prefix caching assisted periodic broadcast for streaming popular videos yang guo, subhabrata sen,...
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Prefix Caching assisted Periodic Broadcast for Streaming Popular Videos
Yang Guo, Subhabrata Sen, and Don Towsley
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Outline
Introduction Previous works Prefix caching assisted periodic
broadcast Evaluation Conclusion
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Introduction
Digital video Bandwidth-intensive Long-lived Large size
Challenging problem Bandwidth-efficient distribution of
heterogeneous videos to such a large, asynchronous client population
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Introduction Multicast or broadcast connection
Example: periodic broadcast and patching Reducing server loads, network traffic Providing a guaranteed bound on a client’s
startup latency Proxy
Example: caching a initial prefix of the video Reducing server loads, network traffic and
access latency
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An Internet Content Distribution Network
cheaper
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Proxy Caching
1. Treating multimedia streams as sequences of non-overlapping segments.
2. Dividing the streams into multiple layers of quality information.
3. Prefetching initial portions of the streams.
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Proxy Caching Example(1)
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Proxy Caching Example(2)
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Skyscraper Broadcasts
Constraint For any initial unit segment broadcast
, there must be a sequence of segments that the client can receive that will support continuous playback to the viewer
Clients are required to receive data on no more than two channels simultaneously
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Skyscraper Broadcasts
Progression
We use W to restrict the segments from becoming too large. EX:W= 12
[ 1 , 2 , 2 , 5 , 5 , 12 , 12 , 12 , 12…]
Storage Requirement: (W-1)
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Prefix caching assisted periodic broadcast 1. we determine the appropriate suffix
transmission scheme (periodic broadcast) that minimizes the aggregate bandwidth usage on the server-proxy path.
2. for each proxy, an appropriate prefix transmission scheme (combination of patching and periodic broadcast) is determined, based on the relative popularity of a video among clients of that proxy.
3. we present a greedy algorithm to determine the allocation of the proxy buffer space that the aggregate bandwidth usage on the server-proxy network path is minimized.
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Distributing a single video
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Distributing a single video
Broadcast suffix
Request videoRequest prefix
Prefix streamsend prefix data
Select cachingSkyscraper Broadcast
Buffer suffix
send suffix data
Segment 1
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Distributing a single video-patch stream
Broadcast suffix
Request videoRequest patch stream
Patch stream
send prefix data
Select cachingSkyscraper Broadcast
Buffer suffix
send suffix data
Segment 1
Prefix streamsend Patch data
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Distributing a single video Buffer Usage
Main for suffix transmission Skyscraper : W-1 units Fast Data Broadcast : about half of video
Prefix Length To ensure seamless transition when the
client switches from playing back the prefix to the suffix, it should start receiving the suffix before the end of prefix is reached
The first segment of the suffix cannot be larger than the prefix
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Optimal proxy buffer allocation channel swapping
We minimize the buffer usage without changing the total number of long-haul channels required.
Video i that has the minimum increase of prefix size to multicast video using one less channel.
Video j that has the maximum decrease of prefix size to multicast video using one more channel
If the increase of video i is less than the decrease of video j , we offer more buffer to video i so that it used one less channel while taking away some buffer from video j so that it uses one more channel.
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Bandwidth vs. buffer size
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Prefix percentage of video length
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Optimal buffer allocation
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Comparison with optimized regional caching
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Conclusion Methodology
optimally allocating the proxy buffer space choosing appropriate prefix and suffix
transmission schemes The framework is scalable, flexible, and
supports popular video streaming with small playback delay.
Feature work extending our work to support VBR video
delivery exploring our framework in a realistic
network setting