When a device sends an inquiry response, it includes a bitmask which contains its class of device, such as "Phone", "Computer" etc. These bitmasks are used to filter out irrelevant devices, for instance, when trying to connect to an audio device, the entries which do not contain the "headset" bits set can be ignored. The class of device is also usually used to show a icons in device discovery UIs.
The class of device/service field is divided into three parts: the service class, the major device class and the minor device class.
Service Class
The service class bits contain information about what the device can do, regardless of what type of device it is. For example, a computer can provide several services, such as networking, audio, object transfers and so on.
The service bits currently defined are these:
- Positioning
- Networking
- Rendering
- Capturing
- Object transfer
- Audio
- Telephony
- Information
There is also one special "service" bit which is used to tag a device during a Limited Discoverable Mode? search.
Major Device Class
Currently there are 10 major device classes defined in the Baseband Assigned Numbers:
- Miscellaneous
- Computer
- Phone
- LAN /Network Access point
- Audio/Video
- Peripheral
- Imaging
- Wearable
- Toy
- Uncategorized
Minor Device Class
The minor device class bits contain more specific information about the device and depend on the values assigned in the Major Device Class bits.
For example, if the major device class bits are set to "Computer", the minor device class bits can specify the device as being one of the following types of computers:
- Uncategorized
- Desktop workstation
- Server-class computer
- Laptop
- Handheld PC/PDA
- Palm sized PC/PDA
- Wearable computer
More details can be found at the Bluetooth SIG's assigned numbers page.
