Which lists features that are supported by Cisco Unified Border Element?

Cisco 'x-cisco-tip' SIP headers are proprietary headers specific to Cisco TelePresence Interoperability Protocol and are not a feature set associated with CUBE.

iSAC (Internet Speech Audio Codec) is a wideband VoIP codec developed by GIPS/Google, and CUBE does not support a low-complexity variant of this codec.

CUBE explicitly supports Cisco Customer Voice Portal (CVP) survivability using TCL-based scripts that handle inbound calls locally when the CVP server is unreachable. This feature can be configured with high availability to ensure continued operation, and it is a documented CUBE capability for enterprise contact center deployments.

Colocation of VRF (Virtual Routing and Forwarding) instances with Cisco Unified Communications is not a supported CUBE feature; CUBE has specific and limited VRF-aware capabilities that do not include VRF colocation.