True mobile wifi phone

Hi all,

I am new here, and working on a wifi phone project. I have one simple question. Is there a true mobile wifi phone out there? By true mobile I meant calls would not be cut off while hopping from one hotspot to another.

The answer depends on what you call a "hot spot". There are many phones that will move from one access point to another on the same network - meaning in the same IP range where the same IP address can be used across many access points (this also works in small networks if you plug access points in "bridge mode" into a single AP/router and it works in the Meraki "mesh network" environment).

In other cases, where there are independent AP/routers with different IP ranges (or even with the same IP range if left at the default -- normally 192.168.0.x or 192.168.1.x -- but unaware of each other), then hand over is much less likely as the pone would need to get a new local IP and contact the server via a different public IP. In most cases, all of this takes too long for a hand over.

Sorry didn't make myself clear enough. I was refering to the second case where access points are unaware of each other. It is correct that the phone needs to get a new local ip (sometimes might be the same) and contact the server via a different public ip, and will take a relatively long time for the hand over. However, if the phone has more than one wifi connections, wouldn't the hand over process be made almost instantaneous?

If the phone has more than one WiFi connection AND the server knows what to do with more than one registration from different public IPs, then the answer (in theory) would be yes. On the other hand, I don't know of any equipment that actually does this.

I don't the reason for phone to have more than one registration or the server needs to handle multiple registration from a single entity. If the phone wants to hop over to a different subnet during a conversation, it can send some sought of reinvite (with new extenal ip and port) message to the server, un-register itself and re-register with the new external ip address.

Yes, you can do with reinvites, but it's not fast enough to be practical (some hotspots can take 15 seconds to register in the first place).

That's why the workable (maybe) solution would be to have simultaneous logins at all times, assuming you're in range of multple AP's.

One other choice that may work - but may not be exactly what you are looking for - is to go with a UMA based GSM phone (such as offered by T-Mobile USA). In that case, the phone can hand from one WiFi hot spot to the public GSM network, then have time to connect through another hot spot and take the call back from GSM on the next hot spot.

If you are looking for something equivalent to fully mobile/GSM running over WiFi, I don't expect that you will find anything.

dean :

Yes, you can do with reinvites, but it's not fast enough to be practical (some hotspots can take 15 seconds to register in the first place). That's why the workable (maybe) solution would be to have simultaneous logins at all times, assuming you're in range of multple AP's.

Yes. I do expect the software to login to multiple hot spots simultaineously through multiple wifi network interfaces. While a call is going on through one wifi connection, the other wifi interfaces will constantly scan the area seeking an AP that has the strongest signal and logins to it.

Quote:

While a call is going on through one wifi connection, the other wifi interfaces will constantly scan the area seeking an AP that has the strongest signal and logins to it.

It's probably do-able, but I doubt it's do-able very well and imagine the business case for it is probably unjustified. In a scenario where the user is moving, cellular is a better candidate.

Mesh networks are a different animal, and much better suited to moving targets.

(welcome to VoIP User btw!)

Hi

Well a good start for light reading will be http://www.nada.kth.se/utbildning/grukt ... _06159.pdf

Also have a google for GSM and dect handover as the theory is very similar. A big problem for all is too many networks/APs to choose from, no too few.

Ian

Thanks. Definitely will read.