CostEffective Video Streaming Techniques

1
Cost-Effective Video Streaming Techniques

• Kien A. Hua
• School of EE Computer Science
• University of Central Florida
• Orlando, FL 32816-2362
• U.S.A

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
Dedicated stream
Client
Client
Client
Client
Too Expensive !
4
Batching

• FCFS
• MQL (Maximum Queue Length First)
• MFQ (Maximum Factored Queue Length)

Can multicast provide true VoD ?
5
Challenges conflicting goals

• Low Latency requests must be served immediately

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

6
Some Solutions

• Patching Hua98
• Range Multicast Hua02

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Patching
Video
Regular Multicast
A
8
Proposed Technique Patching
Skew point
Video
t
Patching Stream
Regular Multicast
A
9
Proposed Technique Patching
Video
2t
Regular Multicast
Skew point is absorbed by client buffer
Buffer
Video Player
A
B
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Client Design
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Server Design

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

time
r
p
p
p
r
p
p
A
B
C
D
E
F
G
Multicast group
Multicast group
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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

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Greedy Patching

• Patching stream is always scheduled

Time
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Grace Patching

• If client buffer is large enough to absorb
  the skew, a patching stream is scheduled
  otherwise, a new regular stream is scheduled.

Time
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Performance Study

• Compared with conventional batching
• Maximum Factored Queue (MFQ) is used
• Performance metric is average service latency

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Simulation Parameters
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Effect of Server Bandwidth
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Effect of Client Buffer
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Effect of Request Rate
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Optimal Patching
time
patching window
patching window
r
p
p
p
r
p
p
A
B
C
D
E
F
G
Multicast group
Multicast group
What is the optimal patching window ?
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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

Buffer Size
Buffer Size
Video Length
A
W
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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

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Candidates for Optimal Patching Window
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Piggybacking Golubchik96

• Slow down an earlier service and speed up the new
  one to merge them into one stream
• Limited stream sharing due to long catch-up delay
• Implementation is complicated

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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

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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

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Content Routing

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

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Removal of An Overlay Node
Inform the child nodes to reconnect to the
grandparent
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Failure of Parent Node

• Data stop coming from the parent
• Reconnect to the server

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Slow Incoming Stream
Reconnect upward to the grandparent
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Downward Reconnection

• 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.

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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 ?

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Chaining Hua97

• Using a hierarchy of multicasts
• Clients multicast data to other clients in the
  downstream
• Demand on server bandwidth is substantially
  reduced

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Chaining

• Highly scalable and efficient
• Implementation is complex

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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

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Range Multicast Group

• 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
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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
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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.

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RM vs. Proxy Servers
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2-Phase Service Model(2PSM) Hua99Browsing
Videos in a Low Bandwidth Environment
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Search Model

• Use similarity matching or 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.

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Conventional Approach
1. Download So
2. Download S1
while playing S0
3.
Download S2
while playing S1
.
.
.
Advantage
Reduce wait time
Disadvantage
Unsuitable for searching video
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Search Techniques

• Use extra preview files to support the preview
  function
• Requires more storage space
• Downloading the preview file adds delay
• Use separate fast-forward and fast-reverse files
  to provide the VCR-style operations
• Requires more storage space
• Server can become a bottleneck

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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
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2PSM Preview Phase
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2PSM Playback Phase
t
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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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2PSM Video Browser