BT_HCI_ERR_INSUFFICIENT_SECURITY during re-discovery

[muli]

Note. This issue only occurs if using the Nordic Soft Device controller or the Packetcraft controller. 

I am working with the nRF5340 audio development boards. 

I have a project with a central device (used as a Broadcast Assistant) and a peripheral device (used as an audio broadcast receiver). They both form an ACL connection and exchange data. 

Whenever the receiver is syncing to a broadcast source and it gets disconnected from the central for whatever reason, the central manages to re-connect to the peripheral, however the BASS discovery fails with BT_HCI_ERR_INSUFFICIENT_SECURITY. The following error is displayed : 

<wrn> bt_gatt: gatt_exchange_mtu_func: conn 0x200018c8 err 0x0e

 . 

The only way to solve this is by rebooting the receiver / peripheral. 

For both the central and receiver applications, bonding is disabled in the proj.conf as follows : 

CONFIG_BT_BONDABLE=n

In that case, I can't understand why the BASS re-discovery would fail due to a security error error.

As mentioned above. This only happens when using the Nordic Soft Device controller or the Packetcraft controller. Using the Zephyr controller, the re-discovery works fine without this security problem. 

How can there be this security issue only when using those two controllers, and by using the Zephyr controller with the exact same configuration (bonding disabled etc.) it is fine?

Below are the logs from my central application when it re-connects. Thanks in advance for any help or suggestions. 

Disconnected from device EE:0B:7C:30:59:12 (random) (reason 0x3e)
About to connect to EE:0B:7C:30:59:12
Connection pending..
Successfully connected to device EE:0B:7C:30:59:12 (random)
Now discovering..
[00:01:04.517,425] <wrn> bt_gatt: gatt_exchange_mtu_func: conn 0x200018c8 err 0x0e
[00:01:04.517,456] <dbg> bt_bap_broadcast_assistant: service_discover_func: Could not discover BASS
Error! BASS discover failed (-6)

    

[ovrebekk]

Hi Paul

Thanks for the update. 

Like mentioned earlier we haven't tested the Packetcraft controller with a broadcast stream and an ACL connection concurrently, and it is quite common to see instability issues when using it outside the uses cases for which it was designed. 

I will set aside some time to test this in order to try and figure out what is going on, and if there is something that can be done to improve reliability, but unfortunately I won't be able to start this work until next week. 

I will get back to you as soon as I have some test results to share. 

Feel free to update the case if you make any new discoveries in the mean time

Best regards
Torbjørn

[muli]

Hi ovrebekk 

The thing is, the Packetcraft controller when used with the Zephyr broadcast_audio_sink, it doesn't disconnect at all when it's connected to my Broadcast Assistant. 

The disconnecting is definitely an issue in my case, but it's not in fact the main blocker for me as my Broadcast Assistant has an auto re-connect feature which re-connects successfully.

However, it fails to re-discover the BASS then due to BT_HCI_ERR_INSUFFICIENT_SECURITY.

What's frustrating is that the re-discovery only fails when using the Packetcraft controller or Soft Device controller on the Broadcast Assistant, but not when using the Zephyr controller.

I could just use the Zephyr controller in that case, but it doesn't support PAST:)

Thanks,

Paul

[muli]

I'm attaching a zip here anyways of the latest Nordic application with the ability for the receiver to connect to a central.   

nrf5340_audio.zip

[ovrebekk]

Hi Paul

Thanks for sharing the code. I will set aside some time to test it next week. 

In the mean time please have a great weekend

Best regards
Torbjørn

[ovrebekk]

Hi again

I got some input from one of the audio developers, who did some testing attempting to run broadcasting and a peripheral connection in parallel. He was able to make it work using the Packetcraft controller, but thinks it might be critical how the ACL connection is used in order for the scheduling to succeed. 

He provided the following advice: 

1. Try not to do BIS and BLE at the same time, but one at a time. In order to configure the device stop the BIS broadcast first, finish configuration, and then restart BIS.
2. Try to use fixed connection parameters (don't do connection parameter update automatically), and set ACL interval to 40ms or 80ms (should be 4 times of ISO interval). 
3. In our testing we do all the Bluetooth GAP/GATT procedures step by step, rather than running multiple in parallel using the auto procedures from Zephyr. 
   In other words we establish the connection first, in connection callback we trigger security update, in security update callback we trigger the MTU exchange, and so forth. By doing this, we can make sure all the link layer procedures occur in sequence, which is less likely to cause issues for the controller. 
4. Please run a test using the latest NCS version, there might be some more improvements there. 

Best regards
Torbjørn