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Home » Glossary » Erlang Models

Erlang Models


What is an erlang model?

The erlang model is helpful in telecommunications traffic modeling. It can predict the necessary number of employees based on the expected workload for incoming calls and other factors.

Agner Krarup Erlang was a Danish mathematician and was the first to establish telephone network analysis and switchboard staffing. His groundbreaking work in Denmark in the 1920s led to the development of the Erlang Formula.

What is an erlang model

Benefits of using erlang models

Erlang is a general-purpose functional language aimed at creating scalable, concurrent systems with excellent reliability assurance.


Erlang handles the majority of faults not caused by severe implementation flaws.


You can scale systems using Erlang processes by adding new machines or adding more cores to existing ones.


Erlang makes it easier to develop concurrent programs because of this and the language’s functional character.

Three significant erlang models

While Erlang A is greatly useful in predicting the number of abandoned calls in a call center.

The Erlang C and Erlang B models are well-known in telephone call centers because they allow for estimating workforce demand for inbound and outbound calls.

These techniques are limited in real-world call centers since they do not account for call abandonment. 

Erlang A

In 1946, Swedish mathematician Conny Palm adapted the Erlang C formula known as the Erlang A formula. The A in Erlang A stands for Abandons.

Erlang A is used to calculate the expected number of calls abandoned based on high call traffic, caller patience, and the number of employees available.

Erlang B

If you know the expected traffic, you may use it to determine how many lines you need in your trunk groups.

You can also use the formula to calculate any of the following three factors:

  • BHT (Busy Hour Traffic). The number of hours of phone volume at the peak period of the business
  • Blocking. The number of calls dropped due to a lack of accessible lines
  • Lines. A trunk group’s total number of lines

Erlang B can calculate the number of lines required to handle a one-hour calling load. Its extended calculation factors callers who instantly retry when their calls do not go through.

Erlang C 

Erlang C is a traffic modeling approach that is usable for call center planning to determine caller wait times and predict delays.

The Erlang C formula, based on the Erlang B formula, is used in the contact center to determine how many advisers must meet a specific service level. It is a formula that is still widely used in business today.

Erlang C is a traffic modeling technique used in call center scheduling to compute delays or estimate caller wait times. Erlang C’s formula is based on three variables: the number of agents providing service, the number of callers waiting, and the average time it takes to serve each caller.

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