The Bluetooth LE Core system consists of a LE Host and a LE Controller. HCI defines a functional interface for bidirectional communication between Host and Controller.
SM defines procedures to manage pairing, authentication and encryption.

ATT defines the protocol between an ATT Server and an ATT Client for discovering, reading, and writing attributes.

GATT defines the hierarchy of services, characteristics, attributes, and higher level procedures for using ATT.

GAP defines the generic procedures related to advertising, scanning and connection. In addition, GAP defines different security levels and modes, and user interface standards, etc. There are four GAP roles: Broadcaster, Observer, Peripheral, and Central. A device may support multiple LE GAP roles.

A device can support one-to-one communication when in connected state. Each Peripheral communicates bidirectionally with Central on a separate LE connection.

Direction Finding enables devices to determine the direction of another device. There are two methods of Direction Finding: Angle of Arrival (AoA) and Angle of Departure (AoD).
A device consisting of an antenna array can use AoA method to determine the angle of arrival of another device by receiving direction finding enabled packets.
A device consisting of an antenna array can use AoD method to make its angle of departure detectable to another device by transmitting direction finding enabled packets.
Direction Finding supports connection-oriented and connectionless scenarios.

Broadcast Isochronous Stream (BIS) supports unidirectional, one-to-many isochronous communication among unconnected devices. BIS Receiver synchronizes with PA sent by BIS Broadcaster. Then BIS Receiver uses the BIS information from PA to synchronize with BIS Broadcaster. Once BIS synchronization is established, BIS Receiver can receive isochronous data from a BIS.