Troubleshooting Wi-Fi Calling (VoWiFi) Issues with Zyxel Access Points

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If you are experiencing issues with Wi-Fi Calling (VoWiFi) when using Zyxel Access Points, it's important to understand how Zyxel APs handle this traffic and what common troubleshooting steps can resolve the problem.

1. Define "WLAN Telephony": First, clarify what type of "WLAN telephony" you are experiencing issues with. Are you referring specifically to Wi-Fi Calling (VoWiFi) on mobile devices or other types of voice communication over WLAN (e.g., SIP phones, softphones)?
2. Scope of the Issue: Determine if the problem affects all end devices or only specific client stations (STAs).
3. Zyxel APs and VoWiFi Traffic: Zyxel Access Points are designed to transparently forward data traffic and do not actively block VoWiFi-relevant protocols, such as UDP ports 500 and 4500 (used for IPSec/IKE).
4. Check Upstream Devices: If problems persist, investigate whether an upstream router or an ISP device might be filtering or restricting VoWiFi data traffic.
5. Required Ports for VoWiFi: For more information on the necessary ports for VoWiFi, refer to the relevant Zyxel documentation, such as the article: FLEX/ATP – Which service ports must be opened for VoWiFi?