View
218
Download
0
Category
Preview:
Citation preview
Harmonic Broadcasting for Video-on-Demand Service
Enhanced Harmonic Data Broadcasting And Receiving Scheme
For Popular Video Service
Li-Shen Juhn and Li-Ming Tseng, Department of Computer Science and Information Engineering
National Central University
Introduction
• In conventional broadcasting scheme, each movie is transmitted sequentially on a video channel.– Suppose there is a popular movie which length
is 120 minutes. If we can allocate 4 video channels to broadcast this movie periodically, the viewers waiting time can be reduce to less than 30 minutes.
Introduction
• Harmonic broadcasting is a scheme, which can reduce the access time to 4 minutes as we allocate 4 video channels for a 120-minute movie
Harmonic Broadcasting Scheme
• Parameters:– Movie length --- D (e.g., 120 minutes)
– Consumption rate of the movie --- b (e.g., 10Mbps)
– Size of the movie --- S = D*b
– The movie is equally divide into N segments, and Si is the ith segment of the movie.
– Viewer waiting time --- d• d = D / N
D
Bandwidth = bS1 S2 S3 S4
d
Harmonic Broadcasting Scheme
• Parameters– The ith segment of the movie Si is equally divid
ed into i sub-segment(s) {Si, 1, Si, 2 --- Si, i}
– Let the i sub-segment(s) of Si be put on a logical channel Ci, the bandwidth of Ci is b/i.
Harmonic Broadcasting Scheme
The total bandwidth(B) allocated for the movie is as follows:
Where HN is called the harmonic number of N
d
B = b + b/2 + b/3 + b/4 = 2.083b
HN = 1 + 1/2 + 1/3 + 1/4 = 2.083
Harmonic Broadcasting Scheme
S1
S2, 1
S3, 1
S4, 1
d1
S2, 1
d2
S3, 2
S4, 2
S2, 2
t0
d3
S3, 1
S4, 3
S3, 3S3, 2
S4, 4S4, 1 S4, 2 S4, 3
d4
Waiting Time vs. Bandwidth Allocation
• If we allocate HN = 4 video channels to broadcast a popular movie, we have N = 30. Suppose the length of the movie is 120 minutes. The waiting time will be 120/30 = 4 minutes.
Storage Requirements at Client End
• Suppose the time that we begin to load the S1 from C1 is t0. During t0 + (i - 1)*d to t0 + i * d , the sub-segments(s) that come from Ci+1, …, CN, need to be buffered.
Increased data size
Output data size
buffer size required at t0 + i * d
Introduction of Enhanced Harmonic Data Broadcasting Scheme
• In the previous harmonic broadcasting scheme, however, in some cases, the bandwidth utilization can not achieve 100%– Suppose there are 2 free video channels, the
harmonic scheme can only use about 92% of the bandwidth. ( HN = 2 N = 3 1 + ½ + 1/3 = 1.83, 1.83/2 = 0.92 )
Introduction of Enhanced Harmonic Data Broadcasting Scheme
• For a given bandwidth, the enhanced scheme can improve the bandwidth utilization and reduce further the maximum delay, the average delay of the viewers’ waiting time.
Enhanced Harmonic Broadcasting Scheme
• Parameters– Movie Length --- D (e.g., 120 minutes)– Consumption rate of the movie is b (e.g., 10Mb
ps)– The size of the movie is S = D * b– Suppose the bandwidth that we can allocate for
the movie is B = * b, 1 (e.g., B = 15 Mbp, = 1.5)
Enhanced Harmonic Broadcasting Scheme
• Steps– Step1
• Select an integer f (starting index: enhanced factor) and to find the maximum possible integer e (end index) to let
– Step2• Equally divide the movie into N segments, where
N = e – f + 1
Enhanced Harmonic Broadcasting Scheme
• Step3 – The ith segment Si is equally divide into f +i-1
sub-segment(s) {Si, 1, …Si, f+i-1}. Put the f +i-1 sub-segment(s) of Si on a logical channel Ci. The bandwidth of Ci is b / (f+i-1)
• For a given bandwidth, if we select f = 1, the scheme works exactly the same as the original harmonic broadcasting scheme
Enhanced Harmonic Broadcasting Scheme
The actual bandwidth we allocate for the movie is
d: the consumption time of a data segment
d0
Analysis And Comparison
• Viewer’s waiting time and bandwidth utilization– Before we can start to consume the required movie, we
need to download f – 1 sub-segment(s) of S1. min = (f – 1) * d max = f * d ave = (min + max) / 2
• Uncertainty delay = max - min = d
– For a given bandwidth B, we only allocate B’ to broadcast the movie. The bandwidth utilization is,
Analysis And Comparison – The Effect of the Enhanced Factor : f
• For a given bandwidth, we find that both maximum delay and the delay uncertainty will reduce as we increase the enhanced factor f.
f = 1 (original harmonic broadcasting scheme)
f = 2
Analysis And Comparison – The Effect of the Enhanced Factor : f
• However, increase f can not always reduce the average delay
Original harmonic scheme
= 1.5, f = 1
= 2.0, f = 3
Recommended