Realtime Multimedia Caching Schemes

Several caching schemes for realtime multimedia systems have been proposed but they have only concentrated on the hit ratio as a performance metric without providing any means to utilize the disk bandwidth gained through cache hits. A high cache hit ratio alone does not capture the eeectiveness of a caching scheme for such systems unless hiccup-free service is guaranteed. We evaluate four caching schemes which make it possible to provide service to additional streams with the saved disk bandwidth. We rst present the SPT-L scheme, which has a signiicant overhead accompanied by the best hit ratio. STP-L suuers from frequent starvation, which supports our claim that a high cache hit ratio alone does not necessarily result in better performance. Next, we propose the NIC scheme in which no cached intervals are preempted or replaced unless they have nished their playback. We also propose the PSIC scheme, which preempts the cached intervals for more valuable intervals but still guarantees hiccup-free playback. Although PSIC shows good performance without much overhead, the cache ratio needs to be determined in advance. Since the optimal cache hit ratio is not easy to obtain and can vary dynamically depending on the workload situation, we present the DIC scheme in which cache ratio is adjusted according to the state of the systems.