Mixers and Translators

It is not possible to use an RTP mixer to combine encrypted media streams unless the mixer is trusted and has access to the encryption key. This requirement typically prevents mixers from being used if the session needs to be kept confidential.

Translation is also difficult, although not necessarily impossible, if the media streams are encrypted. Translation that involves recoding of the media stream is typically impossible unless the translator is trusted. Some translations, however, do not require recoding of the media stream ”for example, translation between IPv4 and IPv6 transport ”and these may be provided without affecting the encryption, and without having to trust the translator.

Source origin authentication is similarly difficult if the mixer or translator modifies the media stream. Again, if the mixer or translator is trusted, it may re-sign the modified media stream; otherwise the source cannot be authenticated.