Seamless switching from gprs to wifi calling

[Luit van Drongelen]

I'll have to come back on this... I've read several stories about
t-mobile's hotspot at home service lately, and it seems like t-mobile
made it possible to let it switch between UMA and airwaves. I
intentionally don't call it seamless, because it isn't. (yet?) Several
reports say it takes a second or two to switch between WiFi and GSM
airwaves

--
Luit

On 6/10/07, Luit van Drongelen <openmoko at luitvd.net> wrote:
> Hi,
>
> As I said, to do the T-Mobile thing, you'd need a GSM/UMA backbone
> that's capable of routing calls through both. Though I don't think
> it's easy to reroute (hand over) a call from one of the protocols to
> the other. It requires timing, which requires computing power, which
> requires a mighty strong backbone for all the people using the
> service. So my guess is that T-Mobile's Hotspot services only lets you
> use one of the two protocols. As long as you're near a hotspot, you're
> logged in to the UMA backbone, and your phone number is assigned to
> that hotspot service. If you're not logged in, incoming and outgoing
> calls are routed through GSM normally.
>
> And there's the problem for doing it yourself. You can't really decide
> for yourself where the calls for your number are routed to. The
> service provider decides, and without a "T-Mobile Hotspot @ home"-like
> service backbone, you can't do this. You can either call through WiFi
> using SIP, but it'll use your SIP number, not your GSM number. And
> vice-versa.
>
> It's all up to the service provider to enable goodness like this... :(
>
>
> --
> Luit
>
> On 6/8/07, mathew davis <someoneinjapan at gmail.com> wrote:
> > Thanks for all the input.  Sounds very interesting.  I didn't realize that
> > UMA isn't VoIP.  I don't want to use t-mobiles system.  I was thinking of
> > how I could do it without using their system, but the same idea.  Sounds
> > like I have got a lot fo reading ahead of me and that this problem is bigger
> > than I thought it would be.  Just to make sure I got every thing right GPRS
> > is to slow.  Inorder to get something like this to work you need the
> > following:  Client software capable of handling 2 streams sip and gsm.  It
> > also has to know when to hand over from one to the other.  You also need a
> > server that can handle the 2 streams and know when to throw away the extra
> > data.  Does that sound right?  Just want to make sure I understand what you
> > guys wrote.  That IMS thing sounds interesting I will have to do some
> > research on that.  Thanks for the info.
> >
> >
> >
> > On 6/8/07, Luit van Drongelen <openmoko at luitvd.net> wrote:
> > > To get back to what Mathew asked: I don't think a T-Mobile
> > > HotSpot at home is switching calls back and forth as you get in reach of
> > > a hotspot, and walk away from it. Secondly: this only works with
> > > T-Mobile! (for now) T-Mobile has probably set up a HotSpot at home call
> > > server near their GSM traffic backbone, on which your phone logs in,
> > > and through which your GSM traffic goes (with that UMA protocol) while
> > > you're logged in (in reach of a public (T-mobile) hotspot). Calls that
> > > already take place can't be re-routed I guess...
> > >
> > > Anyway, what I'm trying to say is that firstly: you need T-Mobile as
> > > your operator. Secondly: you need that T-Mobile HotSpot @home plan.
> > > Thirdly: you need a phone that's capable of routing your GSM traffic
> > > through UMA, to the T-Mobile UMA server/backbone/whatever they call
> > > it. As for the Neo1973 and OpenMoko: The phone can most likely do it,
> > > because the software just needs to know how to do it. BUT, I don't
> > > think T-Mobile will tell you how to log in. T-Mobile makes the phone
> > > software themselves for a reason. If they show you how to make a phone
> > > log in, you can make a program that logs your computer in too. So a
> > > FOSS solution for this probably won't come easily.
> > >
> > > --
> > > Luit
> > >
> > > PS: sorry for the double post Johnson, it bounced because I mailed
> > > from the wrong account
> > >
> > > On 6/8/07, Al Johnson < openmoko at mazikeen.demon.co.uk> wrote:
> > > > Check the archives for a full discussion of this. In short GPRS is
> > unsuitable
> > > > for VoIP because of the high latencies, often in seconds. The GSM data
> > mode
> > > > is more suitable even though it's only 9600. It should be possible to
> > have
> > > > Asterisk route calls to the right VoIP endpoint, or to a GSM voice call
> > if it
> > > > can place calls to the PSTN. The trick comes in knowing when to hand
> > over,
> > > > and having a unified client that'll get Asterisk to do it.
> > > >
> > > > On Friday 08 June 2007 06:21, kenneth marken wrote:
> > > > > 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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