What are the conditions for sending a scan request?

RE: What are the conditions for sending a scan request?

run_ar — Wed, 05 Jan 2022 08:07:40 GMT

Sorry for not replying sooner. Answering this is speculations from my side, as I do not know how the phone is operating. But the phone would have to time multiplex Bluetooth LE, Bluetooth EDR, WiFi and LTE. So it might not prioritize sending scan responses. Another possibility could be that it is saving power by only sending the advertisement packet, or selectively responding to scan requests.

RE: What are the conditions for sending a scan request?

sdi_kei — Mon, 15 Nov 2021 08:12:04 GMT

Hello.

But it could be that android does not reply to all scan requests for some reason.

Do you know why this is happening?
I'm sorry you don't have time, but I'd be happy if you could tell me.

RE: What are the conditions for sending a scan request?

sdi_kei — Wed, 06 Oct 2021 06:31:55 GMT

Hello.

Thank you for the project.
Please check your android when you have time.
It is said that android may not reply to the scan request for some reason, but is this unclear?

Best Regards.

RE: What are the conditions for sending a scan request?

run_ar — Fri, 01 Oct 2021 09:09:53 GMT

Hi,

Unfortunately I have not had time to test with android this week. But it could be that android does not reply to all scan requests for some reason.

The projects I used for my test are "ble_central\ble_app_uart_c"

devzone.nordicsemi.com/.../8585.ble_5F00_app_5F00_uart_5F00_c.zip

And ble_peripheral\ble_app_uart

devzone.nordicsemi.com/.../8407.ble_5F00_app_5F00_uart.zip

SDK 17.1.0, and I only tested the pca10040\s132\ses projects.

RE: What are the conditions for sending a scan request?

sdi_kei — Mon, 27 Sep 2021 01:34:12 GMT

Hello.

Thank you for your investigation.
The amount of failure is very small at 1%.
It was quite different from the results I posted earlier.

If you have time or equipment, I would like you to conduct a survey with a different Bluetooth version (ver 4.2, etc.) or a survey using an Android device.
The purpose is to see if the amount of failures has decreased because both were nrf52832.

You said that you changed the SDK example. Which example did you use?

I hope you'll tell me.

Best Regards.

RE: What are the conditions for sending a scan request?

run_ar — Fri, 24 Sep 2021 11:20:15 GMT

Hi,

It took some time to modify the SDK examples to log this and perform the testing. Testing is performed at my home office without a RF chamber. Both scanner and advertiser is a nrf52832 DK.

In this log you see 22 hits (search in notepad++) for:
<info> app: scan match 7E32890DE6DC

<info> app: scan match 7E32890DE6DC

And there is 2100 hits for:

<info> app: scan match 7E32890DE6DC

<info> app: scan req: 01

Meaning the amount of failing active scans using a nRF52832 as active scanner is close to 1%.

devzone.nordicsemi.com/.../Active-scanning-RTT-log.txt

RE: What are the conditions for sending a scan request?

sdi_kei — Tue, 21 Sep 2021 00:30:28 GMT

Hello.

Thank you for your investigation.
I am looking forward to the results.

Best Regards.

RE: What are the conditions for sending a scan request?

run_ar — Fri, 17 Sep 2021 14:06:10 GMT

Sorry for the late reply, unfortunately I did not have time to test it this week. but this case is first on my list now, so assuming I will be able to test it next week.

Br,

RE: What are the conditions for sending a scan request?

sdi_kei — Thu, 09 Sep 2021 04:46:21 GMT

Hello.

I want you to check. This is because if you can receive "Scan Response data" every time you receive "Advertising data", you know that my software should be set up like the FW you used.

Best Regards.

RE: What are the conditions for sending a scan request?

run_ar — Wed, 11 Aug 2021 08:20:02 GMT

I meant, that to check that this is not caused by something in your implementation, you could try to place the scanner and advertiser in an RF chamber to see if this improves. Not sure it would make much sense for me to test it here with different fw.

RE: What are the conditions for sending a scan request?

sdi_kei — Wed, 21 Jul 2021 01:55:51 GMT

Hello.

[quote userid="2112" url="~/f/nordic-q-a/76886/what-are-the-conditions-for-sending-a-scan-request/319459#319459"]Just to be sure it is not another issue you could place the scanner and advertiser in an RF chamber to see if you still have problems.[/quote]

Will you make sure it's not another issue for me?
I tried to check "core spec 4.4.3.2 Active scanning" but couldn't find it. Could you give me a link?
Also, is the backoff procedure in the SDK source?

