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ble connection sequence

user102105

HI,

I am developing an application which requires BLE connection. I am concerned about the energy consumed by the device during the connection.

I understand that once the connection is established there will be EXHANGE MTU and Discovery sequence ? Is this mandatory ? How can we keep the connection sequence to minimal ?

I am attaching the log file from sniffer and I observe many packets between master(nRF Connect) and slave ? Is this normal ? Can we optimize this if we develop our own master/client application?

  • 0

    Hello!

    When establishing a connection some packets will be sent back and forth between the central and peripheral to configure the connection properly.

    In the simplest case this could be just a connection request packet from the central to the peripheral, but often more packet exchanges are needed.

    For example an MTU exchange, which sets the Maximum Transmission Unit, allowing for more data per packet.

    The discovery sequence on the other hand is done before establishing a connection, and involves the central unit choosing what advertising peripheral to connect to.

    All this is mandatory to set up a connection, but shouldn't be of great concern when it comes to energy consumption, as it only happens once at the beginning of a connection.

    Then there are all the empty packets you have observed being sent between the central and peripheral.

    These are sent regularly in order to keep the BLE connection alive, at a frequency set by the connection interval, which is decided by the central in the initial connection request.

    The connection interval seems to be set to a low value in your application since these packets are sent pretty frequently. It can be set to as high as a few seconds I believe.

    Setting a higher connection interval will likely make your application consume less power since it's sending fewer packets, but you might also find your application less responsive if you set it too high.

    Hope this clears up some of your questions.

    Best regards,

    Einar

  • 0 in reply to user111520

    Hi, 

    Thank you for your reply.

    user111520 said:

    The discovery sequence on the other hand is done before establishing a connection, and involves the central unit choosing what advertising peripheral to connect to.

    Oh sorry, I meant GATT database discovery which happens after the connection. Is this really needed if the client already knows the UUID of the characteristic being used ? Can client read/write using the UUID without the handle ?

  • 0 in reply to user102105

    Hi,

    There are many options in the Zephyr Bluetooth GATT API, maybe this function can suit your needs?

    What code are you currently running? Have you based your application on a sample?

    -Einar

  • 0 in reply to user111520
    user111520 said:

    What code are you currently running? Have you based your application on a sample?

    \examples\ble_peripheral\ble_app_template - My application is based on ble_app_template.

    I am just analysing the energy consumed during the connection.  

  • 0 in reply to user102105

    Right, I assumed you were using NCS, but you're using the nRF5 SDK?

    The ble app template is for an advertising peripheral, so I assume you're using nRF Connect as your central unit when testing to connect to your devkit?

    In that case, your DK will only do what the central tells it to, it's always the central unit that initiates things like GATT database discovery etc, so if you want to test with your own custom application at both ends that might be easier to do with two devkits for example.

    Also, as I already mentioned, this initial setup communication is not what you should be worried about when it comes to your application's power consumption.

    -Einar

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