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

Question

Options

• Aagents
• BIVR ports
• CPSTN gateway trunks
• Dreporting ports

• A
  8% (2)
• B
  81% (21)
• D
  12% (3)

Explanation

Erlang-B models scenarios where blocked calls are lost (cleared) rather than queued - making it ideal for sizing finite port/trunk resources that simply reject overflow traffic. IVR ports (B) and PSTN gateway trunks (C) both fit this model: when all ports or trunks are occupied, an arriving call is rejected outright and does not wait.

Why the distractors are wrong:

• A (agents): Agents are sized using Erlang-C, which models queued (delayed) calls - callers wait on hold rather than being dropped, so the "blocked calls cleared" assumption doesn't apply.
• D (reporting ports): Reporting ports are not typically sized using Erlang formulas at all; they are provisioned based on concurrent user estimates, not traffic intensity models.

Memory tip: Think of Erlang-B as "Busy = Bye" - if the resource (trunk or IVR port) is full, the call leaves immediately. Erlang-C is for "Call waits in a Cue" - which is what happens when you're waiting for an agent.

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