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  • Case ID: 292751
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ScanReq backoff mechanism

jermi

Hi nordic:

     As shown in the figure below, I see that the BLE protocol standard mentions the ScanReq backoff mechanism. Does NORDIC implement it?

    

jermi.jin

thanks!!

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  • 0

    Hello jermi.jin,

    I would definitely assume so since this is part of the BT Core specification, and so it is a requirement for all qualified BLE controllers - but I can not seem to find that it is explicitly mentioned in the SoftDevice documentation at the moment. Do you require an explicit confirmation of this?
    The backoff mechanism is something that is be handled by the SoftDevice or SoftDevice Controller for you directly, so it is not something you would have to enable or actively add during your development.

    Best regards,
    Karl

  • 0 in reply to Karl Ylvisaker

    Hello Karl ：

    I now have many (more than 100) terminal slaves broadcasting at the same time, and several masters scan the information of the slaves, and sometimes the information of some slaves cannot be collected, so I need to know the information:

    How long is the backoff period? How is it achieved? If there are two hosts scanning at the same time, what is the probability of collision? What about 5? If Scanner B receives the ScanResp triggered by A during the backoff period, how does B handle it?
    In addition, I noticed that on the online-power-profiler, the RX time is only 60us. If there is a back-off mechanism, this receiving time is not enough at all. How do you understand it?

  • 0 in reply to jermi

    Hello,

    Thank you for the additional information.

    jermi said:
    How long is the backoff period? How is it achieved? If there are two hosts scanning at the same time, what is the probability of collision? What about 5?

    This is all detailed in the section of the Core Specification that you linked - 4.4.3.2, on the page following your screenshot. The backoff period will depend on the advertising interval. Please see page 2772 of the Bluetooth Core specification v5.3, and let me know if you have any questions, or if anything is still unclear! :) 

    I will also forward these questions to the developers, to have definitive confirmation that it is implemented exactly as written in section 4.4.3.2 of the Bluetooth Core specification v5.3.

    jermi said:
    If Scanner B receives the ScanResp triggered by A during the backoff period, how does B handle it?

    Scan responses are directed, so B would not record the scan response triggered by A, since it is not directed at B, and B did not expect this scan response.

    Best regards,
    Karl

  • 0 in reply to Karl Ylvisaker

    Hello again, Jermi

    I just received word from the developers that the backoff mechanism is implemented as detailed in the core specification.

    Best regards,
    Karl

  • 0 in reply to Karl Ylvisaker

    Hi kral:

       thank your replay！！

    jermi.jin

     

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