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I'm surprised that (it seems) google isn't using Multipath TCP to carry the VPN traffic to google. This would allow it to switch seamlessly between LTE and Wifi and in theory even LTE and LTE while maintaining the VPN connection and thus the call.

In fact, Apple uses this tech for Siri to reduce latency on voice queries.

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(author here) I didn't have a chance to test how the VPN works, but even if they were using MPTCP the switch wouldn't necessarily be seamless.

Especially how they are using it now - which hands over a Wi-Fi call (which is data) - to a cellular voice call (not data). It's a subtle point, but calls over cellular are not data, so they are not using TCP/UDP/MPTCP/etc.

> but calls over cellular are not data

Does this change with VoLTE?

https://en.wikipedia.org/wiki/VoLTE

Yes - with VoLTE, calls are also data.

I see, for some reason I thought it was Voice over IP tunnelled to google via VPN (over wifi or LTE). My mistake.

Exactly. They are doing VoIP over Wi-Fi (VoWiFi), but not VoIP over 3G/LTE (which is VoLTE if you follow certain standards).

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