’ve also come across several notes and discussions mentioning a commonly cited limit of roughly one broadcast per second, due to the risk of network flooding when each router repeats the broadcast.
My question is: Is it correct to assume that this broadcast frequency limitation only applies to mesh networks (where routers repeat broadcasts with a radius > 0)?
And, in a pure star network, where the coordinator sends a one-hop broadcast to all directly connected devices, is there any reason to limit broadcast frequency (beyond the usual bandwidth and CSMA/CA channel-sharing constraints)?
If this is really a star network where all remotes are in range of the master, then you should not be using a mesh network. Instead, you should be using a Point to point, point to multi-point protocol such as 802.15.4. In an 802.15.4 or Point to multi-point network, you can send broadcast packets considerably faster than you can in a mesh network. That is, you can send broadcast packets several times per second verses once per second in a mesh.
I am having a hard time understanding one thing, you tell me that I should not be using a mesh network, which I dont plan to do, but isn’t one of the great things about Zigbee 3 that it supports many types of topologies, one of them being point to multipoint (star) topologies? Here is a snip from your website: What is Zigbee? Learn About Zigbee Wireless Mesh Technology | Digi International
Both of these explanations point to the possibility of using Zigbee devices in point to multipoint network. Wouldn’t this network set up be done by configuration, say by Choosing NH and broadcast radius of 0?
Yes, you can configure a Zigbee network in a point to multi-point or star topology. However, it is still going to treat it as a mesh. The lower level 802.15.4 protocol is a true peer to peer, point to point, point to multi-point network topology that you are asking for. it is the lower level protocol that a Zigbee network operates on.
To be clear, the Zigbee protocol operates in the Networking layers of the OSI model where by the 802.15.4 protocol operates at the PHY and MAC layers.
So the limit on the frequency of broadcasts will be the same using the Zigbee protocol even though you configure it as a multi-point topology essentially?
