Which of the following statements describe the operation of WRED on the Alcatel-Lucent 7750 SR? (Choose three)

Question

Options

• AWRED monitors the shared buffer space utilization over a period of time.
• BWRED disables the TCP slow-start congestion control mechanism.
• CWRED uses two configurable slopes for each buffer pool: a high slope and a low slope.
• DWRED uses the shared buffer utilization, instead of the individual queue depth, to get a better
• EWRED polices the shared buffer pool and marks all packets above a certain rate as "discard

• A
  3% (1)
• B
  3% (1)
• C
  13% (4)
• D
  75% (24)
• E
  6% (2)

Explanation

Note: This question asks for three correct answers, but only D is listed in the provided answer key - likely a formatting issue. Based on 7750 SR WRED behavior, the full correct set is typically A, C, and D. Here's the explanation:

Why D is correct: On the Alcatel-Lucent 7750 SR, WRED makes drop decisions based on the shared buffer pool utilization rather than any individual queue's depth - this gives a global, system-wide view of congestion and produces fairer, more accurate early dropping decisions across all queues sharing that pool.

Why A is likely also correct: WRED does monitor shared buffer space utilization, though the phrase "over a period of time" can be misleading since it typically uses near-instantaneous readings; this wording might make it a trap option.

Why C is likely also correct: The 7750 SR implements WRED via slope policies with a high slope (for out-of-profile/low-priority traffic) and a low slope (for in-profile/high-priority traffic) - this dual-slope design is a key 7750 SR WRED characteristic.

Why B is wrong: WRED does the opposite - it works with TCP's congestion control by triggering early drops so TCP initiates slow-start before buffers overflow, not by disabling it.

Why E is wrong: That describes policing, not WRED. WRED randomly drops packets with increasing probability as buffers fill; it doesn't hard-drop everything above a threshold.

Memory tip: Think of WRED as a shared pool lifeguard - it watches the whole pool (shared buffer), has two alarm levels (high/low slopes), and nudges TCP swimmers to slow down early rather than waiting for a full-pool crisis.

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