Which of the following trunks can be used to allow Cisco TelePresence VCS and Cisco Unified CM to securely
internetwork with each other?

A.
only SIP trunks

B.
only H.323 trunks

C.
both SIP and H.323 trunks

D.
neither SIP nor H.323 trunks

Explanation:
Only Session Initiation Protocol (SIP) trunks can be used to allow Cisco TelePresence Video
Communication Server (VCS) and Cisco Unified Communications Manager (CM) to securely internetwork with
each other. Security is provided by using Transport Layer Security (TLS) for signaling, and the Unified CM
server must trust the VCS certificate. If a common certificate authority (CA) is used for both devices, the trust
process is simplified.
Unified CM can use H.235 to provide security for H.323, and Unified CM can use Secure Real-time Transport
Protocol (SRTP) to encrypt SIP streams. However, H.235 and SRTP cannot be internetworked on Unified CM.

Cisco: Cisco Collaboration Security: Cisco TelePresence Video Communication Server (VCS)