| A real HD-VOD experimental system has big hardware investment, high cost of operation and maintenance, time consuming in setting up the test environment, and strict limitation in the test scale, whereas a VOD simulator has the outstanding advantage of low cost, high efficiency, and the capacity for making large-scale tests. Therefore a VOD simulator could be a powerful research tool. This paper designs and implements a HD-VOD simulator, which has rather good practicability, functionality, ease of use, and extensibility. The followings are the main functions and characteristics of the simulator. It contains two kinds of HD-VOD systems, one of which employs video replication, and the other in which videos are striped and stored across every resource disks (abbreviation for "striped HD-VOD" in the below). The client part can simulate the behavior of client’s replay and simulate P2P. The server part can access simulated disks as well as real disks. There are several strategies can be simulated for video replication. There are varieties algorithms can be simulated for cache replacement. The automatic test module, which has a user friendly interface, can flexibly set up the test parameters and environment, and can easily generate the test instances and collect the results.Many tests are made with the simulator and the results are quite agreement with those of a real VOD experimental system. It is found that, in the simulating tests for the striped HD-VOD system, the size of video strip has a significant impact on the performance of a video server. The optimal range of the size, within which the strip size is appropriate for the striped HD-VOD system, is determined. According to this result, a real HD-VOD experimental system is reconfigured with which the performance is promoted to about20%higher. It is confirmed that, in the simulating tests for maliciously replaying videos to disturb the HD-VOD systems, the striped HD-VOD system exhibits excellent capability to resist the dry scratching. |
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