# What are Erlang calculators?

Erlang calculators are an essential part of any telecom planner’s toolkit. In this article, we explain what they do , how they came about and where to find them.

## Answering the most basic question

With technology developing at break-neck speed, telecoms engineers are faced with a huge variety of challenges daily, but the most basic question has never changed: how many lines do I need? Lines (or circuits or voice paths) connect our equipment. These days, they may not be made of copper – they may not even be physical connections – but interconnection is what telecom specialists do best. To answer this question quickly and confidently, you’ll need an Erlang calculator.

Examples of interconnections might be:

• Central office exchange lines
• Virtual circuits within a VoIP infrastructure
• Connections to a standalone voicemail system
• Teleconferencing facilities
• Direct lines between buildings

## Before Erlang calculators

It’s hard to imagine, but there was a time when every desk didn’t have a computer on it. When faced with deciding how many lines an engineer needed, they would lug out their Erlang B tables, heavy tomes with hundreds of dog-eared pages. Here’s a page from my own book that I used in the 1990s:

From my scrawling, it looks like I wanted to work out how many Erlangs of traffic a group of 90 lines could be offered if I accepted a blocking figure of 0.3%.

## Enter computers

Life is easier now. To make the same calculation, I now use an Erlang calculator that sits on my desktop computer. Erlang calculators offer instant answers and scale up to tens of thousands of lines.

This app, Westbay Traffic Calculators, lets you set any of the three parameters (traffic, blocking or lines) as the unknown value to be calculated and includes three other modules for Extended Erlang B, Erlang C and Call Minutes. Printed Erlang tables are now museum pieces.

A good tool is one you can forget about – it’s always there and never fails. When our customers upgrade their computers, they often forget about their reliable Erlang calculators until the next time they need them. They contact us, desperate for a reinstallation to help them with their latest project. No problem: all our products come with free upgrades for life with a once-only licence fee. We’re trusted by the world’s greatest companies.

## Online Erlang calculators

You’ll also find web-based calculators. Our company published the world’s first online Erlang calculators in 1996. They’re not as powerful and scalable as our Windows version, but they’re free and offer an excellent introduction to traffic engineering for the newcomer.

## Erlang in Excel

For more complex network planning, you’ll find it useful to perform Erlang calculations in speadsheets. Erlang for Excel, introducing eight Erlang functions into Excel for use in your own workbooks. With some knowledge of Excel, you can use its more advanced features such as lookup tables, conditional formatting and charting to build detailed modelling tools.