BLE scan request

[Roei]

Hi,

I understand that scan request allows the broadcaster to send additional advertising data. Does it send the additional data via data channels? Is it related to secondary advertisement?

Thanks!

[Heidi-Irene Harvey Sollie]

Hi!

Yes, a scan request prompts a scan response from the peripheral, where you can put additional advertising data.

Out of the 40 RF channels in BLE, three of them (channels 37, 38, and 39) are the primary advertising channels while the remaining 37 are used for data transfer during a connection, but are also called the secondary advertising channels.

When using extended advertisement, you have the option to offload the scan request and response to the secondary channel but you don't necessarily have to do it. But to answer your question, the additional data (the scan response) is sent on the same channel as the scan request is received. 

See How Bluetooth Low Energy Works: Advertisements (Part 1) for more information.

Best regards,

Heidi

[Roei]

Thanks!

Can you please tell me how much data can an advertiser additionally send on scan response?

And how much data can an advertiser additionally send on secondary advertisement?

[Heidi-Irene Harvey Sollie]

Hi!

Roei said:

Can you please tell me how much data can an advertiser additionally send on scan response?

The scan response packet (SCAN_RSP) can carry up to 31 bytes of data.

Roei said:

And how much data can an advertiser additionally send on secondary advertisement?

When sending a scan response on the secondary advertising channel (AUX_SCAN_RSP), the package body is in the Common Extended Advertising Payload format, which can carry up to 251 bytes, or even chain packets, which increases the maximum size further.