This page was set-up for those needing to perform rough calculations on resource management using Erlang-B and Erlang-C calculations. This worksheet uses the Erlang-B and Erlang-C equations to calculate the appropriate grade of service (GOS). Enter each of the parameters, then press the "Calculate" button at the bottom of each section.

Calculating Erlang-B Blocking Probability

In this section, you need to enter the offered load to the system, which is typically denoted "A", and is measured in erlangs. You also need to enter the number of available channels in the system. For example, you might have a cellular system in which one tower provides 27 channels. If the system is handling 200 calls / hour, and each call lasts 6 minutes, this would correspond to an offered load of (200 calls/hour)*(1 hour/60 minutes)*(6 minutes/call) = 20 erlangs. We could then plug in the value of "20" (for the offered load) into the first box, and the value of 27 (for the number of available channels) into the second box, then press "Calculate Blocking Probability". This would give us an answer of 0.0268. This means that the probability of a channel being blocked for any particular caller would be 0.0268, or 2.68%.

Calculating Erlang-B Offered Load

In this section, you need to enter the desired grade of service (GOS) for the system and the number of available channels (C). The grade of service (GOS) is nothing more than the probability of a call being blocked for a given offered load as well as the number of available channels. This script will calculate the offered load which provides the grade of service, given the number of available channels. For example, you might have a cellular system in which one tower provides 43 channels. If the desired grade of service is 0.02, we could then plug in the value of "0.02" (for the grade of service) into the first box, and the value of 43 (for the number of available channels) into the second box, then press "Calculate Offered Load". This would give us an answer of 33.758. This means that a system with 43 channels wishing to provide a 0.02 grade of service (or 2% blocking probability) would be able to handle 33.758 erlangs of offered load. If the offered load increases beyond this, then the grade of service, meaning the blocking probability, would rapidly increase.

Calculating Erlang-C Delay Probability

This section calculates the probability that a call will be delayed before it is serviced. This is Pr(Delay>0). You need to enter the amount of offered load to the system, in erlangs, as well as the number of available channels. This script will then calculate the probability of a delay occurring given these two parameters. For example, consider a system with an offered load of 15 erlangs and with 25 available channels. Plug in "15" (the offered load) into the first box and "25" (the number of available channels) into the second box. Then press "Calculate Delay Probability". This would provide a probability that the delay is greater than 0 of 0.01243.

Calculating Erlang-C Offered Load

This section calculates the offered load that can handle, given a grade of service (the probability that a call will be delayed) and an available number of channels. For example, consider a system with a grade of service (probability of delay) of 0.035 and 37 available channels. Plug in "0.035" (the grade of service) into the first box and "37" (the number of available channels) into the second box. Then press "Calculate Offered Load for Delay". This would provide an offered load of 26.437929 erlangs. This means that the system, with 37 available channels, can handle up to 26.437929 erlangs of traffic before the probability of a delay occuring rises above 0.035.