Prefix Caching assisted Periodic Broadcast for Streaming Popular Videos

Yang Guo, Subhabrata Sen, and Don Towsley

Outline

Introduction Previous works Prefix caching assisted periodic

broadcast Evaluation Conclusion

Introduction

Digital video Bandwidth-intensive Long-lived Large size

Challenging problem Bandwidth-efficient distribution of

heterogeneous videos to such a large, asynchronous client population

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

An Internet Content Distribution Network

cheaper

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.

Proxy Caching Example(1)

Proxy Caching Example(2)

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

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)

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.

Distributing a single video

Distributing a single video

Broadcast suffix

Request videoRequest prefix

Prefix streamsend prefix data

Select cachingSkyscraper Broadcast

Buffer suffix

send suffix data

Segment 1

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

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

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.

Bandwidth vs. buffer size

Prefix percentage of video length

Optimal buffer allocation

Comparison with optimized regional caching

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