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Network handover in Google Fi

nicholasarmstrong.com

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Re: Network handover in Google Fi

#21

Post by tyingq »

jewel wrote: post #4

When Fi was announced they mentioned that public wifi traffic would go through a VPN to google's datacenters. At the time I assumed that they'd just run ALL traffic through the VPN, since that'd make for some very seamless switching. As bad as that would be from a privacy perspective, I trust Google more than T-Mobile or Sprint. By running everything through the VPN, you'd be able to have TCP connections that didn't…

"from a privacy perspective, I trust Google more than T-Mobile or Sprint"

From a privacy perspective, I would not trust an advertising company (Google) more than a telecom. Google is perhaps better about disclosure to a Government entity, but they would be worse about exploiting your data for their own ends.

Re: Network handover in Google Fi

#22

Post by a-dub »

"Given that two different profiles exist on the Fi SIM, the Fi software must have the capability to switch between them. SIM cards are actually little computers, so by developing an application that runs on the SIM card Google could trigger a switch based on any of the information the SIM has access to – the network it is registered on, the receipt of a trigger SMS, or something else.

My guess is that the SIM card contains a small application that can activate a specific profile in response to a command from the Fi software. This profile then remains active until another such command is received. Logically, this makes sense – the algorithms Google will want to use as part of the system are much easier coded as part of an app that can be updated through the Play Store and access any number of data sources; once it decides, it simply instructs the SIM to activate the desired profile."

More likely is that the SIM card just holds a few different profiles and custom software that runs on the baseband processor watches the strength of both networks and sends out of band messages back home to tell recycled Google Voice infrastructure how to find the subscriber. The switchover times you report are consistent with Google's VoIP infrastructure holding a call and silently dialing/connecting it on the other network.

It would be interesting to see if voice handoffs still worked if IP networking was unavailable on the phone.

Re: Network handover in Google Fi

#23

Post by chrisBob »

dgulino wrote: post #15

https://republicwireless.com provides seamless wifi->cell and cell->wifi handover of calls.

There is a connection between Google (or is it Alphabet) and Bandwidth.com (the Republic Wireless parent company) that I can't quite figure out. Google Voice is mostly based on Bandwidth.com technology, and Republic Wireless and Google Fi are very similar products. Republic Wireless even claims they are about to release a dual-carrier option like Project Fi which they call Tempo.

It is possible that they are just competing, but it seems like there is more of a link there.

Re: Network handover in Google Fi

#24

Post by ndrarmst »

a-dub wrote: post #22

"Given that two different profiles exist on the Fi SIM, the Fi software must have the capability to switch between them. SIM cards are actually little computers, so by developing an application that runs on the SIM card Google could trigger a switch based on any of the information the SIM has access to – the network it is registered on, the receipt of a trigger SMS, or something else. My guess is that the SIM card co…

The counterargument to an all-software solution is that if you switch the profile on the Fi phone, it also remains switched if you move the SIM to another device. So however selection was made, it is 'sticky' across devices.

That's why I guessed it was a paired SIM app + intelligent Android app - but I couldn't verify that, so you could be correct.

Re: Network handover in Google Fi

#25

Post by ndrarmst »

Bedon292 wrote: post #20

Very interesting. This contradicts how Google advertises the service though. They say the transition is seamless. Unless they are playing fast and loose with the definition of seamless, this does not seem to qualify. According to their website it is expecting signals to slowly get worse and have time to start transitioning before it drops out. A sudden loss of wifi for whatever reason probably confuses it. I would ex…

Driving between dead zones of opposite carriers is surprisingly difficult to do - would have been a great test, though!

I did test walking down the street away from Wi-Fi - the transition is much smoother, but I was only able to get it down to about 2 seconds or so. And that was when I turned around and ran back toward Wi-Fi when it started to switch, so that the call remained good on Wi-Fi until it actually cut over.

Re: Network handover in Google Fi

#26

Post by arkieguy »

I'm pretty sure the testing methodology in this article is flawed. Using the manual switching codes (which are NOT recommended by Google) shouldn't be used to evaluate the vast majority of situations. For instance, doing timing on a manual network switch isn't necessarily equivalent to the phone automatically switching. Also, doing a manual switch and then extrapolating that the phone doesn't automatically switch back is not valid.

Basically, you can't test any of the automated functionality using manual codes!

Re: Network handover in Google Fi

#28

Post by arkieguy »

Bedon292 wrote: post #20

Very interesting. This contradicts how Google advertises the service though. They say the transition is seamless. Unless they are playing fast and loose with the definition of seamless, this does not seem to qualify. According to their website it is expecting signals to slowly get worse and have time to start transitioning before it drops out. A sudden loss of wifi for whatever reason probably confuses it. I would ex…

His premise that switching isn't seamless is based on his use of manual switching codes (something that Google advises against).

Re: Network handover in Google Fi

#29

Post by a-dub »

ndrarmst wrote: post #24
a-dub wrote: post #22

"Given that two different profiles exist on the Fi SIM, the Fi software must have the capability to switch between them. SIM cards are actually little computers, so by developing an application that runs on the SIM card Google could trigger a switch based on any of the information the SIM has access to – the network it is registered on, the receipt of a trigger SMS, or something else. My guess is that the SIM card co…

The counterargument to an all-software solution is that if you switch the profile on the Fi phone, it also remains switched if you move the SIM to another device. So however selection was made, it is 'sticky' across devices. That's why I guessed it was a paired SIM app + intelligent Android app - but I couldn't verify that, so you could be correct.

Usually radio stuff happens on a dedicated processor which has limited communication with the application processor that runs Linux/Android/Java/Userland. (think like a modem, in some cases they are literally controlled with serial links and AT like text commands).

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

I believe that profile swaps would be sticky, but actual processing on the SIM is going to be extremely limited and active management of the radios most likely will take place in baseband firmware.

Android talks its baseband processors by interfacing with a daemon called rild (Radio Interface Layer (Library?) daemon) which loads a binary blob library which actually does the talking to the baseband chip.

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