This memo describes extensions for the RTP payload format defined in RFC 3640 for the transport of MPEG Surround multi-channel audio. Additional Media Type parameters are defined to signal backwards- compatible transmission inside an MPEG-4 Audio elementary stream. In addition, a layered transmission scheme that doesn't use the MPEG-4 systems framework is presented to transport an MPEG Surround elementary stream via RTP in parallel with an RTP stream containing the downmixed audio data. [STANDARDS-TRACK]