Seamless switching from gprs to wifi calling

kenneth marken k-marken at
Fri Jun 8 07:21:28 CEST 2007

mathew davis wrote:
> Dear community,
> I am not sure if this is a widely known thing or not, but I just found 
> out about it and had some questions about this working on the neo.  
> T-mobile has hotspots all around my area, but have been experimenting 
> with a new service called T-mobile HotSpot @Home.  It uses a UMA 
> (unlicensed mobile access) technology to allow phones to switch from 
> cellular connection to Wi-Fi connection.  And also makes it possible for 
> VoIP calls.  So this is something that is very interesting to me only I 
> would like it to be a little different, I don't want to use T-Mobile's 
> service I would like to use my Wi-Fi connection to my VoIP of choice.  I 
> know this has been talked about before with some options including an 
> Astrex box forwarding the call to your cellphone until your in range 
> then switching to Wi-Fi but that was not a very seamless transistion 
> from my understanding.  So I guess my question is could we impliment a 
> UMA type of technology for the neo that is customizable to use our VoIP 
> provider?  Or since that particular part is locked we wouldn't have 
> access to that part?  Just curious. When I get the phone I will be 
> playing with trying to find a solution to this problem.  I have very 
> limited knowlege about this kind of thing.  I am not an experianced 
> programmer yet.  I only have about 3 yers of indestry experiance, but 
> none of that is mobile development and almost none of it is linux 
> related, so I have a bit of a learnign curve so that is why I am asking 
> the question here. 

while not fully up to speed on how it all works, here is my quick take 
on it:

as long as its a voip connection, and said voip service allows two ip's 
to share a account and call, there should be little to no problem having 
both a wifi and gprs connection open at the same time as one moves about 
(in my experience a gprs connection can be held open but not used). 
hell, one may even use bluetooth if it can handle the data transfer.

the problem here is that ip thing. UMA has a normal mobile phone 
connections as one option so therefor dont have to think about multiple 
ip's. it just need to have a internet connected cell so to speak, and 
only hand the call over when the ip based connection is fully in place.

however im guessing there are some issues with going between two wifi 
zones/networks or something similar...

so mostly you need a voip service that allows you to log in from another 
ip without booting the old connection off or hanging up any calls. after 
that its mostly a case of the client software figuring out what of the 
two connections to send on. or maybe just send on both, expecting the 
service to throw away the data thats a duplicate. something that i think 
is a basic feature in mobile phone systems.

one funny thing is that if your using voip, and have a flat rate data 
plan for your mobile phone, there is no need to go wifi anyways as the 
mobile data connection will probably be more reliable given that its 
already built to do what one is trying to make the wifi system do 
(handover, multiple connections and overlapping zones).

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