1. Prefix Caching assisted Periodic Broadcast for Streaming Popular Videos Yang Guo, Subhabrata Sen, and Don Towsley

2. Outline Introduction Previous works Prefix caching assisted periodic broadcast Evaluation Conclusion

3. Introduction Digital video Bandwidth-intensive Long-lived Large size Challenging problem Bandwidth-efficient distribution of heterogeneous videos to such a large, asynchronous client population

4. 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

5. An Internet Content Distribution Network cheaper

6. 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.

7. Proxy Caching Example(1)

8. Proxy Caching Example(2)

9. 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

10. 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)

11. 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.

12. Distributing a single video

13. Broadcast suffix Request video Request prefix Prefix stream send prefix data Select cachingSkyscraper Broadcast Buffer suffix send suffix data Segment 1

14. Distributing a single video -patch stream Broadcast suffix Request video Request patch stream Patch stream send prefix data Select cachingSkyscraper Broadcast Buffer suffix send suffix data Segment 1 Prefix stream send Patch data

15. 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

16. 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.

17. Bandwidth vs. buffer size

18. Prefix percentage of video length

19. Optimal buffer allocation

20. Comparison with optimized regional caching

21. 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