GATT notification packets per connection interval on nRF Connect SDK

RE: GATT notification packets per connection interval on nRF Connect SDK

ebmmy — Mon, 31 Mar 2025 14:39:14 GMT

Thanks for the additional info !

RE: GATT notification packets per connection interval on nRF Connect SDK

Sigurd — Thu, 27 Mar 2025 20:23:06 GMT

Hi!

[quote user="ebmmy"]What is considered a NAK within the context of the QoS event? Is it triggered by the central receiving a packet requesting retransmission? Is a dropped packet also considered a NAK?[/quote]

https://docs.nordicsemi.com/bundle/nrfxlib-apis-2.9.0/page/structsdc_hci_subevent_vs_qos_conn_event_report_t.html

It's defined as "Number of received Negative Acknowledges from the peer during the connection event."

[quote user="ebmmy"]Is my understanding correct that the SoftDevice controller (on the nRF54 peripheral) could, under certain circumstances, interrupt a connection event with the central to prioritize an advertising or scanning event?[/quote]

Correct, see this link: https://docs.nordicsemi.com/bundle/ncs-latest/page/nrfxlib/softdevice_controller/doc/scheduling.html

RE: GATT notification packets per connection interval on nRF Connect SDK

ebmmy — Thu, 27 Mar 2025 14:50:02 GMT

Hello,

Thanks for your suggestions. I think you've pointed me in the right direction. It appears the peripheral (nRF54) was also scanning and advertising, which likely caused the scheduler on the peripheral side to close the connection event earlier than expected.

Without advertising or scanning on the peripheral side, I'm now able to send up to 15 packets per connection event in a quite stable manner.

This has raised a couple of questions for me:

What is considered a NAK within the context of the QoS event? Is it triggered by the central receiving a packet requesting retransmission? Is a dropped packet also considered a NAK?
Is my understanding correct that the SoftDevice controller (on the nRF54 peripheral) could, under certain circumstances, interrupt a connection event with the central to prioritize an advertising or scanning event?

Thank you for your support

Best regards

RE: GATT notification packets per connection interval on nRF Connect SDK

Jakob Ruhe — Wed, 26 Mar 2025 21:05:11 GMT

Hello,

I have no experience of the QoS event.

But to achieve high speed you can use 2 Mbit/s data rate. Perhaps you are already doing that. I also guess you have had a look at the is throughput example which can be good to fetch inspiration from, and to perform throughput tests with.

Within a single Connection Event the nodes can exchange packets as long as either of the Controllers have packets available and there is time left until something else (for example a new Connection Event) should take place.

That motivates a long Connection Event Interval (because we get less interruptions).

However. As soon as a packet is dropped (or is corrupt), no more communication can take place in that Connection Event. Both parties have to wait for the next Connection Event and continue again from the last packet that failed.

That motivates shorter Connection Event Intervals.

So, if you are experiencing that packets get dropped, because of low RSSI or disturbance, you may try to use a lower the Connection Event Interval. Try with 10 ms and 20 ms for example.