Biometric Unit Life Cycle
Every biometric unit goes through various stages. It is created, configured, and eventually deleted.
Creation
When the Windows Biometric Service starts or when it receives a hardware notification from the Plug and Play manager, it scans for any hardware that supports the well-known interface GUID_DEVINTERFACE_BIOMETRIC_READER (E2B5183A-99EA-4cc3-AD6B-80CA8D715B80). For each biometric device discovered it then:
- Opens a handle to the device.
- Queries the device capabilities by using a Windows Biometric Driver control interface.
- Opens the device registry key and attempts to locate information about any associated adapter plug-ins.
- Opens the Windows Biometric Service registry key and searches for information about any global plug-ins that should override the device specific values found in the preceding step.
- Builds a biometric unit to represent the device and passes the unit to a biometric service provider.
Configuration
After a biometric service provider (BSP) accepts a biometric unit, it configures the unit and assigns it to a sensor pool. For more information, see Sensor Pools. The unit is configured by loading the appropriate adapters, connecting to a template store, and possibly changing the operating mode. A biometric unit can be configured to operate in one of two modes:
- In the basic mode, the unit acts as a simple capture device. It does not use onboard processing or storage but relies entirely on software adapters for additional support. It should be able to generate samples in a standard format. For example, fingerprint readers should generate samples that comply with ANSI INCITS 381-2004. The purpose of the basic mode is to support interoperability among components from different vendors.
- In the advanced mode, the biometric unit uses onboard processing and storage functions. It must expose the standard interfaces but can generate and process samples in any format desired.
When a biometric unit is moved from one sensor pool to another, its adapters are unloaded and it is reconfigured for the new sensor pool. The identity of the biometric unit remains constant; only the hardware configuration and adapter plug-ins change.
Shut Down
When the Windows Biometric Service shuts down or when the Plug and Play manager notifies it that a unit has been removed, the service deletes all biometric units.