Bluetooth Low Energy Protocol Stack Basics
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SWRU271H–October 2010–Revised April 2019
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Overview
Advertisers transmit data without forming a Bluetooth Low Energy connection, while scanners receive the
data broadcasted by advertisers. An initiator is a device that responds to an advertiser by requesting to
connect. If the advertiser accepts, both the advertiser and initiator connect. When a device is in a
connected state, it is either a master or slave. The device that initiated the connection becomes the
master and the device that accepted the request becomes the slave. This layer is implemented in the
library code in the TI 1.5.x\ with the actual path defined by the SDK installer version, .
The host control interface (HCI) layer provides a means of communication between the host and controller
through a standardized interface. This layer can be implemented either through a software API, or by a
hardware interface such as UART, SPI, or USB. Device Information Service (Bluetooth Specification),
Version 1.0 (24-May-2011) specifies the standard HCI commands and events. The TI BLE Vendor
Specific HCI Reference Guide specifies the TI proprietary commands and events.
The link logical control and adaption protocol (L2CAP) layer provides data encapsulation services to the
upper layers, allowing for logical, end-to-end communication of data. For more information on TI's
implementation of the L2CAP layer, see Section 5.6.
The security manager (SM) layer defines the methods for pairing and key distribution, and provides
functions for the other layers of the protocol stack to securely connect with and exchange data with
another device. For more information on TI's implementation of the SM layer, see Section 5.4.
The GAP layer directly interfaces with the application and/or profiles to handle device discovery and
connection-related services for the device. GAP also handles the initiation of security features. For more
information on the GAP layer, see Section 5.2.
The attribute protocol (ATT) layer protocol lets a device expose certain pieces of data (attributes) to
another device.
The GATT layer is a service framework that defines the subprocedures for using ATT. GATT
subprocedures handle data communications between two devices in a Bluetooth Low Energy connection.
The application and profiles use GATT directly. For more information on the ATT and GATT layers, see
Section 5.5.
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