1 Video Delivery Techniques. 2 Server Channels Videos are delivered to clients as a continuous...

1

Video Delivery Techniques

2

Server Channels• Videos are delivered to clients as a

continuous stream.

• Server bandwidth determines the number of video streams can be supported simultaneously.

• Server bandwidth can be organized and managed as a collection of logical channels.

• These channels can be scheduled to deliver various videos.

3

Using Dedicated Channel

Video Server

Client

Too Expensive !

Client

Client

Client

Dedicated stream

4

“Video on Demand” Quiz

1. Video-on-demand technology has many applications:

Electronic commerce Digital libraries Distance learning

News on demand Entertainment All of these applications

2. Broadcast can be used to substantially reduce the demand on server bandwidth ? True False

3. Broadcast cannot deliver videos on demand ? True False

? ?

5

Push Technologies

Broadcast technologies can deliver videos on demand.

Requirement on server bandwidth is independent of the number of users the system is designed to support.

If your answer to Question 3 was “True”, you are wrong:

Less expensive & more scalable !!

6

Simple Periodic BroadcastStaggered Broadcast Protocol

• A new stream is started every interval for each video.

• The worst service latency is the broadcast period.

Time

W

Channel 1

Channel 4

L

video i

video i

video i

video i

video i

video i

video i

video i

video j video jChannel 5

video jvideo j

video jvideo jChannel 7

W=L/N where N is thenumber of channelsW=L/4

7

Simple Periodic Broadcast

• A new stream is started every interval for each video.

• The worst service latency is the broadcast interval.

Advantage: The bandwidth requirement is proportional to the number of videos (not the number of users.)

Can we do better ?

8

Limitation of Simple Periodic Broadcast

• Access latency can be improved only linearly with increases to the server bandwidth.

• Substantial improvement can be achieved if we allow the client to preload data

9

Pyramid Broadcasting – Segmentation

[Viswanathan95]

• Each data segment Di is made times the size of Di-1 , for all i.

= , where B is the system bandwidth; M is the number of videos; and K is the number of server channels. opt = 2.72 (Euler’s constant).

1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 Channel 1

1 2 3 4 1 2 3 4 1 2 3 4 1 2

1 2 3 4 1 2 3

1 2 3

Channel 2

Channel 3

Channel 4

timebroadcastinterval ofchannel 1

Siz

es

incr

ea

se g

eo

me

tric

ally

The same video fragment of video 1

broadcast interval of channel 2

broadcast interval of channel 3

KM

B

10

Pyramid Broadcasting Download & Playback

Strategy• Server bandwidth is evenly divided

among the channels, each much faster than the playback rate.

• Client software has two loaders:

– Begin downloading the first data segment at the first occurrence, and start consuming it concurrently.

– Download the next data segment at the earliest possible time after beginning to consume the current data segment.

11

Disadvantages of Pyramid Broadcasting

• The channel bandwidth is substantially larger than the playback rate

• Huge storage space is required to buffer the preloaded data

• It requires substantial client bandwidth

Client bandwidth is typically the most expensive component of a VOD system

12

Permutation-Based Pyramid Broadcasting (PPB) [Aggarwal96]

• PPB further partitions each logical channel in PB scheme into P subchannels.

• A replica of each video fragment is broadcast on P different subchannels with a uniform phase delay.

Cha

nnel

Ci

Video V1

Video V2

A subchannel

Pause to allow the playback to catch up

Begin downloading Resume downloading

13

Advantages and Disadvantages of PPB

• Requirement on client bandwidth is substantially less than in PB

• Storage requirement is also reduced significantly (about 50% of the video size)

• The synchronization is difficult to implement since the client needs to tune to an appropriate point within a broadcast

14

• Each video is fragmented into K segments, each repeatedly broadcast on a dedicated channel at the playback rate.

• The sizes of the K segments have the following pattern:

[1, 2, 2, 5, 5, 12, 12, 25, 25, …, W, W, …, W]

Skyscraper Broadcasting [Hua97]

Size of larger segments are constrainedto W (width of the “skyscraper”).

Even group Odd group

wLatencyService

segment#length video

15

Generating Function

The broadcast series is generated using the following recursive function:

1 If n = 1,

2 If n = 2 or 3,

2 · f(n - 1)+1 If n mod 4 = 0.

f(n-1) If n mod 4 = 1,

2 · f(n - 1) + 2 If n mod 4 = 2,

f(n – 1) If n mod 4 = 3

f(n) =

16

• The Odd Loader and the Even Loader download the odd groups and the even groups, respectively.

• The W-segments are downloaded sequentially using only one loader.

• As the loaders fill the buffer, the Video Player consumes the data in the buffer.

Skyscraper Broadcasting Playback Procedure

17

Advantages of Skyscraper

Broadcasting• Since the first segment is very

short, service latency is excellent.

• Since the W-segments are downloaded sequentially, buffer requirement is minimal.

