Which of the following protocols describes the operation of security In H.323?

H.239 defines dual video stream capability in H.323 for content sharing applications and has no role in authentication or encryption.

H.245 is the H.323 control protocol used for capability negotiation and logical channel signaling between endpoints, not for security or encryption.

H.235 is the ITU-T recommendation that provides authentication, integrity, and confidentiality services for H.323 voice and video communication. It defines how security tokens, certificates, and cryptographic mechanisms are applied to both H.323 call signaling and media streams to protect communications end to end.

H.225 handles call signaling and RAS (Registration, Admission, and Status) messaging in H.323 but does not define security or cryptographic protections.