Information Technology Reference
In-Depth Information
6
Media Data Streaming
In the previous chapters the focus was on retrieving media data from the disk storage to
the main memory for transmission to the client. In this chapter we follow the data flow to
investigate issues in streaming the media data over the network to the client hosts. We can
separate themedia streaming problem into two aspects: protocol and scheduling. The former
covers the issues in the design of the transport/application layer protocols between themedia
server and the media client. Some key issues include resource identification, playback
controls, media data synchronization, authentication, and digital rights management, etc.
The latter covers the data transmission issues such as scheduling media data transmission
to sustain continuous media playback, transmission of variable-bit-rate media streams, and
adaptation of the media stream to changing network conditions.
This chapter addresses the protocol issues, discusses the feasibility of streaming media
data using the existing Internet transport protocols (TCP/UDP), and gives a brief overviewof
the recently standardized Internet streaming protocols RTSP, RTP, and RTCP. The schedul-
ing issues will be addressed in Chapters 7 and 8.
6.1 Streaming over TCP/UDP
Before discussing the specialized streaming protocols, let us first investigate the feasibility of
using the existing Internet protocols for streaming applications. If we consider the transport
layer protocols, then the Internet already supports the Transmission Control Protocol (TCP) [1]
and the User Datagram Protocol (UDP) [2]. TCP is the transport protocol used by most of the
Internet applications, including the WWW, FTP, telnet, and so on. It is a connection-oriented
protocol that has built-in error control, flow control, and congestion control [3, 4]. In other
words, TCP shields the application from much of the complexities in managing traffic flowing
through the Internet. This greatly simplifies application development and TCP also possesses
a desirable property - it shares network resources with other competing traffic flows in a fair
manner [5]. So, given the many desirable features of TCP, the natural question is, can we
simply stream media data over TCP as depicted in Figure 6.1?
The answer depends on the bandwidth requirement, network characteristics, and the desired
quality of service. For example, if network bandwidth is abundant compared to the media data
Search WWH ::




Custom Search