Westbay Traffic Calculators FAQ

Here is a list of questions we are commonly asked about Westbay Traffic Calculators. Please contact us if you have any others.

How is Erlang B used for trunk dimensioning?

Erlang B is a traffic model which can be used to explore the relationship between the busy hour traffic offered to a trunk group, the required grade of service and the number of lines required. That makes it useful for route dimensioning (determining how many lines are required on a trunk group).

How can I work out how many lines I need?

The Erlang B traffic model included with Westbay Traffic Calculators can help you work out how many lines you should install in a trunk group. You can learn the process of sizing a trunk group in our technical paper.

How many call center agents do I need?

You can use the Erlang C traffic model included with Westbay Traffic Calculators to estimate how many agents you need at your inbound call center. We explain the process of call center agents calculation in our technical paper.

Should I include wrap-up time with Erlang C?

Yes. Wrap up time (or wrap time) is the time your agent remains unavailable after finishing with a call, usually to complete call-related administrative tasks. As wrap up time uses an agent’s time in the same way as actually handling a call, it should be included in the average call duration figure.

However, when using Erlang B to estimate the number of lines required into a call center to deliver inbound calls, wrap up time should not be included, but the average delay to all calls should be included as queuing time occupies a trunk in the same way as conversation time.

How do I work out the Busy Hour Traffic?

You need to work out the number of hours traffic offered to a trunk group during the busiest hour. Use the following formula:

Busy Hour Traffic = Number of calls * Average call duration (s) / 3600

If possible, you should extract these figures from a call logger. Otherwise, you will need to make reasonable estimates based on your understanding of your business. Remember that the busy hour figure should represent the busiest hour you are ever likely to encounter, so use a month or two’s data to work it out.

Does Westbay Traffic Calculators have reporting capabilities?

Yes. By pressing the Results button, you can see a list of all calculations you have made during the previous week. You can filter this list so that the results on view are only for the current session, or any day during the past week. This calculation history can also be printed.

Does Westbay Traffic Calculators include the Poisson traffic model.

We don’t think it’s very accurate, so we do not support Poisson (or Molina). To model situations where there are a high number of retries (callers who immediately redial because they have encountered blocking) we prefer to use the Extended Erlang B traffic model because it allows you to specify the ratio of blocked calls that will immediately retry.

What are Westbay Traffic Calculator’s operational limits?

The Erlang B calculator works up to 90,000 lines and 90,000 Erlangs busy hour traffic. The Erlang C calculator works up to 30,000 calls per hour and 10,000 agents.

What versions of Windows does Westbay Traffic Calculators run on?

Our desktop products work on all versions of Windows from Vista to Windows 10. We do not make software for the Apple Mac.

How much does Westbay Traffic Calculators cost?

Westbay Traffic Calculator (including Erlang for Excel) costs $69 (US Dollars) for an installation on a single computer. We also offer licences for single buildings and global use.

This is a once-only payment and includes free upgrades for the lifetime of the product.

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2 Replies to “Westbay Traffic Calculators FAQ”

    1. This was a known problem and was fixed in a release in August 2018. I have written to you by email with downloading instructions for the latest version. Please reply if you need any further support.

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