Proxy caching for efficient video services over the Internet

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Transcript of Proxy caching for efficient video services over the Internet

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0 10 20 30 40 50 60 70 80 90 10041.5

42

42.5

43

43.5

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Max buffer size

Same as in (a)All lifted

(a): No Caching

10

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0 200 400 600 800 1000 1200 1400 1600 1800 20000

10

20

30

40

50

Number of frames in decoder buffer during playback

Num

ber

of fr

ames

in b

uffe

r, B

(t)

Time

Number of frames = 2000, Avg. data rate = 2.498 Mbps, Prefeteched frames=2, Lower client buf. bound = 0 Kbits, Desired channel rate = 2.500 Mbps,

0 200 400 600 800 1000 1200 1400 1600 1800 20000

100

200

300

400

500

600

Number of bits in decoder buffer

Num

ber

of K

bits

in b

uffe

r

Time

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Number of frames in user buffer

Bhigh

Very few frames in the buffer,easy to underflow if congestionoccurs at that time

3t2t 2t ’ 3t t 4 t 5 t 5t 1 ’ ’ 3t2t 2t ’ 3t t 4 t 5 t 5t 1 ’ ’

Sadd

Sadd

SaddBhigh +

BhighWith Max buffer limit =

U2 U2

The lower buffer bound increases as initial buffering increases, initial

Required

Max buffer size

bufferingAddtional

(a): Required initial buffering only (b): With additional buffering

buffering

Time Time

B (t)

Sreq

+Sreq

Max buffer size

U1

0

B (t)1

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AdditionalCache Segment

RequiredCacheSegment

RequiredCacheSegment

Intermediated framesto be cached

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First frame

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Frames

(b) Selective caching: cache required segment and intermdieate frames

Sreqs

add Sreq

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First frame

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Frames

(a) Initial caching: cache required segment and additional segment

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Number of frames in user buffer

Number of frames in user buffer

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Receving cached frames from proxy

Without caching frames at t4

U1initial Required

Max buffer size

(a): Required initial buffering only

buffering

Time

Max buffer size

(b): Selected caching on proxy

B (t)

Time

Sreq

Sreq

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0 10 20 30 40 50 60 700

0.05

0.1

0.15

0.2

0.25

Number of frames = 2000, Avg. data rate = 2.498 Mbps, Prefeteched frames = 2, Lower client buf. bound = 0 Kbits, Constant channel rate = 2.500 MbpsChannel Error Probability = 0.20

The probability of frame to be lost/delay v.s. buffer contents

Number of previous frames in decoder buffer when transmitting the current frame

Lost

pro

babi

lity

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0 200 400 600 800 1000 1200 1400 1600 1800 20000

20

40

60

80

Number of frames in decoder buffer

Total Number of frames = 2000; Avg. video data rate = 2.498 Mbps, 13.02 Kbits/frame;Prefeteched frames = 2; Channel rate = 2.500 Mbps;, Cache Space on proxy = 3000Kbits

B(t

) in

num

ber

of fr

ames

Time

Cached frames is indicated by "*"Number of frames cached = 211

************************* ***************************************************************************************************** ************************* **************************************************************

0 200 400 600 800 1000 1200 1400 1600 1800 20000

200

400

600

800 Number of bits(KB) in decoder buffer

B(t

) in

Kbi

ts

Time

Cached frames is indicated by "*"Number of frames cached = 211

************************* ***************************************************************************************************** ************************* **************************************************************

After selective cachingBefore selective caching

After selective cachingBefore selective caching

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