What is the capability of SRTP in the context of SIP?

SRTP, or Secure Real-time Transport Protocol, is specifically designed to provide encryption, message authentication, and integrity, and replay protection to RTP (Real-time Transport Protocol) data streams, which are frequently used for transmitting audio and video in VoIP (Voice over Internet Protocol) communications. In the context of SIP (Session Initiation Protocol), SRTP plays a crucial role in securing the media streams that are established for a call.

When a SIP session is initiated, it can set up the transmission of audio and video data via RTP. SRTP ensures that these media streams are encrypted and thus protects the content being transmitted from eavesdropping or tampering. While SIP itself is responsible for signaling—establishing, modifying, and terminating communication sessions—it does not inherently secure the media that flows through those sessions.

Though SIP can use protocols like TLS (Transport Layer Security) to secure the signaling, SRTP specifically addresses the need for media security. Thus, the capability of SRTP involves securing the actual media streams associated with SIP sessions, making this answer accurate. Other selections fail to recognize SRTP's primary function regarding media security or mischaracterize its relationship to SIP.