Starting from a time point, no intra-office user (register to SIP server normally) can make calls, including intra-office and outgoing calls. The reason can be ().

Question

Options

• AThe bill pool is full.
• BThe SCU board is faulty and physical channels are disconnected.
• CThe MTU board is faulty.
• DU1900 is disconnected.

• A
  78% (29)
• B
  3% (1)
• C
  14% (5)
• D
  5% (2)

Explanation

Option A is correct because a full bill pool (billing resource pool) triggers a system-wide call block as a policy enforcement mechanism - even though SIP registration succeeds (registration and billing are separate processes). Once the pool is exhausted, the system denies all new call setups for every user, regardless of whether the destination is internal or external.

Why the distractors are wrong:

• B (SCU board faulty): A faulty SCU affects physical/PSTN channels, which would disrupt external calls or analog lines - but intra-office IP calls over SIP would still work. It also would not cause a clean "all users can't call" scenario starting at a single time point.
• C (MTU board faulty): The MTU handles media/trunk connections; a fault here typically disrupts specific trunk groups or media paths, not all intra-office and outgoing calls simultaneously for every registered user.
• D (U1900 disconnected): If the U1900 gateway itself were disconnected, users would fail registration, not just fail calls - but the scenario explicitly states users register normally.

Memory tip: The clue is the two-part symptom - "registered OK" + "all calls blocked." Registration working rules out hardware/connectivity failures (B, C, D). "All calls blocked starting at a point in time" screams a quota/policy trigger, which is exactly what a full bill pool does.

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