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The Bluetooth stack

Like many other communications technologies, Bluetooth is composed of a hierarchy of components, referred to as a stack. The stack is shown below: The Bluetooth Host Controller components provide the lower-level of the stack, which are typically implemented in hardware, and to which applications (or services as providers of particulary functionality over Bluetooth are called) do not have direct acccess.

The Bluetooth Host components allow applications to send or receive data over a Bluetooth link, or to configure the link:

RFCOMM allows an application to treat a Bluetooth link in a similiar way as if it were communicating over a serial port. This is used to support legacy protocols.

The Logical Link Control And Adaptation Protocol (L2CAP) allows finer-grained control of the link. It controls how multiple users of the link are multiplexed together, handles packet segmentation and reassembly, and conveys quality of service information. It is the usual choice for applications.

The Service Discovery Protocol (SDP) is used for locating and describing services provided by or available through a Bluetooth device. Applications typically use it when they are setting up communications to another Bluetooth device.

The Host Controller Interface (HCI) driver packages the higher level components to communicate with the hardware.