3. SRTP Framework

3. SRTP Framework

RTP is the Real-time Transport Protocol [RFC3550]. We define SRTP as a profile of RTP. This profile is an extension to the RTP Audio/Video Profile [RFC3551]. Except where explicitly noted, all aspects of that profile apply, with the addition of the SRTP security features. Conceptually, we consider SRTP to be a "bump in the stack" implementation which resides between the RTP application and the transport layer. SRTP intercepts RTP packets and then forwards an equivalent SRTP packet on the sending side, and intercepts SRTP packets and passes an equivalent RTP packet up the stack on the receiving side.

Secure RTCP (SRTCP) provides the same security services to RTCP as SRTP does to RTP. SRTCP message authentication is MANDATORY and thereby protects the RTCP fields to keep track of membership, provide feedback to RTP senders, or maintain packet sequence counters. SRTCP is described in Section 3.4.