Fast connecting to a bonded device

RE: Fast connecting to a bonded device

Einar Thorsrud — Tue, 28 Sep 2021 12:58:05 GMT

I understand. That seems to be the only option for now.

In case other find this thread, it turns out that the Zephyr Bluetooth controller implementation now takes 4 connection events to secure the link, due to control procedure handling moved to lower priority Upper Link Layer (previously it was 3 connection events).

RE: Fast connecting to a bonded device

db_lw — Tue, 28 Sep 2021 12:29:18 GMT

Ok, thank you for your help. I will then not use bonding at the moment.

RE: Fast connecting to a bonded device

Einar Thorsrud — Mon, 27 Sep 2021 10:28:23 GMT

Hi David,

I tested a similar setup on my end but with 1 Mbps and see the same. I will check more with the stack team, but it looks like it is difficult to speed this up.

RE: Fast connecting to a bonded device

db_lw — Mon, 27 Sep 2021 07:51:04 GMT

Hi Einar,

thanks for your response. Ok, I guess then I have to reconsider using bonding for this application.

[quote userid="7377" url="~/f/nordic-q-a/79897/fast-connecting-to-a-bonded-device/331129#331129"]Could you test that just for comparison?[/quote]

I probably won't do that because in this case the use of coded phy is mandatory.

Best regards,
David

RE: Fast connecting to a bonded device

Einar Thorsrud — Fri, 24 Sep 2021 14:49:45 GMT

Hi David,

The sniffer trace shows well what happens on air, and there are a few connection events between LL_ENC_REQ/RSP and LL_START_ENC_REQ/RSP. Unfortunately I was not able to conclude if it is possible to reduce the time more or not today, so I will have to get back to you early next week.

Edit: I discussed a bit with the BT stack team and they did not see much room for improvement, but may be that it could be slightly faster with 1 Mbps instead of coded phy. Could you test that just for comparison?

RE: Fast connecting to a bonded device

db_lw — Thu, 23 Sep 2021 12:47:21 GMT

I attached my sniffer trace. Maybe you can see something that's causing a delay.

Edit: Sniffer trace with key for decryption.

devzone.nordicsemi.com/.../ble_5F00_lesc_5F00_conn_5F00_already_5F00_bonded_5F00_with_5F00_key.pcapng

RE: Fast connecting to a bonded device

db_lw — Thu, 23 Sep 2021 12:25:25 GMT

Hi Einar,

thanks for your reply.

[quote userid="7377" url="~/f/nordic-q-a/79897/fast-connecting-to-a-bonded-device/330777#330777"]Can you make a sniffer trace showing the packet exchange on air?[/quote]

I wasn't aware that the sniffer is able to capture Coded PHY. The last time I check it wasn't supported. I will capture a sniffer trace.

[quote userid="7377" url="~/f/nordic-q-a/79897/fast-connecting-to-a-bonded-device/330777#330777"]Do you call bt_conn_set_security() immediately after the connection was established?[/quote]

I would say it's immediately. I call it in the callback function that is registered with bt_conn_cb_register().

Best regards,
David

RE: Fast connecting to a bonded device

Einar Thorsrud — Thu, 23 Sep 2021 09:14:29 GMT

Hi David,

Just connecting and encrypting an already bonded link should be fast. Can you make a sniffer trace showing the packet exchange on air? Do you call bt_conn_set_security() immediately after the connection was established?