Caching Strategies in Transcoding-Enabled Proxy System for Streaming Media Distribution Networks Bo Shen Sung-Ju Lee Sujoy Basu IEEE Transactions On Multimedia, April 2004

Outline Introduction Transcoding-Enabled Caching System Architecture Transcoding-Enabled Caching Algorithms Other Proxy Caching Algorithms Performance Analysis Conclusion

Introduction Traditional Proxy Caching Video 1 (1) 64 kbps (2) 128 kbps (3) 256 kbps Video 2 (1) 64 kbps (2) 128 kbps ………… ………… Server Proxy Video 1 (1) 64 kbps (2) 128 kbps (3) 256 kbps Video 2 (1) 64 kbps (2) 128 kbps ………… ………… Desktop Client Cell Phone PDA Video kbps Video 1 64 kbps Video kbps PDA Video kbps Video 1 (1) 64 kbps (2) 128 kbps (3) 256 kbps Video 2 (1) 64 kbps (2) 128 kbps ………… …………

Introduction TEC Purpose Transcoding-enabled Catching (TEC) proxy system is designed for efficient delivery of rich media web content to heterogeneous network and client capabilities. Save cache size of proxy.

Introduction Other method for heterogeneous client Scalable coding and layered coding –Majority if not all of the current multimedia content on the Internet is coded in nonscalable, single- layered format.

TEC System Architecture

TEC System Architecture Transcoding Techniques A higher bit-rate version can be transcoded to a lower bit-rate version. The transcoded version may have fidelity degradation compared with the original version. Compressed domain transcoding –Bit-rate reduction transcoding –Spatial resolution reduction transcoding

TEC System Architecture Transcoding Techniques Bit-rate reduction transcoding Faster than a decode-and-re-encode approach

TEC System Architecture Transcoding Techniques Spatial resolution reduction transcoding –Transcoder obtains motion information for the down-sampled video directly from the orginal video. TEC System uses bit-rate reduction model

TEC Algorithm Exact hit : the requested version of the video object exists in the cache. Transcode hit : the requested version does not exist in the cache, but a transcodable version of the video exists. Miss : the requested or transcodable version of the video does not exist in the cache.

TEC Algorithm TEC 11 Video 1 (1) 64 kbps (2) 128 kbps (3) 256 kbps Video 2 (1) 64 kbps (2) 128 kbps ………… ………… Server PDA Video 1 (1) 64 kbps (2) 128 kbps (3) 256 kbps Video 2 (1) 64 kbps (2) 128 kbps ………… ………… Proxy Request V1 128 kbps Exact hit V1 128 kbps Request V1 256 kbps V1 256 kbps Miss Video 1 (1) 64 kbps (2) 128 kbps (3) 256 kbps Video 2 (1) 64 kbps (2) 128 kbps ………… ………… If cache size is not enough, use LRU replacement Cache Single Version of Video V1 256 kbps is trancoded to V1 128 kbps

TEC Algorithm TEC 12 Video 1 (1) 64 kbps (2) 128 kbps (3) 256 kbps Video 2 (1) 64 kbps (2) 128 kbps ………… ………… Server PDAProxy Video 1 (1) 64 kbps (2) 128 kbps (3) 256 kbps Video 2 (1) 64 kbps (2) 128 kbps ………… ………… Cache Single Version of Video Request V1 128 kbps V1 256 kbps is trancoded to V1 128 kbps Video 1 (1) 64 kbps (2) 128 kbps (3) 256 kbps Video 2 (1) 64 kbps (2) 128 kbps ………… ………… V1 128 kbps

TEC Algorithm TEC 2 Video 1 (1) 64 kbps (2) 128 kbps (3) 256 kbps Video 2 (1) 64 kbps (2) 128 kbps ………… ………… Server PDAProxy Cache Multiple Version of Video Video 1 (1) 64 kbs (2) 128 kbps (3) 256 kbps Video 2 (1) 64 kbps (2) 128 kbps ………… ………… Request V1 64 kbps (1) V1 128 kbps is transcoded to 64 kbps (2)cache 64 kbps, if cache size is not enough, use LRU Video 1 (1) 64 kbps (2) 128 kbps (3) 256 kbps Video 2 (1) 64 kbps (2) 128 kbps ………… ………… Request V1 256 kbps Cache V1 256 kbps, if cache is not enough, use LRU replacement Video 1 (1) 64 kbps (2) 128 kbps (3) 256 kbps Video 2 (1) 64 kbps (2) 128 kbps ………… …………

Other Proxy Cache Algorithm Video 1 (1) 64 kbps (2) 128 kbps (3) 256 kbps Video 2 (1) 64 kbps (2) 128 kbps ………… ………… Server PDAProxy Video 1 (1) 64 kbps (2) 128 kbps (3) 256 kbps Video 2 (1) 64 kbps (2) 128 kbps ………… ………… Request V1 64 or 128 kbps Transcoding from V1 256 kbps FVO (Full Version Only)

Other Proxy Cache Algorithm TVO (Transcoded Version Only) : Always caching the transcoded objects, and if a request does not result in an exact hit, the full version is fetched from the origin to produce a transcoded version. LRU : Caching all video across proxy without any transcoding, if cache size is not enough, using LRU replacement.

Performance Analysis Highly Heterogeneous Environment Video version : Origin server has 512 kbps, 256 kbps, 128 kbps, 64 kbps The full version is not requested by the clients, but could be accessed by the proxy when FVO or TVO are used. Byte hit ratio : The number of bytes served from the cache to the clients over the number of bytes requested from the client Relative cache size : Dividing the cache size by the size summation of total unique objects.

Performance Analysis Highly Heterogeneous Environment Indicates the transcoding load each algorithm requires

Performance Analysis Highly Heterogeneous Environment Quality degradation less than 1 dB

Performance Analysis D miss D ehit D thit CIF339 ms127 ms173 ms QCIF185 ms35 ms42 ms

Conclusion TEC improves the cache effectiveness, decreases the user-perceived latency, and reduces the traffic between the proxy and the content origin server. TEC-2 gave good performances when the caches size is large. TEC-11 generally showed the highest byte-hit ratio but also had the highest transcoding load.