Erlang calculations are used to size contact center resources. Which two resources are sized by using Erlang-B? (Choose two.)

Question

Options

• Areporting ports
• Bestimated wait times
• CPSTN gateway trunks
• Dagents
• EIVR ports

• B
  5% (1)
• C
  90% (19)
• D
  5% (1)

Explanation

Erlang-B models scenarios where blocked calls are lost (no queuing) - making it ideal for sizing fixed-capacity resources like PSTN gateway trunks (C) and IVR ports (E), where an incoming call is simply rejected if all ports/trunks are busy.

Why the distractors are wrong:

• D (Agents) and B (Estimated wait times) use Erlang-C, which models callers waiting in queue - the agent staffing model assumes callers hold for the next available agent, not that they're immediately lost.
• A (Reporting ports) is not a standard Erlang-based calculation at all; report server capacity is sized by different methods.

Memory tip: Think B for Blocked - Erlang-B is for resources where a busy signal means the call is Blocked and dropped (trunks, IVR ports). Erlang-C is for resources where callers Continue waiting (agents, queue sizing).

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