Chapter 10 - The Media Plane

Abstract

This chapter describes the general concepts related to the media plane and examines two concrete examples of protocols used in the media plane for IP multimedia services, real-time transport protocol (RTP) and message session relay protocol (MSRP). The most common media transport protocols used for IP communications are RTP, MSRP, transmission control protocol (TCP), and T.38 fax transmission over UDP. This chapter also defines the concept of the RTP session, which is identified by a transport address and includes just one type of media. RTP typically runs on top of UDP and an RTP packet consists of a header and the payload data, where the payload data contains the actual coded voice or video and the header includes information needed to deliver the services that the protocol provides. RTP was originally conceived to be used in the remit of multicast conferences in the Internet where every participant sends real-time data (e.g., voice) to a multicast address, which is then received by the rest of the participants. The media transport protocol used for transmitting a series of related instant messages is called MSRP, and it represents the media plane component in session-mode messaging communication systems. By using MSRP, the user messages are moved to the media plane by a protocol specifically designed for media transport.