CODEWITHSUNDEEP
bluetooth-lowenergygattbluetooth-gatt
drew covi
drew covi

Reputation: 891

Separate vs Combined Characteristics in one Gatt

We're trying to determine whether to use separate GATT characteristics or combine multiple properties into one custom characteristic.

The benefits of combining is fairly clear: one transaction, many properties.

But even with multiple characteristics (one property per), the transaction seems quick enough.

Is this entirely an arbitrary decision? Or are there best practices?

Upvotes: 1

Views: 151

Answers (1)

Youssif Saeed
Youssif Saeed

Reputation: 13295

This is highly relevant and depends on the system you're trying to implement. My recommendation is to go for many separate characteristics. The reason is that you will be simplifying the application both on the GATT server side (where all the characteristics are stored) and the GATT client side. For example, if you use multiple characteristics, this means that you have to add extra intelligence to your GATT client side to separate the data in those characteristics. If the data side is variable, then this will be even more complicated. If in the future you have to update this combined characteristic with new features, the task will probably be relatively more complex for both the client and the server side compared to having many characteristics as things will be more categorised and compartmentalised.

Another thing to consider is testing. When you create your GATT server application, you'd want to test it with one or many different GATT client implementations (e.g. iOS device, Linux machine, etc). For that, it will be a lot easier if the remote device is not getting a combined characteristic and trying to make sense of the data.

Finally, please note that as you said, the transaction in Bluetooth is relatively quick and you will not be getting a huge difference when using multiple characteristics vs one. The reason is that by default the characteristic length is 20 and the Bluetooth packet length is 27 (unless you're using a Bluetooth 4.2 feature known as Data Length Extension, which not all phones support). Therefore, even if you use characteristic lengths greater than 20, the Bluetooth stack/baseband will divide the characteristic into chunks and send them over air, therefore not achieving the improved throughput that you aimed for.

I hope this helps.

Upvotes: 2

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