Logical Link Control and Adaptation Protocol (L2CAP) takes data from higher layers of the Bluetooth stack and from applications and sends it over the lower layers of the stack. L2CAP passes packets either to the Host Controller Interface (HCI), or in a host-less system, L2CAP passes packets directly to the Link Manager (LM).
Figure 9–1 shows L2CAP’s position in the Bluetooth stack for the cases with and without a Host Controller Interface. Note that L2CAP transfers data, not audio (though protocols such as voice over IP are regarded as data and would use L2CAP packets if transferred over a Bluetooth system).
L2CAP has many functions: