A queue is configured with the following attributes: MBS = 10KB CBS = 5KB High-Priority-Only = 20% Assume that there is no CBS overbooking and that the slope-policy is disabled. If the current queue…

Question

Options

• AIt will be queued in the reserved portion of the buffer pool and remain out-of-profile.
• BIt will be queued in the reserved portion of the buffer pool if there are no in-profile packets already
• CIt will be queued in the reserved portion of the buffer pool and be in-profile.
• DIt will be queued in the shared portion of the buffer pool but contend for shared buffer space with
• EIt will be queued in the shared portion of the buffer pool but may be dropped if the buffer

• A
  46% (29)
• B
  3% (2)
• C
  14% (9)
• D
  29% (18)
• E
  8% (5)

Explanation

Option A is correct because the current queue depth (3KB) is below the CBS threshold (5KB), meaning the arriving packet - regardless of its profile - gets placed in the reserved portion of the buffer pool. However, a packet's profile marking is determined by upstream metering/policing, not by which buffer region it occupies, so the packet remains out-of-profile even though it landed in reserved space.

Why the distractors fail:

• B is wrong because access to reserved buffer space (below CBS) is not conditional on whether in-profile packets are already there - both profile types can use it when queue depth < CBS.
• C is wrong because buffer location never promotes a packet's profile; out-of-profile stays out-of-profile regardless of where it's buffered.
• D & E are wrong because shared buffer space only comes into play once queue depth exceeds CBS (5KB); at 3KB, there's still reserved space available, so the shared pool is irrelevant here.

Memory tip: Think of CBS as a "personal parking spot" - if your spot isn't full yet, any car (in- or out-of-profile) can park there, but a budget rental car (out-of-profile) doesn't become a luxury car just because it parked in a reserved space.

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