Why is WiFi Calling dropping ass-loads of calls?
Or more accurately: *Why are my text messages failing to send, and some inbound calls dropping within 10 seconds of answering when using T-Mobile's WiFi Calling, and an iPhone Six Plus?
Short Answer
AiRadar (Asus) and/or beamforming (Netgear and everyone else) is breaking your iPhone's wifi-SMSs and wifi-calls.
Long Answer
I have an Asus rt-ac66u. Last week I was tinkering around and upgraded from the latest stable asus firmware to the latest beta asus firmware (3.0.0.4.378.9533, and 9.0.0.4.380.2695 respectively.) From that point forward, practically every inbound call (but pretty much zero outbound) and virtually all sms traffic over T-Mobile WiFi quit working.
Turns out that AiRadar, also known as beamforming is enabled by default in the beta firmware. Beamforming and Apple iPhone/iPads don't play well together. Turns out it really screws with your iPhone's networking stack and will cause a bunch of network weirdness including, but not limited to (ta da): wifi calling and wifi sms.
By the time I realized what was happening, I had bricked my router by trying to downgrade to asus' latest stable firmware and kicking it in the middle. Now I'm back on latest stable, sans beamforming, and wifi calls/sms are working perfectly again.
Why just inbound?
This is pure conjecture as I haven't taken any steps to verify this is actually correct.
I'm guessing the beta build uses beamforming for every wifi session unless it detects a failure (aka implicit beamforming), at which point it disables beamforming for the next session to the same device.
I'm also guessing my iPhone sleeps its radios when the screen isn't on, which would cause a new wifi session to come to life between the phone and the router with beamforming.
With those two assumptions, the sequence of events for an inbound call looks like this:
Inbound call causes iPhone wifi radios to wake and re-establish connection with the AP
AP uses beamforming to create the new connection
I answer the call, and then the beamforming connection drops, and subsequently drops the call
The router notices the drop and switches off beamforming to that device for the next session
New session gets established without beamforming, and voila wifi appears to work fine for the rest of the time I'm using my phone.
This also explains why SMSs sent via from my macbook would be broken.
Just a guess though. The 802.11 spec, and the router firmware code would know for sure.
my gear
Asus rt-ac66r (same as the rt-ac66u)
Asus Firmware 9.0.0.4.380.2695 (beta track)
iPhone Six Plus
iOS 9.3.2 (beta track)
T-Mobile WiFi Calling
If you're seeing the same behavior with different gear, feel free to leave a comment detailing what it is so people from google can compare/contrast.
