Open-Loop Algorithms - Scalable Continuous Media Streaming Systems - page 312

from n 1 channels simultaneously, where n is defined as the order of this scheme (denoted as

GDB n ). Again the maximum start-up latency T is equal to the broadcast duration of the first
media segment L 0 and the client buffer requirement is equal to L 0 ·

−

( f GDB(n) ( N )

b · − 1) [3],

where f GDB(n) ( N ) is the largest media segment size.

18.2.3 Fixed-Segment Variable-Bandwidth Schemes
Alternatively, we can broadcast fixed-size media segments over variable-bandwidth channels.
Notable examples include the Harmonic Broadcasting scheme proposed by Juhn and Tseng
[5] in 1997 and the Poly-harmonic Broadcasting scheme [6] proposed by Paris et al. in 1998.
In the Poly-harmonic Broadcasting scheme, the media stream is partitioned into N equal-
size media segments. Given the desired start-up latency T and a control parameter m , one can
choose N by solving the equation T N . The network bandwidth B is then divided

into N channels (i.e., same as the number of media segments), with the bandwidth for channel
i equal to B i =

= ( m · L ) /

b
m + i ,

1. Media segment L i is then repeatedly broadcast over
channel i . The client, on the other hand, is required to cache media segments from all channels
simultaneously once it enters the system.
The Poly-harmonic Broadcasting scheme can achieve near-optimal performance when m
is large. There are, however, also a few practical issues. First, as the client must receive all
channels simultaneously, the client's access network bandwidth requirement is very large (same
as the server bandwidth requirement). This may not be practical in all wired systems as in some
cases the access bandwidth is substantially more limited than server bandwidth (e.g., ADSL,
cable modem). Second, using a large value of m , while it improves performance, will generate
a huge number of media segments, each requiring its own network channel for transmission.
For some types of network (e.g., IP multicast), this may become a bottleneck as the number
of network channels is limited (e.g., IP multicast addresses). We address these issues in the
Consonant Broadcasting scheme described later in this chapter.

i = 0 , 1 ,..., N −

18.2.4 Variable-Segment Variable-Bandwidth Schemes
The final type of broadcasting scheme is to have both variable segment size and variable channel
bandwidth. Juhn and Tseng proposed the first variable-segment variable-bandwidth scheme
called Staircase Data Broadcasting [4] scheme in 1997. In Staircase Data Broadcasting, a
media stream is first partitioned into N equal-size media segments, based on the number
of channels K , derived from the equation N = K − 1

j = 0 2 j

2 K

1. The network bandwidth
B is then divided equally into K channels, with the same bandwidth b for the i th logical
channel. For eachmedia segment L i ,

= −

it is further divided into 2 i continuousmedia sub-segments

1. Similarly, each logical channel i is further sub-divided into 2 i for i = 0 , 1 ,..., K − sub-

2 i . Finally, each sub-segment is then broadcast repeatedly channels, eachwith a bandwidth of b /

over a separate sub-channel.
The client begins by receiving data from the first occurrence of the beginning of media
segment L 0 at time t 0 . The 2 i continuousmedia sub-segments L i , j ,

2 i

j = 0 , 1 ,..., − 1, within

channel i ( i N . The client access

bandwidth requirement is equal to 2 b , the maximum start-up latency T is equal to the broadcast

= 0 , 1 ,..., N − 1) are then cached at time t 0 + ( L · j ) /