Pyramid Skyscraper

18

SB Example

Blue people share 2nd and 3rd fragments and 6th, 7th, 8th with Red people.

1

2

3

4

5

6

7

8

19

6

2

3

time

5

7

...

4

2 3 4 5 6 7 16. . .

Channel 1

Channel 2

Channel 3

Channel 4

Channel 5

Channel 6

Channel 7

Channel 15

Channel 16

Playback Schedule:

Loader 1

Loader 1

Loader 1

Loader 1

Loader 1

Loader 1

Loader 2

Loader 2

Loader 2

BufferLoader 1

Loader 2

VideoPlayer

BroadcastChannels

An

oth

er

Ap

pro

ach

20

CCA Broadcasting• Server broadcasts each

segment at the playback rate

• Clients use c loaders

• Each loader download its streams sequentially, e.g., i th loader is responsible for segments i, i+c, i+2c, i+3c, …

• Only one loader is used to download all the equal-size W-segments sequentially

W

Channel 1

Channel 2

Channel 3

Channel 4

Channel 5

Channel K

Group 1

Group 2

Group i

C = 3 (Clients have three loaders)

.1)(mod)1(

,1)(mod)1(2

,11

)(

cnnf

cnnf

n

nf

21

Advantages of CCA

• It has the advantages of Skyscraper Broadcasting.

• It can leverage client bandwidth to improve performance.

22

Cautious Harmonic Broadcasting

(Segmentation Design)• A video is partitioned into n equally-sized

segments.

• The first channel repeatedly broadcasts the first segment S1 at the playback rate.

• The second channel alternately broadcasts S2 and S3 repeadtedly at the playback rate.

• Each of the remaining segment Si is repeatedly broadcast on its dedicated channel at 1/(i–1) the playback rate.

23


(Playback Strategy)

• The client can start the playback as soon as it can download the first segment.

• Once the client starts receiving the first segment, the client will also start receiving every other segment.

24


Advantage: Better than SB in terms of service latency.

Disadvantage: Requires about three times more receiving bandwidth compared to SB.

Implementation Problem:

• The client must receive data from many channels simultaneously (e.g., 240 channels are required for a 2-hour video if the desired latency is 30 seconds).

• No practical storage subsystem can move their read heads fast enough to multiplex among so many concurrent streams.

25

Pagoda BroadcastingDownload and Playback

Strategy

• Each channel broadcasts data at the playback rate

• The client receives data from all channels simultaneously.

• It starts the playback as soon as it can download the first segment.

26

Pagoda BroadcastingAdvantage & Disadvantage

Advantage: Required server bandwidth is low compared to Skyscraper Broadcasting

Disadvantage: Required client bandwidth is many times higher than Skyscraper Broadcasting

Achieving a maximum delay of 138 seconds for a 2-hour video requires each client to have a bandwidth five times the playback rate, e.g., approximately 20 Mbps for MPEG-2

System cost is significantly more expensive

27

New Pagoda Broadcasting [Paris99]

• New Pagoda Broadcasting improves on the original Pagoda Broadcasting.

• Required client bandwidth remains very high

Example: Achieving a maximum delay of 110 seconds for a 2-hour video requires each client to have a bandwidth five times the playback rate.

Approximately 20 Mbps for MPEG-2

System cost is very expensive

28

Limitations of Periodic Broadcast

• Periodic broadcast is only good for very popular videos

• It is not suitable for a changing workload

• It can only offer near-on-demand services

29

Batching• FCFS

• MQL (Maximum Queue Length First)

• MFQ (Maximum Factored Queue Length

ResourcesWaiting queue for video i

newrequest

longest queue length

ResourcesWaiting queue for video i

newrequest

lf

l

ln

n

1

1

fis the largest

1Access frequency

of video 1

777 ResourcesWaiting queue

newrequest

Still only near VoD !

Can multicast provide true VoD ?

30

Current Hybrid Approaches

• FCFS-n : First Come First Served for unpopular video and n channels are reserved for popular video.

• MQL-n : Maximum Queue Length policy for unpopular video and n channels are reserved for popular video.

• Performance is limited.

31

New Hybrid Approach

SkyscraperBroadcasting scheme (SB)

Largest Aggregated Waiting TimeFirst (LAW)

Periodic Broadcast Scheduled Multicast

+

32

LAW(Largest Aggregated Waiting Time First)

• MFQ tends to MQL; loosing fairness

q1 / f1, q2 / f2, q3 / f3, q4 / f4, …

f1 f2 f3 f4 ...

q1, q2, q3, q4, ...• Whenever a stream becomes available, schedule the

video with the maximum value of Si :

Si = c * m - (ai1+ ai2 + …+ aim ),where c is current time,

m is total number of requests for video i,

aij is arrival time of jth request for video i.(Sum of each request’s waiting time in the queue)

33

LAW (Example)

• By MFQ, q1*t1= 5*(128-106)=110,

q2*t2 = 4*(128-100)=112. selected By MFQ

• Average waiting times are 12 and 8 time units.

