BLE - GATT and characteristics

[Roei]

Hi,

I understand that Attribute protocol supports commands, requests, responses, notifications and indications.

Can you please tell me if those packets are sent with the characteristics, which contains the data? Or separately?

Thanks!

[Susheel Nuguru]

The ATT packets can contain value also but depends on what att packet you are sending.

For a characteristic, there are two attributes in it, one is for characteristic declaration and the other is for the characteristic actual value/data. So to transfer a full characteristic, you need to two attributes to be transferred to the peer.

[Roei]

Thanks!

What about UART service? I assume that when one side sends notification about updating a characteristics, the updated characteristics itself should be sent with the notification, right?

[Susheel Nuguru]

Yes, the notification  The Handle Value Notification  is in itself a standard BLE PDU with the ATT opcode set to notification. I recommend that you test out the UART example and connect the the BLE sniffer so that you can look into the packet structures in details. BLe sniffer can answer your most of the questions regarding packet formats and what is send in the notification is sent.

[Susheel Nuguru]

FYI, found this thread which might be of interest to you.