Bluetooth: Stack

: A standardized communications interface (typically UART, USB, or SPI) that allows the Host and Controller to communicate even if they are from different vendors. Key Layers and Protocols

This layer defines how pairing and encryption happen. It is responsible for generating the encryption keys and managing the security levels (e.g., "Just Works" pairing vs. Passkey entry) to ensure the connection is private. bluetooth stack

Used primarily in Classic Bluetooth, SDP allows a device to find out what services another device offers (e.g., "Does this laptop support audio output?"). "Does this laptop support audio output?").