Referring to the exhibit, which oversubscription ratio applies to Switch-3?

Question

Exhibit

Options

• A2:4
• B4:1
• C2:1
• D1:2

• A
  4% (2)
• B
  75% (42)
• C
  14% (8)
• D
  7% (4)

Explanation

Option B (4:1) is correct because oversubscription ratio is calculated as total downlink (access) bandwidth ÷ total uplink bandwidth. Based on the exhibit, Switch-3's downlink capacity is four times greater than its uplink capacity, meaning up to four times more traffic could theoretically be generated than the uplinks can carry simultaneously - a standard access-layer design tradeoff.

Why the distractors are wrong:

• A (2:4) simplifies to 1:2, which would actually mean the uplinks outpace the downlinks - the opposite of oversubscription.
• C (2:1) describes a lower oversubscription (only 2x), which doesn't match Switch-3's port/uplink configuration in the exhibit.
• D (1:2) is the same as A's simplified form - more uplink than downlink bandwidth, meaning no oversubscription exists at all.

Memory tip: Think of oversubscription as "how many ports are fighting over each uplink lane." The ratio is always downlinks : uplinks, so a bigger first number means more contention. If you see 4:1, four units of traffic compete for one unit of uplink - that's oversubscribed. Flip it (1:4 or 1:2) and you have surplus uplink capacity, which is undersubscribed.

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