• S1 = 128*5 - (107+111+115+121+126) = 60 selected

S2 = 128*4 - (112+119+122+127) = 32 by LAW

Request for video no.1

106 107 111 115 121 126 128

Time

last multicast

Request for video no.2

100 112 119 122 127 128

Time

last multicast

Current

Current

R11 R12 R13 R14 R15

R21 R22 R23 R24

34

AHA (Adaptive Hybrid Approach)• Popularity is re-evaluated periodically.• If a video is popular so broadcasting by SB currently,

then go Case.1. Otherwise, go Case.2.

Video is popular

Video ispopular ?

Terminate the SB broadcast after all the dependent playbacks end

Mark the waiting

queue as anLAW queue

Return the channels to the channel pool

YesNo

K channelsavailable ?

Initiate the SB

broadcast

Yes

No

Case.1

Case.2

Video is popular

Video ispopular ?

No

YesMark the waiting

queue as anLAW queue

The video is assumed torequire K logical channels

35

Performance Model • 100 videos (120 min. each),• Client Behavior follows

- the Zipf distribution (z = 0.1 ~ 0.9) for choice of videos,- the Poisson distribution for arrival time.- popularity is changing gradually every 5 min for dynamic environment.- for waiting time, = 5 min., s = 1 min.

• Performance Metrics- Defection Rate,- Average access latency,- Fairness, and- Throughput.

36

LAW vs. MFQ

Varying Request rate

0

1

2

3

4

5

6

7

8

5 7.5 10 12.5 15 20 30

Request Arrival rate (requests/min.)

Un

fair

nes

s

MFQLAW

Varying Server Capacity

0

1

2

3

4

5

6

7

8

300 400 500 600 700 800 900

Server Capacity (channels)

Un

fair

nes

s

MFQLAW

Varying Skew Factor

0

1

2

3

4

5

6

7

8

0.1 0.2 0.3 0.4 0.5

Skew Factor (Z)

Un

fair

nes

s

MFQLAW

37

AHA vs. MFQ-SB-nAverage Latency

00.5

11.5

22.5

33.5

44.5

5

600 800 1000 1200 1400 1600 1800


Av

era

ge

La

ten

cy (

min

.)

MFQ-SB-nAHA

Throughput

0

5

10

15

20

25

30

35

40

45

600 800 1000 1200 1400 1600 1800


Th

rou

gh

pu

t

MFQ-SB-nAHA

Defection Rate

0

10

20

30

40

50

60

70

600 800 1000 1200 1400 1600 1800


De

fec

tio

n R

ate

(%

)

MFQ-SB-nAHA

Unfairness

0

1

2

3

4

5

6

7

8

600 800 1000 1200 1400 1600 1800


Un

fair

nes

s

MFQ-SB-nAHA

38

• Low Latency: requests must be served immediately

Challenges – conflicting goals

• Highly Efficient: each multicast must still be able to serve a large number of clients

39

Some Solutions• Application level:

– Piggybacking

– Patching

– Chaining

• Network level:

– Caching Multicast Protocol (Range Multicast)

40

Piggybacking [Golubchik96]

new arrivals

departures

+5% -5%C B A

•Slow down an earlier service and speed up the new one to merge them into one stream

•Limited efficiency due to long catch-up delay

•Implementation is complicated

41

Patching

RegularMulticast

Video

A

42

Proposed Technique: Patching

RegularMulticast

AVideo Player Buffer

B

Video

t

Patching Stream

Skew point

43

Proposed Technique: Patching

RegularMulticast

ABuffer

B

Video

2t

Skew point is absorbed by client buffer

Video Player

44

Client Design

Video

Server

Lr

VideoPlayer

Regular MulticastPatching Multicast

Data Loader

RegularStream

PatchingStream

Client A

LrLp

VideoPlayer

Client B

BufferLrLp

VideoPlayer

Client C

45

Server Design

Server must decide when to schedule a regular stream or a patching stream

A

r

B

p

C

p

D

p

E

r

F

p

G

p

Multicast group Multicast group

time

46

Two Simple Approaches

• If no regular stream for the same video exists, a new regular stream is scheduled

• Otherwise, two policies can be used to make decision: Greedy Patching and Grace Patching

47

Greedy Patching

Patching stream is always scheduled

Video Length

Shared Data

Buffer Size

Shared Data

Buffer Size

Shared Data

A

B

A

C

48

Grace Patching If client buffer is large enough to absorb the

skew, a patching stream is scheduled; otherwise, a new regular stream is scheduled.

