Introduction - Scalable Continuous Media Streaming Systems - page 8

Send data

Server

. . .

Client

Send req

Present data

Delay

=

Delay Data Size/Transmission Rate

Figure 1.5 The start-up delay in the download data delivery model

Send lots of data

Server

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Client

Send req

Playback movie

A long delay

= = × =

Delay Data Size /TransmissionRate 5.4GB 8/8Mbps 1.5 hours

Figure 1.6 Calculating the delay for downloading a 5.4GB video for playback

can also be decoded and played back. For example, video data are composed of video
frames, which can be played back once all the data of a frame have been received by the
client.
Taking advantage of this property of continuous media, we can then modify the download
model into a streaming model where data are being played back while data reception is in
progress, as depicted in Figure 1.7. Specifically, after sending a request to the server to begin the
streaming process, the client will wait for the first parcel of data to arrive and then begin
playback while receiving the second parcel of data, and so on. Thus, the data transfer and
the playback processes are pipelined, therefore significantly shortening the delay to begin
media playback.