The audio protocol belongs to the Bluetooth protocols, it is based directly on the baseband protocol and operates as a synchronous connection-oriented service, Synchronous Connection OrientedLink
(SCO). The audio protocol works in direct mode without other protocols and is used to operate headphones and earphones. The audio data is transmitted in parallel with other data and is provided with mechanisms for error correction. Since in Bluetooth the audio connection works as a direct connection, each Bluetooth station of another can transmit voice signals.