ITPEC FE Morning April 2022 Question 32
There exists a system that connects a head office to a factory via a leased line and sends form data. The size of each form is 2,000 bytes, and header data totaling 400 bytes is attached to every two (2) forms to be sent through this system. On average, 100,000 forms per hour are generated. When the line speed is 1 Mbit/s, what is the line’s utilization rate in percentage?
Explanation
49% — the data actually sent per second, headers included, divided by the line speed.
- •Header per form: 400 ÷ 2 = 200 bytes, so each form sends 2,000 + 200 = 2,200 bytes
- •Per hour: 100,000 × 2,200 = 220,000,000 bytes, or 220,000,000 × 8 = 1,760,000,000 bits
- •Per second: 1,760,000,000 ÷ 3,600 ≈ 488,889 bit/s
- •Utilization: 488,889 ÷ 1,000,000 ≈ 0.489, about 49%
Answer (c)
Why not others:
- •(a) 6.1 — skips the conversion to bits: 61,111 bytes per second divided by 1,000,000 bit/s mixes bytes with bits.
- •(b) 44 — leaves the header out: 100,000 × 2,000 × 8 ÷ 3,600 ≈ 444,444 bit/s.
- •(d) 53 — attaches 400 bytes to every form instead of every two: 2,400 bytes per form gives about 533,333 bit/s.
Key rule: Line utilization is the bits actually sent per second divided by the line speed; include overhead in its true proportion and convert bytes to bits.
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