5.2 Multicast Streams

If a session description contains a multicast media stream which is listed as receive (send) only, it means that the participants, including the offerer and answerer, can only receive (send) on that stream. This differs from the unicast view, where the directionality refers to the flow of media between offerer and answerer.

Beyond that clarification, the semantics of an offered multicast stream are exactly as described in RFC 2327 [1].