You are building a hotel with 100 rooms. Each room is to have a video?on?demand television that displays movies in HDTV resolution of 1920 × 1080 pixels at 30 frames/s. If each pixel is 24 bits and you can compress video data by a factor of 100, determine the following.
a. What is the maximum bit rate that can be demanded if you assume that, in the worst case, 70% of the
rooms will be watching television?
b. What is the required disk storage capacity if the hotel provides 250 movies on demand, each lasting on
average 90 minutes?
c. When a viewer selects a new movie, the server is interrupted and an appropriate routine is executed. The
switching routine is composed of approximately 15,000 instructions that take approximately one
cycle/instruction on a processor running at 4 GHz. If a user can cope with a latency of 80 ms (i.e., a delay in
the data stream of less than 80 ms is not visually disturbing), how many simultaneous switch?overs can the
system handle at any instant?
a. 100 rooms × 1920 × 1080 × 30 frames × 24 bits/100 compression rate = 1,492,992,000 bits/s = 1.5 Gbits/s.
If 70% represents the worst case viewing factor, the maximum rate is 0.7 × 1.5 = 1.05 Gb/s.
b. Assuming the same compression ratio, a 90 minute movie would require 1920 × 1080 × 30 × 24 × 90 min ×
60s / 100 (compression) / 8 (bits to bytes) = 10,077,696,000 = 10.1 GB per disk , or 2.519 TB for the library.
c. Time to switch channels is 15,000 instructions at 4 GHz = 15,000 × 0.25ns = 3,750 ns = 3.75 ms. If 80 ms is
the maximum delay that can be tolerated, then 80/3.75 = 21 simultaneous changeovers.
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