Video Length

Buffer Size

Regular Stream

A

Shared DataB

C

49

Local Distribution Technologies

Video

Server

Video

Server

ATM or Sonet

backbone network

Switch

Switch

Localdistributionnetwork

Localdistributionnetwork

Client

Client

Client

Client

– ADSL (Asymmetric Digital Subscriber Line): currently 8 Mbps in one direction,

and eventually speeds as high as 50 Mbps

– HFC (Hybrid Fiber Coax): current 300-450 Mhz coax cables are replaced by

750 mhz coax cable to achieve a total of 2 Gbps

50

Performance Study

• Compared with conventional batching

• Maximum Factored Queue (MFQ) is used

• Two scenarios are studied

– No defection • average latency

– Defection allowed• average latency, defection rate, and unfairness

51

Simulation Parameters

Request rate (requests/min)

Client buffer (min of data)

Server bandwidth (streams)

Video length (minutes)

Number of videos

Parameter

50 10-90

5 0-10

1,200 400-1,800

90 N/A

100 N/A

Default Range

Video Access Skew factor 0.7 N/A

Number of requests 200,000 N/A

52

Effect of Server Bandwidth

Client BufferRequest RateDefection

5 minutes50 arrivals/minuteNo

0

100

200

300

400

500

600

400 600 800 1000 1200 1400 1600 1800

Ave

rage

Lat

ency

(Se

cond

s)

Server Communication BW (streams)

Conventional Batching

Greedy PatchingGrace Patching

53

Effect of Client Buffer

Server BandwidthRequest RateDefection

1,200 streams50 arrivals/minuteNo

0

20

40

60

80

100

120

140

160

180

200

0 1 2 3 4 5 6 7 8 9 10

Ave

rage

Lat

ency

(se

cond

s)

Client Buffer Size (minutes of data)



54

Effect of Request Rate

0

50

100

150

200

250

10 20 30 40 50 60 70 80 90 100 110

Ave

rage

Lat

ency

(se

cond

s)

Request Rate (requests/minutes)

Server BandwidthClient BufferDefection

1,200 streams5 minutesNo



55

Optimal Patching

A

r

B

p

C

p

D

p

E

r

F

p

G

p

patching window patching window

Multicast group Multicast group

time

What is the optimal patching window ?

56

Optimal Patching Window

• D is the mean total amount of data transmitted by a multicast group

• Minimize Server Bandwidth Requirement, D/W , under various W values

Video Length

Buffer Size Buffer Size

A

W

57

Optimal Patching Window

• Compute D, the mean amount of data transmitted for each multicast group

• Determine , the average time duration of a multicast group

• Server bandwidth requirement is D/ which is a function of the patching period

• Finding the patching period that minimize the bandwidth requirement

58

Candidates for Optimal Patching Window

59

Concluding Remarks

• Unlike conventional multicast, requests can be served immediately under patching

• Patching makes multicast more efficient by dynamically expanding the multicast tree

• Video streams usually deliver only the first few minutes of video data

• Patching is very simple and requires no specialized hardware

60

Patching on Internet

• Problem: – Current Internet does not support

multicast

• A Solution:

– Deploying an overlay of software routers on the Internet

– Multicast is implemented on this overlay using only IP unicast

61

Content Routing

RootRouter

RouterA

RouterB

RouterE

RouterC

RouterD

ClientClient

Find (1)Find (2)

Fin

d

RouterD

MyRouter ?

No

Yes

Server

Client

Videostream

Each router forwards its Find messages to other routers in a round-robin manner.

62

Removal of An Overlay Node

A

B

C

D

GF

E

Client

A

B

C

D

G

E

Client

Before adjustment After adjustment

Server Server

Inform the child nodes to reconnect to the grandparent

63

Failure of Parent Node

A

B

C

D

GF

E

Client

A

B

C

D

G

E

Client

After adjustmentBefore adjustment

– Data stop coming from the parent

– Reconnect to the server

64

Slow Incoming Stream

A

B

C

D

GF

E A

B

C

D

GF

E


Reconnect upward to the grandparent

65

Downward Reconnection

A

B

C

D

GF

E


A

B

C

D

GF

E

Slow

Slow

• When reconnection reaches the server, future reconnection of this link goes downward.

• Downward reconnection is done through a sibling node selected in a round-robin manner.

• When downward reconnection reaches a leave node, future reconnection of this link goes upward again.

66

Limitation of Patching

• The performance of Patching is limited by the server bandwidth.

• Can we scale the application beyond the physical limitation of the server ?

67

Chainin

g

• Using a hierarchy of multicasts• Clients multicast data to other clients

in the downstream• Demand on the server-bandwidth

requirement is substantially improved

Batch3

Batch1

Batch 2

A virtualbatch

Dedicated Channels Multicast Chaining

Only onevideo stream

3 videostreams

7 videostreams

client

Vid

eo

se

rve

r

Vid

eo

se

rve

r

Vid

eo

se

rve

r

Networkcache

68

Chaining

– Highly scalable and efficient

– But implementation is a challenge

Video Server

disk

Screen

disk

Screen

Screen

disk

Client A

Client B

Client C

69

Scheduling Multicasts

• Conventional Multicast

I State: The video has no pending requests. Q State: The video has at least one pending request.

