Bluetooth is a widely used wireless communication technology that enables short-range communication between electronic devices. Bluetooth technology is known for its low power usage and relatively low cost, making it a popular choice for various applications across edge computing and IoT deployments. In the last article, we have seen how the transport and session layer played a vital role in making the connection stable and robust. Today we will see how Bluetooth profiles in the application layer support seamless integration of Bluetooth devices across vendors.
Bluetooth Profiles
Bluetooth profiles are additional protocols that build upon the basic Bluetooth standard to more clearly define what kind of data a Bluetooth module is transmitting. While Bluetooth specifications define how the Bluetooth technology works, profiles define how it's used. Bluetooth development teams must ensure that both devices support the required Bluetooth profiles before integration. Not all Bluetooth devices are compatible with all profiles — check the specifications of both devices you want to connect to make sure they both support the required Bluetooth profile. Proper Bluetooth development practice includes referencing the application development guidelines for the profile being implemented. Let us see a few Bluetooth profiles, their features and use cases.
| Profile Name | Features | Applications | Roles |
|---|---|---|---|
| A/V Remote Control Profile(AVRCP) | Remote control of A/V equipment | A/V equipment, in-vehicle equipment, personal computers, mobile phones, and headphones | Controller: Remote control device Target: Device being controlled |
| Advanced Audio Distribution Profile(A2DP) | Streaming music | Headphones, A/V equipment, in-vehicle equipment, personal computers, and mobile phones | Source: Source of the audio Sink: Receiver of the audio |
| Basic Imaging Profile(BIP) | Transmission of basic image data | Printers, digital cameras, personal computers, and mobile phones | Imaging Initiator Imaging Responder |
| Basic Printing Profile(BPP) | Connection between a device (without a printing function) and a printer | Mobile phones, PDAs, and printers | Printer Sender |
| Dial-up Networking Profile(DUN) | Dial-up internet connection via a mobile phone | Mobile phones, personal computers, and PDAs | Gateway Data Terminal |
| File Transfer Profile(FTP) | Data transfer between personal computers | Personal computers and mobile phones | Client Server |
| Hardcopy Cable Replacement Profile(HCRP) | Connection between a device having a printing function and a printer | Printers, Bluetooth adapters for printers, and personal computers | Server Client |
| Hands-Free Profile(HFP) | Hands-Free communication | Mobile phones, headsets, and in-vehicle equipment | Audio Gateway Hands Free Unit |
| Human Interface Device Profile (HID) | Wireless connection of an input device such as a keyboard or mouse | Keyboards, mice, personal computers, and mobile phones | Human Interface Device Host |
| Headset Profile(HSP) | Communication with a headset or headphones | Mobile phones, headsets, in-vehicle equipment, and personal computers | Audio Gateway Headset |
| Object Push Profile(OPP) | Data exchange | Mobile phones, PDAs, personal computers, and in-vehicle equipment | Push Server Push Client |
| Personal Area Network Profile(PAN) | Implementation of a small network | Personal computers, access points, and mobile phones | Network Access Point Service Group Ad-hoc Network Service PAN Service |
| Serial Port Profile(SPP) | Using a Bluetooth device as a virtual serial port | Mobile phones, personal computers, and automotive accessories such as the Bluetooth OBD2 scanner | Device A Device B |
The A2DP HFP Bluetooth profile implementation guide published by Bluetooth SIG provides detailed procedures for combining audio streaming (A2DP) and hands-free calling (HFP) in a single Bluetooth development project. Following this guide ensures correct interoperability across devices from multiple manufacturers.
Multi Profile Specification
One of the salient properties of Bluetooth technology is the Multi Profile specification (MPS). Many applications can run in parallel without impacting each other (i.e. 2 or more Bluetooth profiles can run in parallel). MPS does not have any separate profile — it integrates existing profiles. There are 4 configurations applicable in MPS.
| Single Profile Single Device(SPSD) | Single profile is used between a single pair of Bluetooth devices. No other profile is used concurrently. |  |
| Single Profile Multiple Devices(SPMD) | Single profile is used concurrently between several Bluetooth devices. For example, one device runs multiple instances of the same Bluetooth profile, and each instance is connected to a separate Bluetooth device supporting that profile. |  |
| Multiple Profiles Single Device(MPSD) | Multiple Bluetooth profiles are used concurrently between two devices. |  |
| Multiple Profiles Multiple Devices(MPMD) | Multiple Bluetooth profiles are used concurrently among several devices. The number of devices is defined case by case. This is the most complex Bluetooth development scenario. |  |
Let's see a use case for Multi profile and single device scenario and what inter-profile control takes place to deliver a smooth user experience.
Answer Incoming Call during Audio Streaming (MPSD)
In this scenario the smartphone suspends the audio stream when the incoming call is answered. An ongoing HFP Service Level Connection between the devices exists and it will become active. This illustrates how Bluetooth technology coordinates multiple Bluetooth profiles simultaneously.
Data & Control Sequence:
MPSD Use case
Similarly for other use cases the following profile combinations work.
| Use case | Profile Combination |
|---|---|
| Outgoing call during audio streaming | AVRCP, A2DP & HFP |
| Reject/Ignore Call during audio streaming | AVRCP, A2DP & HFP |
| HFP Call termination during AVP connection | AVRCP, A2DP & HFP |
| Play Audio during active call | AVRCP, A2DP & HFP |
Conclusion
The flexibilities offered by Bluetooth technology have empowered its widespread adoption across diverse domains. Understanding the different types of Bluetooth profiles and how they are used helps device designers and Bluetooth development teams set things up correctly. This ensures everything works smoothly together across vendors. Testers also benefit from knowing these Bluetooth profiles well, as they can validate multi-profile scenarios using Bluetooth SIG testing tools. In the next section, we'll look at how Bluetooth technology handles connections with multiple devices simultaneously.