With the wide adoption of smartphones and the attractive market for the Internet of Things (IOT) and other accessories, Bluetooth connectivity has made its way into many products and most people’s daily life. In the last five years there has likewise been rapid advances in the Bluetooth protocol and its integration in devices. Beyond the consumer applications most people think of when Bluetooth is mentioned, the technology has also proven its worth in the Industrial IoT (IIoT).
This post will serve as a small introduction to the technology behind the scenes.
Bluetooth Classic (1.0-3.0)
Most people’s first introduction to Bluetooth was the original classic protocol. The protocol was introduced as a short range wireless protocol primarily targeted at low power wire replacement. The protocol involved the use of one of the approved profiles so that devices could connect and function without custom drivers. An example of the most common profiles include:
Serial Port Profile (SPP)
Human Interface Device (HID)
Hands-Free Profile (HFP) and Headset Profile (HSP)
Advanced Audio Distribution Profile (A2DP)
A/V Remote Control Profile (AVRCP)
Most people probably have been exposed to Bluetooth mice and keyboards (HID), Headsets (HSP) and speakers or headphones (A2DP). Additionally devices could implement multiple profiles e.g. to combine audio and remote control.
The other notable portion of Bluetooth classic prior to 2.1 is the requirement to pair with limited input devices using a fixed 4 digit pin, typically 0000 or 1234 in order to establish a full connection.
Bluetooth 4.0 (Classic + Smart / LE)
Bluetooth 4.0 brought a major change to the Bluetooth specification with the introduction of Low Energy (LE) or Smart devices. Bluetooth Smart devices incorporated a new specific profile geared towards simple data exchange as well as simple secure pairing (SSP) introduced in 2.1. Device manufactures could also choose to design Smart only devices, eliminating the need to maintain compatibility with the classic protocol. Smart only implementations greatly reduced the protocol stack and allowed Bluetooth to be implemented on smaller, cheaper and lower power chips. Bluetooth 4.0 was first supported on the iPhone4s at the end of 2011 and made its way into most other consumer electronics over the next year. The unique features of Bluetooth Smart are outlined below.
GATT (Generic Attribute Profile)
The profile introduced with Bluetooth smart was the GATT profile. This was an expansion of the classic ATT profile and allows the discovery and transfer of data through Services and Characteristics. Additionally the Bluetooth SIG defines many default Services and Characteristics for health and consumer devices to improve cross-compatibility between devices and software.
Services
Services are collections of characteristics that share a common function. Examples from the default services include Device Information (180A), Battery Service (180F) and Health Thermometer (1809).
Characteristics
Characteristics are individual properties within a service that provide data to an application. In addition to providing data they have access control (read/write) and can tweaked in various other ways based on the application. Some examples include Battery Level (2A19) and Serial Number String (2A25)
SSP (Secure Simple Pairing)
SSP was introduced as a more robust encryption method for Bluetooth in version 2.1. It uses public key cryptography and allows devices to pair in several ways based on input/output capabilities. This included a behind-the-scenes key transfer that only required permission from a user (Just Works SSP). Additionally with smart devices, encrypted connections (bonding) is not required to initiate a connection and transfer data, only if additional security is needed.
Security Manager
The security manager was the other major addition to Bluetooth smart and is incorporated into the Bluetooth stack. This means that all hardware should support the ability to secure connections through bonding and/or transfer data using AES encryption.
Bluetooth Low Energy is becoming widespread in consumer devices and provides a solid framework on which to build connected devices. This post provided a broad overview of bluetooth communication and its more recent support for low cost and low evergy devices. Feel free to check out our case studies for examples of how communication and inteligence was added to products.
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