Calculator Inputs
Choose a mode, enter telecom traffic data, and calculate blocking probability, required channels, or maximum traffic for a target grade of service.
Example Data Table
These example cases show how blocking changes as offered traffic and channel count shift in a loss system.
| Scenario | Offered Traffic (Erlangs) | Channels | Blocking Probability (%) | Carried Traffic (Erlangs) |
|---|---|---|---|---|
| Case 1 | 8.00 | 10 | 12.1661 | 7.0267 |
| Case 2 | 10.00 | 12 | 11.9739 | 8.8026 |
| Case 3 | 12.50 | 15 | 10.0489 | 11.2439 |
| Case 4 | 15.00 | 18 | 8.6169 | 13.7075 |
| Case 5 | 18.00 | 22 | 6.5451 | 16.8219 |
Formula Used
1) Offered traffic: A = λ × h
When call attempts are entered per hour, convert holding time to hours first. For seconds, use A = λ × h / 3600. For minutes, use A = λ × h / 60.
2) Erlang B loss formula:
B(N, A) = (A × B(N-1, A)) / (N + A × B(N-1, A)), with B(0, A) = 1
This recursive form is stable and efficient for telecom traffic engineering. It estimates the probability that a new call is blocked when all channels are occupied.
3) Carried traffic: Ac = A × (1 - B)
4) Lost traffic: Al = A × B
5) Average channel utilization: Utilization = (Ac / N) × 100%
How to Use This Calculator
- Select the calculation mode based on your engineering goal.
- Choose whether to enter traffic directly or derive it from call attempts and holding time.
- Enter the known values such as channels or target blocking probability.
- Press Calculate Now to display results above the form.
- Review blocking, service probability, carried traffic, lost traffic, and utilization.
- Use the chart to compare how blocking changes as channel count increases.
- Download the result summary as CSV or PDF for reports.
FAQs
1) What does call blocking probability mean?
It is the chance that a new incoming call finds every channel busy and cannot be served immediately. Lower values mean better service availability and less congestion.
2) When should I use the Erlang B model?
Use Erlang B for loss systems where blocked calls are cleared and do not wait in a queue. It is common in telecom trunk sizing and radio channel planning.
3) What is offered traffic in Erlangs?
One Erlang represents one continuously occupied channel. Offered traffic combines arrival rate and average holding time to describe total demand placed on the system.
4) Why does blocking decrease when channels increase?
More channels raise available capacity, so simultaneous calls are less likely to exhaust resources. That reduces the probability of new calls being denied service.
5) What blocking target is usually acceptable?
Many voice systems target about 1% to 2% blocking during busy hour conditions, but acceptable limits vary by service level, regulation, technology, and customer expectations.
6) Can I calculate traffic from calls and holding time?
Yes. This calculator can derive traffic from call attempts per hour and average holding time in seconds, minutes, or hours before applying the Erlang B model.
7) What is carried traffic?
Carried traffic is the portion of offered demand that the system actually serves. It equals offered traffic multiplied by the probability of successful service.
8) Why is utilization useful alongside blocking probability?
Utilization helps show how efficiently channel capacity is used. A design can have low blocking with excess spare capacity or acceptable blocking with tighter utilization.