Glossary

A2DP

Advanced Audio Distribution Profile. A2DP is used for audio streaming between a computer and audio capable device. An A2DP device may be a source or a sink.

A2DP supports different codecs depending on the type of audio link being established. The only mandatory codec is SBC.

AVCTP

Audio/Video Control Transport Protocol. The protocol used to carry the commands that form part of the AVRCP profile.

AVRCP

Audio Video Remote Control Profile. AVRCP allows for both an originator (i.e., controller) and recipient (i.e., controllee) to send or receive AVRCP commands. All AVRCP capable devices advertise which commands they support during the link establishment.

Note: an AVCTP link is established automatically by bluez whenever a device connection is made (e.g., audio) provided the Control profile is enabled as part of your audio.conf bluetooth settings.

SBC

Low complexity subband coding. The SBC codec is a mandatory requirement for A2DP capable devices. It employs a psycho-acoustic model in order to compress frequency bands present in an audio source in accordance with human hearing sensitivity. The compression algorithm is lossy which means that the original source is never constructed perfectly once it has been through the encoding/decoding process.

SDP

Service Discovery Protocol. SDP is used in order for a host to discover the services provided by a device. SDP uses an attribute identification based scheme with a generic set of attributes being applicable to all classes and types of devices and service-specific attributes in accordance with the :term:`UUID`s supported by the device.

UUID

Universally Unique Identifier. A UUID is a 128-bit number used to represent a service, protocol or other attribute as part of the bluetooth standard. UUIDs generally take a 16-bit short-form that is derived from their 128-bit representation since, generally, no more than 65536 UUIDs are ever used simultaneously within the context of one application.

dbus

A message bus system providing a simple way for applications to talk to one another. Bluez provides dbus hooks allowing applications to establish bluetooth sessions and manage bluetooth hardware and devices.

bluez

Bluez provides the upper layers (i.e., above PHY) and management interface of the bluetooth protocol stack under Linux.

PHY

Physical layer. In bluetooth this refers to the radio (RF) channel which is operating in the 2.4GHz frequency band. The PHY employs coding/decoding and modulation/demodulation techiques to allow information to be sent over-the-air.

HFP

Hands-free profile. The service profile used by devices that support a hands-free mode of operation, such as, a mobile phone connected to a car.

HSP

Headset profile. The service profile used by bluetooth headphones or earpieces.

source

An entity capable of generating media content for streaming. For example, a music player.

sink

An entity capable of receiving media content for rendering. For example, a headset or speaker.

codec

An en(cod)er/d(ec)oder. A codec may be implemented in software or hardware and typically perform compression of the original source to a lower bit-rate prior to transmission and decompression back to the original bit-rate following reception. The algorithms employed may be lossy (meaning the original signal source is not reconstructed perfectly but is generally a good enough approximation not to be perceived) or lossless (meaning the original signal source is reconstructed perfectly).

adapter

A (bluetooth) adapter is a piece of physical hardware that allows a device to transmit and receive in accordance with the bluetooth standards. The adapter typically implements the PHY (i.e., physical layer).

device

A generic term referring to any piece of hardware that provides services over bluetooth.

transport

The transport or transport layer normally refers to the link layer (or L2) link that is established between two devices over bluetooth. It allows for bi-directional communications and employs error checksums and re-transmissions for improved reliability so that the application layer need not worry about this.

SCO

Synchronous Connection-Orientated.

ACL

Asynchronous Connection.

PCM

Pulse-coded Modulation.

HCI

Host controller interface. This is typically a serial link between the bluetooth stack and the bluetooth adapter and provides a standard interface such that different stack implementation can be easily plugged-in. It provides low-level commands for device setup, flow control, device discover, quality of service, physical links, authentication and encryption.