Maximum amount of nodes in Thread star topology

RE: Maximum amount of nodes in Thread star topology

Jørgen Holmefjord — Tue, 26 Mar 2019 10:01:52 GMT

It would not help to run this on the Raspberry Pi/BeagleBone platforms, as the full OpenThread stack still runs on the NCP and you are limited by the capabilities of the NCP device. For this to be possible, you would need the architecture described in Host/802.15.4 Controller platform documentation. This platform is currently not supported in our SDK.

I did some quick tests with network attachment, by toggling a GPIO in start of main function, and when receiving the CHANGED_ROLE flag. By resetting the board at different intervals, I see varying time ranging from 40 ms to 3 seconds. It seems to take longer if the child have timed out from the network.

RE: Maximum amount of nodes in Thread star topology

Aleksandr — Mon, 25 Mar 2019 11:52:55 GMT

Hi Jorgen,

Thank you for the reply. I got your point

In case we would use Raspberry Pi (or BeagleBone) as Border Router&Network Leader&Router can we solve this problem? The host then has a lot of DDR RAM.

In case we will follow your the first advice in the first post (to have only active device in the network) how much time will take to get connected the network from the wake-up till get the first message? May be you have some estimations?

Aleksandr

RE: Maximum amount of nodes in Thread star topology

Jørgen Holmefjord — Mon, 25 Mar 2019 10:35:53 GMT

Frequent flash writes/erases will heavily affect the performance of the device, as the CPU/radio is blocked during these operations. The number of flash write/erase cycles are also limited, and this will cause rapid weardown of flash. Modifying this will require large changes to the OpenThread stack, and is not something I can recommend that you do.

Routers need to buffer messages for end devices. The default in our prebuilt OpenThread stack is 32 children and 160 buffers (each 128 bytes large). You can try modifying these numbers, but I'm not sure a single node can service that many nodes.

RE: Maximum amount of nodes in Thread star topology

Aleksandr — Fri, 22 Mar 2019 15:44:12 GMT

Hi Jorgen,

Thank you for the reply!

We would like it to be a part of a network all time. The reason behind this is that we need a very short time from wake-up till starting of messages receiving from the router. I expect that when a node sleeps and is excluded from the network it would take larger time to re-establish connection again (like discovery/advertisement delay in BLE). We need a reaction time of 0.5s since a device wakes-up.

The network will be consisting of one router and 200-300 nodes. We don't want to have a mesh network because all devices will be battery powered.

But shouldn't it be possible to store the information about the network in the FLASH? I believe it will require additional SW effort?

Aleksandr

RE: Maximum amount of nodes in Thread star topology

Jørgen Holmefjord — Fri, 22 Mar 2019 13:59:38 GMT

Hi,

The theoretical maximum number of childrens for a single router in Thread is 511 nodes. The maximum number of supported devices will be limited by the RAM, as routers need to store information about nodes, and also buffer messages for sleepy end devices. The minimum required by the spec is 10 nodes.

When you say that the devices will be in deep sleep mode, I assume that they will not be a part of the network in this state? In that case, I think it should be possible for a router to maintain 20-30 nodes, but I have not tested this myself. If you want all 300-400 nodes to be part of the network at all time (sleepy end devices), I do not think this will be possible.

What will be the total network size, i.e., are you planning to have multiple routers with this amount of children?

Best regards,
Jørgen