Bluetooth : Send AT commends to Headset from Android device

Question

I have established connection between Bluetooh HeadSet and Android phone through HFP profile.

Now I want to send AT commands to HeadSet device.

I have used following components while HFP connection.

IBluetoothHeadset.aidl

BroadcastReciever for ACL

I am not using any createRfcommSocketToServiceRecord socket connection.

and what does following function do ?

boolean sendVendorSpecificResultCode(in BluetoothDevice device,
                                     in String command,
                                     in String arg);