Thank you.

RE: What are the conditions for sending a scan request?

run_ar — Fri, 09 Jul 2021 22:11:18 GMT

I am afraid you just have to keep trying (i.e. scan multiple times). Just to be sure it is not another issue you could place the scanner and advertiser in an RF chamber to see if you still have problems.

Scanners have a backoff routine, but it can still take a few attempts before you are successfull. see core spec 4.4.3.2 Active scanning

The backoff procedure uses two parameters, backoffCount and upperLimit, to
restrict the number of scan request PDUs sent when collisions occur on scan
response PDUs. Upon entering the Scanning State, the upperLimit and
backoffCount are set to one....

RE: What are the conditions for sending a scan request?

sdi_kei — Fri, 09 Jul 2021 03:01:35 GMT

Hello.

Since active was 1, it did not solve the problem that Scan Response did not return.

Is there a way to solve this problem?
Assuming that you will actually use it, I think there are many active Centrals around you. Is there no choice but to start over from Advertise reception until Scan Response can be received?

Thank you.

RE: What are the conditions for sending a scan request?

run_ar — Thu, 08 Jul 2021 11:45:23 GMT

Hi,

Check ble_gap_scan_params_t and make sure that

uint8_t

active: 1

This will enable active scanning. There might still be other active scanners in the area. These will potentially send a scan request at the same time as you do, potentially creating a CRC error on the Advertiser, which will cause it to not send the scan response.

RE: What are the conditions for sending a scan request?

sdi_kei — Thu, 08 Jul 2021 10:46:19 GMT

Hello.

You must send a Scan Request from Central to have the advertisement send you a Scan Response.
I want to set Central to issue a Scan Request, what should I do?

Thank you.

RE: What are the conditions for sending a scan request?

run_ar — Thu, 08 Jul 2021 10:33:55 GMT

The advertisement packet and scan response packets are two separate packages. First the scanner must receive the advertisement packet, then it must send a scan request, So the advertiser will only send the scan response if it first receives a scan request

RE: What are the conditions for sending a scan request?

sdi_kei — Thu, 08 Jul 2021 04:47:24 GMT

Hello.

I don't know the sample source from which my code is based.
As a confirmation method, NRF_BLE_SCAN_EVT_FILTER_MATCH of scan_evt_handler is confirmed whether scan_response is 1. (p_scan_evt-> params.filter_match.p_adv_report-> type.scan_response)
Therefore, I don't use ellisys sniffer.

[quote userid="2112" url="~/f/nordic-q-a/76886/what-are-the-conditions-for-sending-a-scan-request/318987#318987"] It could be that there are also other scanners performing active scanning, which is "blocking" the scan requests from your scanner.[/quote]

In other words, is it not possible to get the advertisement of the Android device because it was picked up by two scans and both of them are making requests?

Isn't the scan response sent by the data contained in the advertisement packet?

Thank you.

RE: What are the conditions for sending a scan request?

run_ar — Wed, 07 Jul 2021 12:59:05 GMT

Hi,

Would you by any chance have an ellisys sniffer so you can capture the on air traffic? Or as an alternative place the scanner and advertiser in an RF chamber? It could be that there are also other scanners performing active scanning, which is "blocking" the scan requests from your scanner.

RE: What are the conditions for sending a scan request?

sdi_kei — Mon, 05 Jul 2021 00:15:04 GMT

Hello.

Regarding the Scan time setting, interval is set to 0x320 (800ms) and window is set to 0x190 (400ms).
When the reception frequency of 4000ms was measured, the reception frequency of Advertise data was 8 times and the reception frequency of Scan Response was 2 times.
The device Advertise cycle is 100ms. Advertise parameters are Flags, 128bit UUID and Manufacturer Data, and Scan parameters are 128bit UUID and Manufacturer Data.

Thank you.

RE: What are the conditions for sending a scan request?

Joakim Jakobsen — Fri, 02 Jul 2021 16:00:24 GMT

Hi.

[quote user=""]Currently, after receiving "Advertising data", "Scan Response data" can be obtained on rare occasions.[/quote]

What do you mean by rare occasions?

How often do you receive the advertising data, and how often do you receive the scan response data?

What are the advertising and scan parameters for your devices?

Br,
Joakim