Week 8

This week research is about Erlang. Erlang is a general-purpose concurrent programming language and runtime system. The sequential subset of Erlang is a functional language, with strict evaluation, single assignment, and dynamic typing. While threads are considered a complicated and error-prone topic in most languages, Erlang provides language-level features for creating and managing processes with the aim of simplifying concurrent programming. Though all concurrency is explicit in Erlang, processes communicate using message passing instead of shared variables, which removes the need for locks.

An Erlang is a unit of telecommunications traffic measurement. Strictly speaking, an Erlang represents the continuous use of one voice path. In practice, it is used to describe the total traffic volume of one hour.

Erlang B is a modeling formula that is widely used in call center scheduling. The formula can be used to calculate any one of the following three factors if you know or predict the other two:

• Busy Hour Traffic (BHT): the number of hours of call traffic during the busiest hour of operation

• Blocking: the percentage of calls that are blocked because not enough lines are available

• Lines: the number of lines in a trunk group.

Erlang B can determine the number of trunks, or lines, needed to handle a calling load during a one-hour period. However, the formula assumes that lost calls are cleared; i.e., if callers get a busy signal, they will never retry. This assumption means that Erlang B can underestimate the number of trunks needed. For this reason, it is best used in situations with few busy signals. The Erlang B Extended formula takes into account the callers who will immediately retry if their calls do not go through.

Formula for Erlang B

Erlang C is a traffic modeling formula used in call center scheduling to calculate delays or predict waiting times for callers. Erlang C bases its formula on three factors: the number of reps providing service; the number of callers waiting; and the average amount of time it takes to serve each caller. Erlang C can also calculate the resources that will be needed to keep wait times within the call center's target limits. This method assumes that there are no lost calls or busy signals, and therefore may overestimate the staff that is required.

Because Erlang B is so simple to use (insert two numbers, it calculates the third), many managers assume that Erlang C will be similarly easy. That’s a mistake — even basic Erlang C calculations are difficult, and more complex ones can be daunting indeed. Erlang C is most commonly used to calculate how long callers will have to wait before being connected to a human in a call centre or similar situation. This adds complexity in at least four areas.

Formula for Erlang C