• Chaining

C State: Until the first frame is dropped from the multicast tree, the tree continues to grow and the video stays in the C state.

I Q

request arrives

grant resources

requestarrives

I Q

request arrives

grantresources

requestarrives

C

requestarrives

dropthe firstframe

70

Enhancement

• When resources become available, the service begins for all the pending requests except for the “youngest” one.

• As long as new requests continue to arrive, the video remains in the E state.

• If the arrival of the requests momentarily discontinues for an extended period of time, the video transits into the C state after initiating the service for the last pending request.

E State:

grantresources

requestarrives

requestarrives

dropthe first

frame

I Q

request arrives

EC

request arrives

serve the lastpending request

• This strategy returns to the I state much less frequently.

• It is less demanding on the server bandwidth.

71

Advantages of Chaining• Requests do not have to wait for the next

multicast.

– Better service latency

• Clients can receive data from the expanding multicast hierarchy instead of the server.

– Less demanding on server bandwidth

• Every client that uses the service contributes its resources to the distributed environment.

– Scalable

72

Chaining is Expensive ?

• Each receive end must have caching space.

• 56 Mbytes can cache five minutes of MPEG-1 video

• The additional cost can easily pay for itself in a short time.

73

Limitation of Chaining

• It only works for a collaborating environment

i.e., the receiving nodes are on all the time

• It conserves server bandwidth, but not network bandwidth.

74

Another Challenge

• Can a multicast deliver the entire video to all the receivers who may subscribe to the multicast at different times ?

• If we can achieve the above capability, we would not need to multicast too frequently.

75

Range Multicast [Hua02]

• Deploying an overlay of software routers on the Internet

• Video data are transmitted to clients through these software routers

• Each router caches a prefix of the video streams passing through

• This buffer may be used to provide the entire video content to subsequent clients arriving within a buffer-size period

76

Range Multicast Group Caching Multicast Protocol (CMP)

C1 C3

C4 C2VideoServer

0

7

8

110

0

0

7

7

7

8

8

11

R5

R6R3

R4R1 R7

R8R2

Root

• Four clients join the same server stream at different times without delay

• Each client sees the entire video

Buffer Size: Each router can cache 10 time units of video data.

Assumption: No transmission delay

77

Multicast Range

• All members of a conventional multicast group share the same play point at all time

– They must join at the multicast time

• Members of a range multicast group can have a range of different play points

– They can join at their own time Multicast Range at time 11: [0, 11]

C1 C3

C4 C2VideoServer

0

7

8

110

0

0

7

7

7

8

8

11

R5

R6R3

R4R1 R7

R8R2

Root

78

Network Cache Management

• Initially, a cache chunk is free.

• When a free chunk is dispatched for a new stream, the chunk becomes busy.

• A busy chunk becomes hot if its content matches a new service request.

free

busy

hot

New streamarrives

A servicerequest arrivesbefore the chunkis full

Lastserviceends

A servicerequest arrives

before the chunkis full

Replacedby a newstream

79

CMP vs. Chaining

VideoServer

RouterR1

RouterR2

RouterR3

RouterR4

RouterR10

RouterR5

RouterR8

RouterR9

RouterR6

RouterR7

C1

C3

C4 C2

0

7

8

11

11

7

7

7

8

8

0

0

0

0

7

7

8

88

11

11

11 11

8

8

7

11

VideoServer

RouterR1

RouterR2

RouterR3

RouterR4

RouterR10

RouterR5

RouterR8

RouterR9

RouterR6

RouterR7

C1

C3

C4 C2

0

7

8

11

11

7

7

7

8

8

0

0

0

0Chaining CMP

Assumption: Each router has one chunk of storage space

capable of caching 10 time units of video.

80

CMP vs. Proxy Servers

Proxy servers are placed at the edge of the network to serve local users.

CMP routers are located throughout the network for all users to share.

Proxy servers are managed autonomously.

The router caches are seen collectively as a single unit.

Proxy Servers CMP

81

CMP vs. Proxy Servers

Popular data are heavily duplicated if we cache long videos.

CMP routers cache only a small leading portion of the video passing through

Caching long videos is not advisable. Many data must still be obtained from the server

Majority of the data are obtained from the network.

Proxy Servers CMP

82

VCR-Like Interactivity

• Continuous Interactive functions– Fast forward– Fast rewind– Pause

• Discontinuous Interactive functions– Jump forward– Jump backward

Useful for many VoD applications

VCR Interaction Using Client Buffer

Play PointN N + 20

N+2 N+22

N+4 N+24

Before

Play

Pause

4X Fast ForwardN+6 N+26

N+6 N+26

Jump Backward

Video stream

Video stream

Video stream

Video stream

Video stream

84

Interaction Using Batching [Almeroth96]

• Requests arriving during a time slot form a multicast group

• Jump operations can be realized by switching to an appropriate multicast group

• Use an emergency stream if a destination multicast group does not exist

Emergency Stream

Batching Period time

Ju

mp

Ju

mp

Ju

mp

Continuous Interactivity under

Batching• Pause:

– Stop the display– Return to normal play as in Jump

• Fast Forward:– Fast forward the video frames in the

buffer– When the buffer is exhausted, return to

normal play as in Jump

• Fast Rewind:– Same as in fast forward, but in reverse

direction

SAM (Split and Merge) Protocol [Liao97]

• Uses 2 types of streams, S streams for normal multicast and I streams for interactivity.

