In the Cisco Unified Customer Voice Portal 4.0.x Comprehensive model using SIP, a call arrives, a user is prompted to enter an account number and is transferred to a Cisco Unified Contact Center Enterprise agent. Which of the following is not a role performed by the Cisco Voice Gateways involved in this call flow?

A.
recognizing DTMF digits, converting them to RFC 2833 RTP, and sending them to the Cisco Unified Customer Voice Portal Call Server

B.
converting TDM speech to IP

C.
generating ring tone to the caller from a ring tone audio file stored in flash memory on the Cisco Voice Gateway

D.
retrieving VXML documents and audio files and rendering them to the caller