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Core Protocols


The Baseband and Link Control layer enables the physical RF link between Bluetooth forming a piconet. As the Bluetooth RF system is a Frequency-Hopping-Spread-Spectrum system, in simpler terms packets are transmitted in defined time slots on defined frequencies. This synchronizes the transmission hopping frequency and clock of different Bluetooth devices.

It provides two different kind of physical links with their corresponding baseband packets, Synchronous Connection-Oriented and Asynchronous Connectionless which can be transmitted in a multiplexing manner on the same RF link.Asynchronous Connectionless (ACL) packets are used for the transmission of data only while Synchronous Connection-Oriented can contain audio only or a combination of audio and data.

All audio and data packets can be provided with different levels of FEC or CRC error correction and can be encrypted. Furthermore, the different data types, including link management and control messages, are each allocated a special channel

Audio data can be transferred between one or more Bluetooth devices, making various usage models possible and audio data in SCO packets is routed directly to and from Baseband and it does not go through L2CAP. Audio model is relatively simple within Bluetooth; any two Bluetooth devices can send and receive audio data between each other just by opening an audio link.

Link Manager Protocol

The link manager protocol is responsible for link set-up between Bluetooth devices. This includes setting up of security functions like authentication and encryption by generating, exchanging and checking of link and encryption keys and the control and negotiation of baseband packet sizes. Furthermore it controls the power modes and duty cycles of the Bluetooth radio device, and the connection states of a Bluetooth unit in a piconet.

Logical Link Control and Adaptation Protocol

The Bluetooth logical link control and adaptation protocol (L2CAP) adapts upper layer protocols over the baseband. It can be thought to work in parallel with LMP in difference that L2CAP provides services to the upper layer when the payload data is never sent at LMP messages.

L2CAP provides connection-oriented and connectionless data services to the upper layer protocols with protocol multiplexing capability, segmentation and reassembly operation, and group abstractions. L2CAP permits higher-level protocols and applications to transmit and receive L2CAP data packets up to 64 kilobytes in length. Although the Baseband protocol provides the SCO and ACL link types,L2CAP is defined only for ACL links and no support for SCO links is specified in Bluetooth Specification 1.0.

Service Discovery Protocol

Discovery services are crucial part of the Bluetooth framework. These services provide the basis for all the usage models. Using SDP, device information, services and the characteristics of the services can be queried and after that, a connection between two or more Bluetooth devices can be established. SDP is defined in the Service Discovery Protocol specification.

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