At the core of Bluetooth wireless technology lies the Bluetooth protocol stack – a layered architecture that defines how Bluetooth devices communicate with each other. This multi-layer stack governs everything from radio management to data exchange and application profiles. Let’s dive deeper into each layer’s roles and responsibilities.
Radio Layer This lowermost layer handles the transmission and reception of radio signals in the 2.4GHz ISM band. It defines the physical radio channel characteristics like modulation schemes, channel arrangement, and transmit power levels. Different Bluetooth versions use different radio configurations. For example, Bluetooth Low Energy uses two modulation schemes – uncoded GFSK for advertising packets and coded DPSK for data.
Baseband Resource Manager Sitting above the radio layer, the baseband resource manager is responsible for managing the physical radio channels and links. It handles critical procedures like device discovery, link formation, connection state management, and security protocols for authentication and encryption. The baseband defines two fundamental roles – master and slave, along with rules for a Bluetooth piconet topology.
Link Controller The link controller implements the baseband specification and works closely with the link manager to control the baseband hardware. It handles operations like active/sleep mode switching to optimize power. Error checking is also done at this layer through CRC and ARQ schemes.
Link Manager The link manager sets up logical links, handles control and negotiation of link parameters like quality of service requirements. It defines connection states, modes, and procedures for SCO and ACL logical transports. Encryption, role switch and hold mode operations are also initiated by the link manager.
L2CAP The Logical Link Control and Adaptation Protocol layer provides multiplexing capabilities to enable multiple applications to run concurrently over the air interface. It segments data from higher layers into baseband packets and reassembles packets at the receiving end. L2CAP provides guaranteed service for time-sensitive applications like audio.
SDP The Service Discovery Protocol allows Bluetooth devices to discover services offered by other devices and determine their characteristics, like requirements for connecting to them. It defines service attribute requests and responses.
RFCOMM This cable replacement protocol emulates a serial port and enables binary data transport. It is based on the ETSI TS 07.10 standard and facilitates legacy RS-232 connections over the L2CAP layer.
Application Layer The topmost layer comprises adopted protocols, profiles and APIs that enable development of Bluetooth applications. Profiles define specifications for common Bluetooth use cases like headsets, file transfer, networking etc. Well-known protocols like PPP for networking and OBEX for object exchange reside here.
Overall, the Bluetooth protocol stack defines a highly structured layout. Lower layers handle radio control while higher layers implement data exchange and application frameworks. This design enables robust connectivity and a wide range of wireless use cases across different Bluetooth versions. The stack is expertly crafted to preserve backwards compatibility while incorporating new enhanced protocols when needed.
