Headset Profile (Windows CE 5.0)

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The Bluetooth Headset Profile (HSP) depends on the Serial Port Profile (SPP), and defines procedures to support interoperability between a headset and a mobile device. The mobile device is the audio gateway (AG) that provides both input and output audio to the headset. The headset acts as an audio input and output mechanism for the AG, and controls the mobile device through AT commands.

Microsoft® Windows® CE supports HSP by providing the Audio Gateway Service that links Bluetooth devices by using the Winsock interface to the Bluetooth Protocol Architecture. This service also interfaces with the TAPI to control a cellular phone.

The headset sends AT commands to the AG, in response to user-initiated events. The following table shows the AT commands supported in Windows CE.

AT command Description
AT+CKPD=200 Notifies the AG service when a button on the headset is pressed.
AT+VGM=<gain> Notifies the AG service when the microphone volume on the headset is changed to the specified gain value.
AT+VGS=<gain> Notifies the AG service when the speaker volume on the headset is changed to the specified gain value.

When the AG receives an AT command, it processes the command and controls the headset by returning an unsolicited result code. The following table shows the result codes supported in Windows CE.

Result code Description
+VGM=<gain> Sets the microphone volume on the headset.
+VGS=<gain> Sets the speaker volume on the headset.
RING Rings the headset.

The procedures specified by the HSP define the set of features that the headset supports. The following table shows the features supported by Microsoft® Windows® CE.

Feature Procedure
Incoming audio connection The AG service starts an incoming audio connection session and sends the RING result code to the headset. This result code alerts the user, who then accepts the connection. In response to the user-initiated event, the headset sends the AT+CKPD command to the AG service.
Outgoing audio connection The headset starts an outgoing audio connection by sending the AT+CKPD command to the AG service, which further establishes the connection and routes the audio to the headset.
Audio connection transfer The headset initiates an audio connection transfer from the AG to the headset by sending the AT+CKPD command. User-initiated audio connection transfers from the headset to the AG are performed on the AG.
Remote audio volume control To set the volume of the microphone or of the speaker on the headset, there must be an active connection between the AG and the headset.

To change the microphone or speaker volume, the AG sends the +VGM or +VGS result code, respectively, to the headset and specifies the gain as a parameter of the result code.

The following list shows the user interface requirements for the headset profile to work:

  • The user interface must toggle audio output between the headset and the mobile device.
  • The user interface must allow the user to choose between the headset and the phone to receive or place a call.

For more information about the procedures related to these features, see the Headset Profile Specification at the Official Bluetooth Wireless Info Web site.

See Also

Bluetooth OS Design Development | Bluetooth Profiles | Audio Gateway Service

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