Introduction - Scalable Continuous Media Streaming Systems - page 4

NIC NIC

Buffer Network Buffer

Decoder Display

Media
Data

Media Server Media Client

Media Server:
• Media Data
• Storage subsystem
• Buffers
• Network
• Processor

Media Client :
• Media Data
• Media Codec
• Buffers
• Network
• Processor

Figure 1.1 Basic building blocks of a multimedia system

media data are first buffered in main memory and/or disk storage, and then eventually decoded
and presented to the end user.
A unique characteristic of this system model is that the system components involved work
in tandem in the data delivery process. Thus, a problem in any one of the system components
can degrade the performance of the whole chain. In the following text we will investigate these
system components and their interactions in more detail.

1.2 Media Data
The 'multi' in multimedia refers to multiple media of same or different types that are authored,
delivered, and presented together. There are clearly many different types of media, from the
simplest plain text, to formatted text, graphics, images, audio, video, or even tactile information.
We can broadly classify these diverse types of media into two main categories, especially in
the context of multimedia data delivery.
The first type - discrete media - refers to media data that have no explicit requirement for
presentation timings. For example, consider retrieving an image from a web server for display
in a web browser. Depending on the network bandwidth availability, the browser may take
a variable length of time to receive the image data before they can be decoded for display.
This may take, for example, from fractions of a second up to tens of seconds or even longer,
depending on the size of the image and the network bandwidth available. Obviously, it is
desirable to reduce this delay to as short a time as possible but as long as the image data are
all correctly received, rendered, and displayed, the request is considered to be successfully
completed. In other words, there is no restriction inherent in the media data that requires the
media data to be presented at a certain time or within a certain delay limit. This is also why
the network traffic resulting from delivering discrete media is also known as elastic traffic to
reflect the media's ability to tolerate variations in delivery time.