Erlang Traffic Intensity
Offered call traffic from call rate and average holding time.
Formula
Variables
Example
λ=120/hr, h=3 min=0.05 hr: A = 6 Erlangs
How it works
Erlang traffic intensity measures how much total call time is being offered to a communication system. It is found by multiplying how often calls arrive, λ, by how long each call stays active, h, because traffic is essentially "call opportunities per unit time" times "time occupied per call." The result, A, is the average number of simultaneous calls the system would need to carry if the arrivals and durations stayed steady.
When to use it
Use this when sizing or analysing telephone exchanges, call centers, VoIP trunks, radio channels, or any system where many sessions arrive and occupy resources for a period of time. It helps estimate load before applying blocking, queuing, or capacity formulas.
Worked example, step by step
Suppose a call center receives λ = 75 calls per hour and the average call duration is h = 4 minutes. Convert the holding time to hours: h = 4/60 = 0.0667 hr Apply the formula: A = λh A = 75 × 0.0667 A = 5.0 Erlangs Final answer: the offered traffic intensity is 5 Erlangs.
Common mistakes to avoid
- Using minutes for h while λ is in calls per hour, which gives inconsistent units
- Confusing traffic intensity with the number of calls arriving in a time period
- Treating Erlangs as a count of calls instead of average occupied capacity
Did You Know?
One Erlang equals a single circuit kept busy continuously — the unit is named after Danish engineer A. K. Erlang.
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