Cost analyses for VBR video servers

Abstract

In this paper we compare techniques for storage and real-time retrieval of Variable Bit Rate (VBR) video data for multiple simultaneous users. The motivation for considering VBR is that video results in inherently time varying data, and as such, with the same average bit rate, higher quality can be achieved with VBR than with Constant Bit Rate (CBR). We propose and compare the following three classes of VBR data placement and retrieval techniques: Constant Time Length (CTL) places and retrieves data in blocks corresponding to equal playback durations, Constant Data Length (CDL) places and retrieves constant-sized data blocks, and a hybrid solution uses CDL placement but retrieves a variable number of blocks in each service round. We have found that CTL data placement has much lower bu er requirements than CDL but su ers from fragmentation during video editing. We show hybrid placement to have both advantages of high e ciency and low fragmentation.We also address the issue of admission control policies by comparing statistical and deterministic techniques. \Statistical" admission control uses statistics of the stored data to ensure that the probability of \overload" does not exceed a prespeci ed threshold. \Deterministic" control uses the actual stored video bit traces to regulate the number of admitted users. We consider two types of deterministic admission control: data-limit and ideal deterministic. Data-limit admission control admits users based on precomputing the total amount of data requested by all users in future service rounds. In contrast, Ideal deterministic admission control not only precomputes the total amount of data requested, but also assumes we have control of data placement at the disk sector level in order to precompute the future seek and rotation times.We provide a cost/bene t analysis of the above placement/retrieval/admission control techniques and conclude that CTL and hybrid placement/retrieval techniques can reduce the total system cost by up to a factor of 3 in comparison with the strategy of padding the VBR video trace to achieve a constant data rate. For read-only systems, CTL has the lowest cost per user. For writable systems, the hybrid technique achieves a good compromise between low cost and low fragmentation. We nd that all forms of deterministic admission control can outperform statistical, but the greatest gain comes from using ideal deterministic admission control. We note, however, that this admission control may be di cult to implement on standard disk controllers. Finally, we have implemented a full disk model simulator that operates 1000 times faster than the real-time disk. Results using the simulator are very close to those measured on the real disk, making the simulator useful for future experiments.

Design and analysis of a demand adaptive and locality aware streaming media server cluster

“…A number of admission control algorithms have been proposed recently [22,12,49]; any such algorithm suffices for this purpose. Note that it is desirable to reserve a small fraction of bandwidth resource (e.g., that corresponds to one streaming session) for control messages such as for token passes.…”

“…This work targeted a variety of topics such as admission control [22,12], scheduling [49], striping [47,31,28] and caching [21].…”

Efficient memory management in video on demand servers

“…This model, in disk-bounded systems, should involve precise estimations of disk seek times, rotation times, and transfer speeds. An admission control algorithm that employs this highly detailed information model is called ideal deterministic [4].…”

Adaptive QoS Control Based on Benefit Optimization for Video Servers Providing Differentiated Services

“…Over the past few years, there has been substantial research effort in the area of QoS control schemes working toward this goal. On the server end, various algorithms have been proposed to optimize disk bandwidth allocations for effectively servicing multiple requests by means of admission control and data placement schemes [3]. The goal is either to reduce the overall cost per request or to maximize the maximum number of requests the system is able to service simultaneously with statistical or absolute QoS guarantees.…”