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Call Centre Example

Dr Angela Moore created a Call Centre Simulator as a university project. We still use this software today when working with call centres, as it gives an in-depth look at what happens to calls during changes to operations or call volumes. This is unique software which will tell you not only what will happen but explain why.

In this example we will use a period of flat call rate (the call rate will remain static for the period), and have an incoming call rate of 100 call per half hour. The average length of call is 180 seconds (3 minutes). In this example we will have 10 operators to answer the calls. There will be no initial call delay and no calls will be prematurely terminated (no one will hang up because they are not answered).

So we enter these parameters.


The result is that the average call delay would be 0.3 seconds per call. Even at the end of an hour the last call was answered in 5.5 seconds.

The graph below shows how the calls are delayed. Most calls were answered with no delay.


Everything is going fine, so an operator would like a toilet break, how long can they have?

This can be simulated.

First we reduce the number of operators by one; therefore nine operators are available to answer calls. Over an hour the average call delay rises to 162.4 seconds and the last call is waiting 321.3 seconds to be answered, over five minutes.


The graph below shows the call delay ramping up. After just half an hour the delay is over 200 seconds.


Unanswered calls soon start to build up and if the call delay time is set to one minute as a maximum, this happens after about 40 calls. The results show that about 4 calls are waiting in the queue. See the graph below.


Often a call centre needs to find out how quickly a bad situation can occur. The above graph shows that almost instantly the delay starts increasing rapidly. An innocuous action can create serious difficulties and often does. The call centre tempo suddenly changes due to very simple causes, and it is often difficult to know where these causes originated.

This information shows that a 10-12 minute toilet break will generate a queue and a waiting time, very quickly.

Now the program can be run again with the operator returning to duty after 10 minutes, with a queuing time of 60 seconds and 4 people in the queue. See the input parameters below.


The graph below shows that it takes 140 calls to return to the situation prior to the operator’s 10-minute toilet break. At 100 calls/half hour, this is 40-45 minutes. Or in practical terms, the operators can only have toilet breaks at intervals of 55 minutes, so for 10 operators that is once per day!


A common problem for call centres is understanding why, when they have enough staff, the call delay time does not stay at a few seconds.

From this example the answer is obvious: they forgot to allow for breaks.