Find how many VoWiFi calls an access point can carry from its PHY rate and airtime efficiency, and how many APs a site needs.
Wi-Fi is a shared half-duplex medium, so uplink and downlink audio both consume airtime from the same budget. Voice frames are small and mostly overhead, which is why usable throughput for VoWiFi sits near 40% of the nominal PHY rate, and the ePDG IPsec tunnel adds a further per-packet cost. Access points typically fall over at 20–30 concurrent calls long before their throughput figure suggests, so airtime — not megabits — is the number that decides AP density.
VoWiFi Capacity
calls per AP = (PHY rate × airtime efficiency) ÷ (per-call bandwidth × 2 directions), with the per-call rate inflated by IPsec overhead.
calls per AP = (PHY rate × airtime efficiency) ÷ (per-call bandwidth × 2 directions), with the per-call rate inflated by IPsec overhead. Wi-Fi is a shared half-duplex medium, so uplink and downlink audio both consume airtime from the same budget. Voice frames are small and mostly overhead, which is why usable throughput for VoWiFi sits near 40% of the nominal PHY rate, and the ePDG IPsec tunnel adds a further per-packet cost.
Access points typically fall over at 20–30 concurrent calls long before their throughput figure suggests, so airtime — not megabits — is the number that decides AP density.
This calculator takes 5 inputs: Usable PHY rate at the cell edge, Airtime efficiency for small voice frames, Bandwidth per call on the wire, Concurrent calls the site must carry, IPsec/ePDG tunnel overhead. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.