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Broadcast Scheduling. Push mode Server continuously pushes information in broadcast channel Clients access information by tuning in and waiting until information of interest is transmitted Server follows schedule (program) Attempts to match users access statistics to reduce access latency
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Broadcast Scheduling • Push mode • Server continuously pushes information in broadcast channel • Clients access information by tuning in and waiting until information of interest is transmitted • Server follows schedule (program) • Attempts to match users access statistics to reduce access latency • Challenge: algorithm for constructing the optimal schedule that minimizes average access time
Pull mode • Clients submit requests • From outstanding requests server determines which data object to broadcast next • Challenge: Pick object that greatly improves effectiveness • In the remainder we will focus on push mode
Push-based Broadcast: Model I • Server • Constructs broadcast program is not aware of clients‘ requests (push), and hence only takes into account the distribution of requests • N data objects • Broadcast consist of broadcast cycle of size L time units • Object may appear more than once in a broadcast cycle • Frequency : number of copies in a broadcast cycle
Server Broadcast Programs Generating a multi-disk broadcast • Number of disks (num_disks) determine the number of different frequencies with which pages will be broadcast. • For each disk, the number of pages and the relative frequency of broadcast (rel_freq(i)) are specified.