Kimon wants to ensure that his VoIP session initialization is secure. What protocol should he ensure is enabled and required?

SIPS, the secure version of the Session Initiation Protocol (SIP) for VoIP, adds TLS encryption to keep the session initialization process secure. SVOIP and PBSX are not real protocols, and SRTP is the secure version of RTP, which secures the media stream rather than the signaling.