Erlang for Excel ™ is an Add-In for Microsoft Excel that allows Erlang B and C traffic calculations to be included in any Microsoft Excel worksheet.  The Add-in defines eight Erlang functions that can be added to spreadsheets in the same way as regular functions.

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These functions assist in estimating the number of telecommunications lines required to make up a trunk group; to analyse the performance of an existing trunk group and to estimate the number of call center agents required at an inbound call center.

Erlang for Excel ™ is included free with Westbay Traffic Calculators, which is available for 139 US Dollars.   Click here to find out how to purchase.

This picture shows one of the Erlang B Add-In functions in use.

The right hand column contains the results of calculations using the ErlBLines() function to work out how many lines are required to carry the busy hour traffic in the left hand column.

The eight functions which the Add-In offers are:

• ErlBLines()
• ErlBBlocking()
• ErlBTraffic()
• ErlCAgents()
• ErlCCalls()
• ExtErlBLines() *
• ExtErlBBlocking() *
• ExtErlBTraffic() *

* Extended Erlang B examples have not been included below.  The functions are exactly the same as their Erlang B equivalent, except that they have an additional parameter for the recall factor.

if the busy hour traffic is 100 Erlangs,
and the maximum acceptable blocking is 0.025 (2.5% of calls)

then the following formula will return the number of lines required (111).

=ErlBLines(100,0.025)

This function is used to work out how much blocking would be experienced if the busy hour traffic and number of lines are known.  For example:

if the busy hour traffic is 1500 Erlangs,
and there are 1000 lines,

then the following formula will return the blocking encountered (0.335).

=ErlBBlocking(1500,1000)

This function is used to work out how much traffic a trunk group can handle number of lines within that trunk group are known.  For example:

if the target blocking figure is 0.03 (3% of calls blocked)
and there are 200 lines,

then the following formula will return the busy hour traffic in Erlangs which the trunk group could handle (190.881).

=ErlBTraffic(0.030,200)

This function is used to estimate the number of agents required at an inbound call center for given call volumes.  For example, to answer the following question:

if 3000 calls are received in a call center in one hour, and the average call duration is 300 seconds, how many agents are required if 85% of calls must be answered within 20 seconds?

then the following formula will return the number of agents required (263).

=ErlCAgents(3000,300,85,20)

This function is used to estimate the number of calls a call center can handle for a given number of agents.  For example, to answer the following question:

if 115 agents are available to handle inbound calls, and the average call duration is 250 seconds, how many calls can be handled agents if 80% of calls must be answered within 20 seconds?

then the following formula will return the number of calls that can be handled (1547).

=ErlCCalls(115,250,80,20)

"How many lines do I need in a trunk group if that trunk group is offered 200 Erlangs of traffic during its busy hour and I accept that 1.2% of calls will fail due to blocking?" - Answer 2210

Westbay Traffic Calculators is provided with a fully formatted and illustrated User Guide which is distributed electronically in the form of Web pages. This User Guide explains how to use the calculators and offers many examples of their use. There is also a Windows help system installed with the software.

Westbay Traffic Calculators, which comprises Erlang for Excel and the four calculators described above, costs 139 US Dollars for a single user licence.   You can pay using any major credit card.

Transactions are with Westbay Engineers Ltd. and are handled on our secure server.  You can have the software running on your PC five minutes from now!)

Erlang for Excel supports all Windows versions of Microsoft Excel from Excel 97 onwards and including Excel 2007.