White Paper V600

Figure 1 shows the functional components of a PSS client. The functional components can be divided into control, scene description, media codecs and the transport of media and control data. TS 26.233 “Transparent end-to end packet switched streaming service (PSS); General descrip- tion” defines the simple and extended PSS.

The control-related elements are session establish- ment, capability exchange and session control.

•Session establishment refers to methods of invoking a PSS session from a browser or directly by entering an URL in the user interface of the terminal.

•Capability exchange enables choice or adapta- tion of media streams depending on different terminal capabilities.

•Session control deals with the set-up of the individual media streams between a PSS client and one or several PSS servers. It also enables control of the individual media streams by the user. It may involve VCR-like presentation con- trol functions like start, pause, fast forward and stop when presenting media.

The scene description consists of spatial layout and a description of the temporal relation between different media that is included in the media pres- entation. The first gives the layout of different media components on the screen and the latter controls the synchronization of the different media.

The PSS includes media codecs for video, still images, vector graphics, text, audio, and speech.

 

Scene description

 

 

Video

Presentation description

 

 

Still images

Presentation

Audio

Bitmap graphics

description

Speech

Vector graphics

 

 

 

 

 

 

Text

 

 

 

 

 

 

Payload formats

HTTP

RTSP

 

RTP

 

 

 

 

 

 

 

UDP

TCP

 

UDP

 

 

 

 

 

IP

 

 

 

 

 

 

Figure 2. Overview of the protocol stack

Figure 2 describes the media transport protocol stack. Transport of media and control data consists of the encapsulation of the coded media and control data in a transport protocol. This is shown in figure 1 as the “packet based network interface” and displayed in more detail in the protocol stack of figure 2.

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August 2005