Questions about Thread network

[Fabien Comte]

Hello,

I have questions about Thread protocol:

- Can i ask to network the ID of the last point used to connect a sleeping device ?

- I have a great area to cover so can i bypass Thread number of nodes / devices limitation with a hack (not compatible with thread anymore) ?

- Can i have side by side 2 or more thread networks with the same ID / password (my sleeping devices are moving in the area) ?

- Is Thread robust about security and jamming ?

Thank you.

[Edvin]

Hello,

- Can i ask to network the ID of the last point used to connect a sleeping device ?

I don't understand this question. Do you want a device to keep the network ID the next time it connects?

- I have a great area to cover so can i bypass Thread number of nodes / devices limitation with a hack (not compatible with thread anymore) ?

If you bypass the number of nodes with a hack, it would not be Thread compatible anymore. The address field in a thread message is the limiting factor, so if you increase the size of this field, it would no longer be recognized as a thread message.

- Can i have side by side 2 or more thread networks with the same ID / password (my sleeping devices are moving in the area) ?

You can have two networks in two different places, but if some of the nodes in the network can hear both the networks, it will not work. The Thread network is self sustained. Let us say you have a network with "two parts", where only one node can hear both parts. So that node will be the "bottle neck". If that node disappears (is powered off), then the network will split in two. The part with the leader node will keep that node as the leader, and the other part will dynamically select a new leader. If the node that disappeared is powered on again, the two networks will connect, and since they now have two leaders, one of them will go back to being a router node, so that the network only has one leader.

So if you have two networks with same ID / password, then the networks will merge, and if it is too large, then I guess some of the nodes will be kicked out.

 

Regarding the number of nodes, you can have 32 router nodes in Thread, and each router can have up to 511 child nodes / end devices, so theoretically, you can have more than 16 000 nodes in a thread network.

- Is Thread robust about security and jamming ?

yes. Thread networks are encrypted. Jamming? Depends. If you have a device making too much noise on the channel used, so that none of the nodes can hear anything, then it will fail. This scenario is usually not a problem.

 

Most of your questions can be answered from this site. You should read through it if you want to better understand the network setup.

[Fabien Comte]

Thank you,

First item: I wan't to know where is a device in the network (I know locations of routers)

Bonus questions please:

- is network search / join radio traffic detailed somewhere (like advertising / connection sequence for BLE)

- if end devices move, do they jump to the best router ?

- how much is current consumption for a nRF82840 to still connected as end device ?

- can an end device scan for several networks (like Wifi, no multiple scan but one scan with a coded selection) ?

- how long and how much current is scan to connect sequence ? 

[Edvin]

Hello,

Since thread is a routed mesh network, it is not really well suited for moving nodes. An end node will only communicate with it's parent node, until it decides that the connection is lost. Then it will start to advertise to get a new parent node.

You can see what parent node you have, and what the routes are to a certain other node, so I guess you can use this to estimate the position.

Bonus:

- Yes. The link that I sent you in the previous reply has some tabs on the left hand side. Check out the tab about Network Discovery and Formation.

- After some time, yes, but not immediately. I am not 100% sure whether they move after some time when they see that there is a better option, or if this first happens when the device disconnects from it's current parent node.

- This depends on the setup. I suggest you read through the MTD example description here.

- The procedure in joining a Thread Network is that you first do the Thread Commisioning. In the commissioning process the network credentials are being obtained, and hence, it knows what to scan for. If you have commissioned for two different networks, I guess you can switch between scanning for them.

- Depends on how soon it is discovered. 

https://openthread.io/guides/thread-primer/network-discovery

Best regards,

Edvin

[Fabien Comte]

Thank you.