Inc. The primary output of the AVT working group is the Real-time Transport Protocol. These topics will be discussed further in Internet-Drafts and on the mailing list. In addition to RFC1889 and 1890, there are four drafts awaiting publication which define the RTP payload formats for H.261, JPEG, MPEG and CellB video encodings. At this meeting, three new payload formats were proposed. In addition, to accommodate hierarchical encodings, changes to some rules stated in the main RTP spec were also proposed.
Hierarchical encodings break the media stream into an ordered collection of layers.
The base layer provides a complete but low-quality signal that may be enhanced by composing it with additional layers. Receivers adjust the number of layers received to avoid exceeding the network bandwidth available or the receiver's own processing power. The layers are sent on separate IP multicast addresses so that multicast routing can prune the distribution tree separately for each layer. For unicast, the single address would be used for all layers. This convention does not impact the specification of RTP itself.