• When a user initiates an interactive operation:– Use an I channel to interact with the video

– When done, use the I channel as a patching stream to join an existing multicast

– Return the I channel

Advantage: Unrestricted fast forward and rewind

Disadvantage: I streams require substantial bandwidth

87

Resuming Normal Play in SAM

62 5431

762 5431

762 5431

762 5431

Original S Stream

Ineligible S StreamSegment 6 is in the future

NowPoint to resumenormal play

Targeted S StreamEnough buffer to cache

segments 8 and 9

d

Ineligible S Streamd > buffer size, patching cannot help

d

• Use the I stream to download segments 6 and 7, and render them onto the screen

• At the same time, join the target multicast and cache the data, starting from segment 8, in a local buffer

88

Interaction with Broadcast Video

• The interactive techniques developed for Batching can also be used for Staggered Broadcast

• However, Staggered Broadcast does not perform well

89

Client Centric Approach (CCA)

• Server broadcasts each segment at the playback rate

• Clients use c loaders

• Each loader download its streams sequentially, e.g., i th loader is responsible for segments i, i+c, i+2c, i+3c, …

• Only one loader is used to download all the equal-size W-segments sequentially

W

Channel 1

Channel 2

Channel 3

Channel 4

Channel 5

Channel K

Group 1

Group 2

Group i

C = 3 (Clients have three loaders)

.1)(mod)1(

,1)(mod)1(2

,11

)(

cnnf

cnnf

n

nf

90

CCA is Good for Interactivity

• Segments in the same group are downloaded at the same time

– Facilitate fast forward

• The last segment of a group is of the same size as the first segment of the next group

– Ensure smooth continuous playback after interactivity

Broadcast point

Seg 1 of size 1

Seg 2 of size 2

Seg 3 of size 2

Seg 4 of size 5

Seg 5 of size 5

Seg 6 of size 12

Seg 7 of size 12

Gr 1

Gr2

Gr3

Gr4

After a Jump Action : Skyscraper does not guarantee a smooth play back

Broadcast point

Group 1

Group2

Group3

After a Jump Action : CCA technique always guarantees a smoth play back

Desired destination point

Actual destination point

Downloaded by Odd Loader

Downloaded by Even Loader

Missing data

Desired destination point

Actual destination pointDownloaded byLoader 3

Downloaded byLoader 1

91

Broadcast-based Interactive Technique (BIT) [Hua02]

Cr1

Cr2

Cr3

Cr4

Ci1

Cr5

CrKr-3

CrKr-2

Crkr-1

CrKr

Ciki

W

Group 1

Group Ki

An interactivechannel

broadcasts acompressed

version of thedata in the

group

92

BITEnd ofvideo ?

Render next framein Normal Buffer

Interactioninitiated ?

Continuousoperation ?

Destination point inNormal Buffer ?

Render next frame inInteractive Buffer

Resumenormal play ?

Interactive Bufferexhausted ?

Load appropriate group to keep resume point near “middle” of Normal Buffer

Jump todestination point

No

Yes

No

Yes

No

Yes

Yes

No

No

No

Yes

YesEND

BEGIN

• Two Buffers– Normal Buffer

– Interactive Buffer

• When Interactive Buffer is exhausted, client must resume normal play

93

BIT – Resume-Play Operation

case 1 case 2

Broadcast point Broadcast point


Desired destination

Desired destination

Desireddestination


Desired destination Desired destination

case 3 case 4

case 5 case 6

i

i + 1

i + 2

i

i + 1

i + 2

i

i + 1

i + 2

i

i + 1

i + 2

i

i + 1

i + 2

i

i + 1

i + 2

i

i + 1

i + 2

i

i + 1

i + 2

Destination point Desired destination

case 7 case 8


Actualdestination

Actualdestination

Desired destination

Actualdestination

Actualdestination

Actualdestination

Actualdestination

Actualdestination

Actualdestination

Three segments are being downloaded simultaneously

Actual destination point is chosen from among frames at broadcast point to ensure continuous playback

94

BIT - User Behavior Model

Playmp

Fast Reversemfr

Fast Forwardmff

Pausempause

JumpForward

mjf'

JumpBackward

mjb'

1

1

11

1

Pplay

Pfr

Pff

Ppause

Pjb Pjf

• mx: duration of action x• Px: probability to issue action x• Pi: probability to issue

interaction• mi: duration of the interaction• mff = mfr = mpause = mjf = mjb, • Ppause = Pff = Pfb = Pjf = Pjb = Pi/5. • dr : mi/mp interaction ratio.

