group-guaranteed channel capacity in multimedia storage servers
One of the open questions in the design of multimedia storage servers is in what order to serve incoming requests. Given the capability provided by the disk layout and scheduling algorithms to serve multiple streams simultaneously, improved request scheduling algorithms can reduce customer waiting times. This results in better service and/or lower customer loss. In this paper we define a new class of request scheduling algorithms, called Group-Guaranteed Server Capacity (GGSC), that preassign server channel capacity to groups of objects. We also define a particular formal method for computing the assigned capacities to achieve a given performance objective. We observe that the FCFS policy can provide the precise time of service to incoming customer requests. Under this assumption, we compare the performance of one of the new GGSC algorithms, GGSC W -FCFS, against FCFS and against two other recently proposed scheduling algorithms: Maximum Factored Queue length (MFQ), and the FCFS-n algorithm that preassigns capacity only to each of the n most popular objects. The algorithms are compared for both competitive market and captured audience environments.Key findings of the algorithm comparisons are that: (1) FCFS-n has no advantage over FCFS if FCFS gives time of service guarantees to arriving customers, (2) FCFS and GGSC W -FCFS are superior to MFQ for both competitive and captive audience environments, (3) for competitive servers that are configured for customer loss less than 10\%, FCFS is superior to all other algorithms examined in this paper, and (4) for captive audience environments that have objects with variable playback length, GGSC W -FCFS is the most promising of the policies considered in this paper. The conclusions for FCFS-n and MFQ differ from previous work because we focus on competitive environments with customer loss under 10\%, we assume FCFS can provide time of service guarantees to all arriving customers, and we consider the distribution of customer waiting time as well as the average waiting time.
group capacities multimedia timing storage server design order layout scheduling algorithm algorithm custom paper class object formal methods computation performance policy precise competition environments variability distributed