Empty Scan Response Handling

[Matt Barr]

Hello All,

I have a basic question about empty scan response operation with the ADV_IND PDU. When I set advertising data as follows:

    err_code = ble_advdata_set(&advdata, NULL);

is the central somehow informed that there is no scan response data so that it has the option of not issuing a scan request, or does the central have to determine this by issuing a scan request and seeing that the scan response data length is 0?

Looking at the standard I did not see a defined way to specify an empty scan response in the 16-bit advertising channel PDU header, but this seems quite possible (unused RxAdd bit for example) and I wanted to make sure I haven't missed something.

Thanks and Regards, Matt

[David Edwin]

There is no method by which the scanner can determine that the SCAN_RESPONSE is not present in an ADV_IND (advertising packet), so a scan request will be sent and a blank scan response is sent back to the scanner.

Do you wish to save power ? I would suggest that you reduce the size of the ADV_IND packet and place the bulk of your advertising in the SCAN_RESPONSE. Since the number of ADV_IND packet will outnumber the SCAN RESPONSE packets by a very large margin you will save power by making the ADV_IND as small as possible.

[David Edwin]

The central runs a active scanner so the ADV_INDs are received and SCAN_REQUEST is sent and SCAN_RESPONSE received and then the data is sent to the application. I.e. The data in the ADV_IND and the SCAN RESPONSE is should then be sent to the application together or not at all. This is the typical behaviour on a central like a iOS device or Android device. So typically there is no chance of an ADV_IND from one device getting mixed with the SCAN RESPONSE of another