Performance Metrics

• Percentage of unsuccessful action

– Interaction fails if the buffer fails to accommodate the operation

– E.g., a long-duration fast forward pushes the play point off the Interactive Buffer

• Average Percentage of Completion

– Measure the degree of incompleteness

– E.g., if a 20-second fast forward is forced to resume normal play after 15 seconds, the Percentage of Completion is 15/20, or 75%.

96

BIT - Simulation

Results

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

0.5 1 1.5 2 2.5 3 3.5

Duration ratio

Ave

rage

Per

cent

age

of C

ompl

etio

n

Active BufferManagement

BIT

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.5 1 1.5 2 2.5 3 3.5

Duration ratio

Perc

enta

ge o

f Uns

ucce

ssfu

l Act

ions

Active BufferManagement

BIT

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

1 2 3 4 5 6 7

regular buffer size

Per

cent

age

of U

nsuc

cess

ful A

ctio

ns

A.B.M, d_ratio =1

BIT, d_ratio =1

A.B.M, d_ratio =1.5

BIT, d_ratio = 1.5

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1 2 3 4 5 6 7

regular buffer size

Ave

rage

Per

cent

age

of C

ompl

etio

n

A.B.M, d_ratio =1

BIT, d_ratio 1

A.B.M, d_ratio =1.5

BIT, d_ratio = 1.5

97

Support Client Heterogeneity

• Using multi-resolution encoding

• Bandwidth Adaptor

• HeRO Broadcasting

98

Multi-resolution Encoding

• Encode the video data as a series of layers

• A user can individually mould its service to fit its capacity

• A user keeps adding layers until it is congested, then drops the higher layer

Drawback: Compromise the display quality

99

Bandwidth Adaptors

Video Server

ClientClientClient

Bandwidth Adaptor

Averagebandwidth

Averagebandwidth

More bandwidth

Client

Client

Bandwidth Adaptor

Bandwidth Adaptor

Client

Less bandwidth

Even less bandwidth

Even less bandwidth

Server-end Adaptor

Client-end Adaptor

Advantage: All clients enjoy the same quality display

100

Requirements for an Adaptor

• An adaptor dynamically transforms a given broadcast into another less demanding one

• The segmentation scheme must allow easy transformation of a broadcast into another

• CCA segmentation technique has this property

101

Two Segmentation Examples

102

Adaptation (1)

Server

Sender routine 1

Sender routine 2

Sender routine Ks

Segment 1

Segment 2

Segment Ks

Adaptor

Channel 1

71 70 69

Segment 1

Buffer space

68

InsertChunk(68)?

Yes

No. Ignore chunk.

Loader Routine 1

Adaptor downloads from all broadcast channels simultaneously

103

Adaptation (2)

Adaptor

Sender routine KaSegment Ka

369 368 367

DeleteChunk(370)?

No. Just send.

Yes. Send anddelete from buffer.

• Each sender routine retrieves data chunks from buffer, and broadcast them to the downstream

• For each chunk, the sender routine calls deleteChunk to decide if the chunk can be deleted from the buffer

104

Buffer Management

• insertChunk implements an As Late As Possible policy, i.e.,

– If another occurrence of this chunk will be available from the server before it is needed, then ignore this one, else buffer it.

• deleteChunk implements an As soon As Possible policy, i.e.,

– Determine the next time when the chunk will need to be broadcast to the downstream.

– If this moment comes before the availability of the chunk at the server, then keep it in storage, else delete it.

105

The Adaptor Buffer

• Computation is not intensive.

• It is only performed for the first chunk of the segment, i.e.,

– If this initial chunk is marked for caching, so will be the rest of the segment.

• Same thing goes for deletion.

106

The start-up delayThe start-up delay is the broadcast period of

the first segment on the server

107

HeRO – Heterogeneous Receiver-Oriented

Broadcasting • Allows receivers of various

communication capabilities to share the same periodic broadcast

• All receivers enjoy the same video quality

• Bandwidth adaptors are not used

108

HeRO – Data Segmentation

• The size of the i th segment is 2i-1 times the size of the first segment

109

HeRO – Download Strategy

• The number of channels needed depends on the time slot of the arrival of the service request

• Loader i downloads segments i, i+C, i+2C, i+3C, etc. sequentially, where C is the number of loaders available.

Global Period

110

HeRO – Regular Channels

• The first user can download from six channels simultaneously

Request 1

111

HeRO – Regular Channels

• The second user can download from two channels simultaneously

Request 2

112

Worst-Case for Clients with 2 loaders

• Worst-case latency is 11 time units

• The worst-cases appear because the broadcast periods coincide at the end of the global period

Request 2

Coincidence of the broadcast periods

11 time units

113

Worst-Case for Clients with 3 loaders

• Worst-case latency is 5 time units

• The worst-cases appear because the broadcast periods coincide at the end of the global period

Request

5 time units

Coincidence of the broadcast periods

114

Observations of Worst-Cases

• For a client with a given bandwidth, the time slots it can start the video are not uniformly distributed over the global period.

