Ericsson Ericsson RTP has always been a protocol that supports multiple participants each sending their own media streams in an RTP session. Unfortunately many implementations aimed only at point to point voice over IP with a single source in each end-point. Even client implementations aimed at video conferences have often been built with the assumption around central mixers that only deliver a single media stream per media type. Thus any application that wants to allow for more advance usage where multiple media streams are sent and received by an end-point has a problem with legacy. This issue is analyzed, and RTP clarifications and signalling extensions are proposed to handle this issue. A related issue is how to perform simulcast, in the meaning of sending multiple encodings or representations of the same media source, when using RTP for media transport. This is further analyzed and possible solutions discussed and we arrive at a conclusion for session multiplexing of simulcast versions. We also found a number of related issues when having multiple streams and simulcast.