BLE Multi-Link connection - Maximum devices

RE: BLE Multi-Link connection - Maximum devices

Amanda Hsieh — Fri, 10 Jul 2020 09:25:34 GMT

With Nordic softdevice s140/s132 as the example in the demo video, you only can control 19 devices simultaneously, but you can take a look at this post.

The support staff is reduced during the summer holidays, and you may experience delayed answers.

-Amanda H.

RE: BLE Multi-Link connection - Maximum devices

believer — Fri, 10 Jul 2020 02:19:55 GMT

Thank you for the very detailed information.

In my application, I want my app can control about 20 devices simultaneously. Can I do that with BLE?

RE: BLE Multi-Link connection - Maximum devices

Amanda Hsieh — Thu, 09 Jul 2020 07:58:50 GMT

Hi,

In that video, the phone only connected to the aggregator running on an nRF52840DK which will collect information on all the connected devices and relay the information to the UART and to the connected smartphone over BLE. From the phone application, the user can control the LED color and state of the connected devices. The video illustrates the multi-role and multi PHY capabilities of the Nordic SoftDevices running on nRF52840DK. By using the 20 link feature of the S132 or S140 SoftDevices the aggregator can connect to up to 20 devices at the same time, where 19 of these devices will be ble_app_blinky or Thingy devices, and 1 device can be a smartphone. As for Android BL concurrent connection maximum, please see this thread.

-Amanda H.

RE: BLE Multi-Link connection - Maximum devices

believer — Tue, 07 Jul 2020 02:59:50 GMT

Hi, I have seen this video. As you can see, an Android device phone can control 20 devices at the same time.

I have some unclear ideas with your answer, can you explain about 7 & 20 connections as mentioned above?

RE: BLE Multi-Link connection - Maximum devices

Amanda Hsieh — Mon, 06 Jul 2020 13:06:31 GMT

Hi Mike,

[quote user="Mishka"]With "non-simultaneous links" I mean that it's possible to know about more than 20 devices (i.e. keep bonding information), but not get into formal connection with them. On central, the application scanner may catch some more devices and the app could decide to drop few existing connections in favor of the new discovered. Will that work?[/quote]

The limit of 20 is 20 concurrent links at the same time, that is 20 devices that are in a connection right now. We do not have a number for how many bonds the application can store (this is outside the scope of the SoftDevice, who only controls the current connections.)

So yes, the application can do as you suggest.

-Amanda H.

RE: BLE Multi-Link connection - Maximum devices

Mishka — Mon, 06 Jul 2020 12:33:20 GMT

Hi Amanda,

thanks for the clarification. With "non-simultaneous links" I mean that it's possible to know about more than 20 devices (i.e. keep bonding information), but not get into formal connection with them. On central, the application scanner may catch some more devices and the app could decide to drop few existing connections in favor of the new discovered. Will that work?

I admit it's unfair to call this kind of operation a link. Sorry for the confusion.

RE: BLE Multi-Link connection - Maximum devices

Amanda Hsieh — Mon, 06 Jul 2020 11:55:05 GMT

[quote user="Mishka"]However, it should be possible to maintain more than 20 non-simultaneous links, i.e. maintain number of connection handles below the limit.[/quote]

I don't think so. The limitation is in the SoftDevice's scheduler and memory. The maximum number of linked devices depends on how much memory you've got and how much memory is required for each link depending on the content of the linking information.

-Amanda H.

RE: BLE Multi-Link connection - Maximum devices

Mishka — Mon, 06 Jul 2020 11:32:57 GMT

Hi,

I doubt so, because an Android device will limit the number of concurrent connection to only 7 as defined with BTA_GATTC_CONN_MAX (please see Android Bluetooth stack).

Also, the SoftDevice limits total number of concurrent connections to 20 (i.e. as central + peripheral). However, it should be possible to maintain more than 20 non-simultaneous links, i.e. maintain number of connection handles below the limit.