• The non-uniformity varies over the global period depending on the degree of coincidence among the broadcast periods of various segments.

115

Observations of Worst-Cases (cont…)

• The worst non-uniformity occurs at the end of each global period when the broadcast periods of all segments coincide.

• The non-uniformity causes long service delays for clients with less bandwidth.

We need to minimize this coincidence to improve the worst case.

116

• We broadcast the last segment on one more channel, but with a time shift half its size.

• We now offer more possibilities to download the last segment; and above all, we eliminate every coincidence with the previous segments.

RegularGroup

ShiftedChannel

Adding one more channel

117

ShiftedChannels

• To reduce service latency for less capable clients, broadcast the longest segments on a second channel with a phase offset half their size.

Channel 1Channel 2Channel 3Channel 4Channel 5a

0 1 2 3 4 5 6 7 8 9 1110 1312 1514 1716 18 2019 2221 2423 25 2726 2928 3130 32Shift = D5/2

Channel 5bChannel 6aChannel 6b

Shift = D6/2The t unit is D1

t

4 1 2 2 3 2 2 3 4 2 2 2 3 2 2 3 4 1 2 2 3 2 2 3 4 2 2 2 3 2 2 3

HeRO

118

• Under a homogeneous environment, HeRO is

– very competitive in service latencies compared to the best protocols to date

– the most efficient protocol to save client buffer space

• HeRO is the first periodic broadcast technique designed to address the heterogeneity in receiver bandwidth

• Less capable clients enjoy the same playback quality

HeRO – Experimental Results

119

2-Phase Service Model(2PSM)

Browsing Videos in a Low Bandwidth Environment

120

Search Model

• Use similarity matching (e.g., keyword search) to look for the candidate videos.

• Preview some of the candidates to identify the desired video.

• Apply VCR-style functions to search for the video segments.

121

Conventional Approach

Advantage: Reduce wait time

1. Download So

2. Download S1

while playing S0

3.Download S2

while playing S1...

Disadvantage:Unsuitable for video libraries.

S 1 S 2 S 3 ...

...

display S 0

display S 1

display S 2

S0

S 1

S 2

S 3

Server

Client

S0

Time

122

Search Techniques

• Use extra preview files to support the preview function.

• Use separate fast-forward and fast-reverse files to provide the VCR-style operations.

• It requires more storage space.• Downloading the preview file adds delay to the service.

• It requires more storage space.• Server can becomes a bottleneck.

123

Challenges

How to download the preview frames for FREE ?

No additional delay

No additional storage requirement

How to support VCR operations without VCR files ?

No overhead for the server

No additional storage requirement

124

2PSM – Preview Phase

0

1

2

3

4

6

7

8

9

10

12 18

13

14

15

16

5 11 17

19

20

21

22

23

25

26

27

28

29

24 30 36 42 48

31

32

33

34

35

37

38

39

40

41

43

44

45

46

47

54 60 66 72 78 84 90

49

50

51

52

53

55

56

57

58

59

61

62

63

64

65

67

68

69

70

71

73

74

75

76

77

79

80

81

82

83

85

86

87

88

89

91

92

93

94

95

96

97

98

99

100

102

103

104

105

106

108 114

109

110

111

112

101 107 113

115

116

117

118

119

121

122

123

124

125

120 126 132 138 144

127

128

129

130

131

133

134

135

136

137

139

140

141

142

143

150 156 186162 168 174 180

145

146

147

148

149

151

152

153

154

155

158

157

189159

190160

187

161

188

191

163

164

165

166

167

169

170

171

172

173

175

176

177

178

179

181

182

183

184

185

downloadedduring Step 1



L

R

.

.

.

.

.

.

.

.

.

GOFs available for previewing after 3 steps

The preview quality improves gradually.

.

.

.

90

1146618

42

162

138

1741501261027854306downloaded

during Step 4

125

2PSM – Playback PhaseServer

. . .PU0 PU1 PU2 PU3 PU4 PU5 PU6

L3 L4 L5 L6

L

0 L1

L2

L3

L4

L5

L6

L7

L7R2 R3

R

5

R6

R

1

R

0

R

2 R

3 R

4

R4 R5

R

6

PU0

Client

Download during Initialization Phase Download during Playback Phase

PU1

. . .

display

display

display

display

display

display

display

PU2

PU3

PU4

PU5

PU6

R0L0L1

R1 L2

t

126

Remarks

1. It requires no extra files to provide the preview feature.

2. Downloading the preview frames is free.

3. It requires no extra files to support the VCR functionality.

4. Each client manages its own VCR-style interaction. Server is not involved.

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