This informational series will cover all of the basics of Bluetooth Low Energy. Including some solutions offered in the BLE space. Classic Bluetooth was designed to replace cables and covers many protocols with speeds increasing in new versions.
2. PHASE LAYER
3. LINK LAYER ADVERTISING
4. LINK LAYER CONNECTION
5. LINK LAYER CONNECTION MANAGEMENT
HCI, or host controller interface, was designed to be the interface between the host and the controller. Hence, a physical interface is integrated in the specs, but nowadays it is not practically used as most modern BLE solutions integrate the hos and controller in a single package.
L2CAP is simply a multiplexing layer which has multiple channels. A channel is a single sequence of packets, from and to a single pair of services and a single device. Between two devices, there can be multiple channels active at the same time. A L2CAP enables BLE to multiplex three different channels and also enables segmentation and reassembly of packets that are larger than the underlying radio can deliver.