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When is a custom GATT profile recommended?

Mahesh Venkitachalam

I am currently developing an IoT device using nRF8001 which needs to report gas concentration obtained from a sensor. I have looked through the standard GATT profiles, and I don't see anything I can use directly. I was curious if it's common practice for products to create their own custom GATT profiles.

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    Hi electronut,

    I believe then it's more question of interoperability. If you want to rely on different (central) apps connecting to your device and reading/showing the data then you are interested into standard GATT Services defined by BT SIG (e.g. if you implement Battery Service then many existing central apps can display it even they do not understand the main purpose of your peripheral device). If your main architecture is based on peripheral and specific matching central app then you do not care and then you can freely start designing custom services because all BT Smart APIs on mobiles (Android, iOS) and PCs (Win 8.1/10) support search and use of custom GATT Services/Characteristics.

    Main rules for such custom design might be:

    • Create simple services per "interface" or "feature" you offer on server (peripheral) side.
    • Remember that every new service and characteristic/descriptor make generic Service Discovery procedure slower (which might be an issue if you are connecting for every transaction).
    • Also remember that even GATT handle space is usually not an issue (65k slots) implementation of BLE stack in embedded systems might have limitations and overloading stack just increases probability of issues in the field.

    There are some rules explained at the slides 321-395 of the original BLE training delivered by BT SIG in 2010 here (member login required): www.bluetooth.org/.../DownloadDoc.ashx

    Cheers Jan

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    Hi electronut,

    I believe then it's more question of interoperability. If you want to rely on different (central) apps connecting to your device and reading/showing the data then you are interested into standard GATT Services defined by BT SIG (e.g. if you implement Battery Service then many existing central apps can display it even they do not understand the main purpose of your peripheral device). If your main architecture is based on peripheral and specific matching central app then you do not care and then you can freely start designing custom services because all BT Smart APIs on mobiles (Android, iOS) and PCs (Win 8.1/10) support search and use of custom GATT Services/Characteristics.

    Main rules for such custom design might be:

    • Create simple services per "interface" or "feature" you offer on server (peripheral) side.
    • Remember that every new service and characteristic/descriptor make generic Service Discovery procedure slower (which might be an issue if you are connecting for every transaction).
    • Also remember that even GATT handle space is usually not an issue (65k slots) implementation of BLE stack in embedded systems might have limitations and overloading stack just increases probability of issues in the field.

    There are some rules explained at the slides 321-395 of the original BLE training delivered by BT SIG in 2010 here (member login required): www.bluetooth.org/.../DownloadDoc.ashx

    Cheers Jan

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