A backend CTI application that communicates with the phone using the UserData tunnel cannot retrieve information on device capabilities such as XSI feature support on a phone. Due to this lack of information, and to ensure compatibility, only a minimum set of features were generally configured.
The Device Capability Query via CTI feature overcomes this limitation. This feature allows a CTI-based application or a Cisco Unified Communications Manager application to query a registered phone for device capabilities using the UserData tunnel interface of the phone (over SCCP or SIP and RemoteCC).
Applications that have an HTTP interface with a phone do not have this limitation. The HTTP request from such phones include XSI capabilities header, and the DeviceInformationX servlet of such phones can be accessed to retrieve other device information.
Although designed to work using CTI over the UserData tunnel, this feature can also work over HTTP using the POST method.