Codec Freedom -- Specifications -- Supporting ZRTP
ZRTP enables end-to-end encryption of media flows in the absense of infrastructure. It travels over the same UDP packet flow as the media stream, but is clearly distinguishable from it.
In spite of being carried over RTP, ZRTP is not a realtime protocol. That means that there is no need to insert ZRTP into the codec flow that travels with the highest priority; instead, the plain message flow carried over AMQP can be used.
This specification defines a MIME-type
message/x-zrtp to hold the ZRTP
message content, so that we can indeed carry them over as an AMQP message. The
contents of this package match [Figure 2 in RFC 6189].
When an application with ZRTP forwarding support receives this message, it relays the message over the RTP channel, using its format that is incompatible with plain RTP media traffic.