On Thu, 1 Dec 2011, Rohan McLeod <rhn@jeack.com.au> wrote:

James Harper wrote:

...

Google is giving me conflicting answers... I want to dial a remote gsm device via my iPhone plugged in to a PC but I'm not seeing anything that looks like it might be a modem when I do lsusb. This is obviously different than just having a data connection to the internet as the remove device isn't connected to the internet - I need to dial it directly.

I have a fairly antiquated NextG handset which can function as a mobile 'router'; via a USB cable or WiFi. My understanding is that it is still capable of sending and receiving calls in this situation.

Have you tested that? The last time I tried to use a smart-phone for calls and data the data stopped when the call started. It's really annoying when you have ssh'd to a server and the client calls to ask if it's fixed yet... Apparently you need to either have a phone with two 3G antenna (which is really rare) or a phone that can do calls over GSM while 3G data transfer is in progress. Hardware to support voice over GSM and data over 3G is apparently reasonably common, but software support isn't so good. NB This is generic telephony stuff, I'm not an expert on it and I don't know much about the iPhone.

Are you sure the iPhone can't dial out while connected to the PC ? In which case I can't see why it would care whether the remote device was; gsm ,3g, NextG or 4G.

They apparently want to have a direct data connection between two smart-phones without either being connected to the Internet. I doubt that this will be possible unless they use IP over SMS or something equally horrible.

Even if you are trying to do VOIP over the data channel I would have thought the phone company associated with the service would still hide the complexities of the mobile technology of the remote device from users .......or is there something which I am not understanding ?

Phone companies do a really poor job of hiding the complexities. If you put a different SIM in your phone you have to configure a new APN to connect to the Internet! How hard would it have been to design some way for the SIM to store the APN data - or even for the OS such as Android to have a list of the APNs for all the telcos in the region and the bigger ones in other regions? A file with about 20K of data could have all the APNs that you are ever likely to need and a lot more and that would not be noticed in the gigabytes of storage that modern phones have. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/

On Thu, 1 Dec 2011, "James Harper" <james.harper@bendigoit.com.au> wrote:

A smart phone talking to a GSM modem attached to a fixed roadside device actually. They just don't want to have a separate GSM modem for the PC/laptop when they have a perfectly functional iPhone which they always have on them. Ultimately they will probably be using Windows to make the connection, but I'm testing with Linux. Because it's better :)

What does "GSM modem" really mean in this situation? There is no requirement to use the ISP Internet service to transfer packet/stream data over GSM. Some years ago some people I knew developed encrypted GSM phones which encrypted the encoded voice data and then sent it in the same way that regular GSM voice data is sent. The phones usually encode voice to data, compress it, and then GSM provides the ordered packet layer. Well they just added an extra encryption step. There's no technical obstacle to running something like PPP or a virtual serial port instead of encrypted voice in that situation, and the people I knew probably developed just that as a first stage towards their end goal. There's lots of different ways of doing these things, many of which can save a few dollars each on the cost of the multitude of devices in the field while adding to the hassle at the server end. Most of these things would be impractical to try and reverse engineer unless you have a great desire to learn about mobile phones. Of course such things would preclude using an iPhone as they are too locked down to be convenient for such things. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/

On 1/12/11 5:25 PM, Russell Coker wrote:

Apparently you need to either have a phone with two 3G antenna (which is really rare) or a phone that can do calls over GSM while 3G data transfer is in progress. Hardware to support voice over GSM and data over 3G is apparently reasonably common, but software support isn't so good.

The 3G standard used worldwide (UMTS) does support simultaneous voice and data. There could be a million different factors why it doesn't work at a particular time. I'm certain that I have taken calls while 'tethered' up to a laptop before.

- or even for the OS such as Android to have a list of the APNs for all the telcos in the region and the bigger ones in other regions? A file with about 20K of data could have all the APNs that you are ever likely to need and a lot more and that would not be noticed in the gigabytes of storage that modern phones have.

There already is a mechanism - /system/etc/apns-conf.xml . I believe this file is empty in the Android Open Source distribution. Pester your manufacturer if they do not include a full worldwide list. Many custom Android distributions do have them. On 1/12/11 10:54 AM, James Harper wrote:

Can the iPhone be used as a GSM modem or is that deemed too 'legacy' these days? I'm hoping there is a usb switch app I can run to enable the modem USB interface but I'm not optimistic.

Highly doubt you will be able to - on older smartphones the modem could be made available over USB but this has died out in favor of tethering. I doubt any current smartphones could, either. a) The USB client functionality is in the kernel, you would need to add the relevant bits there to bridge between USB and the modem b) Even then the modem may not have a traditional serial interface - on those that do, it is merely an emulation layer coded into the radio firmware, and the purpose James wants ('circuit switched data' as it is called), it probably won't implement that. - Mathew

On 1/12/11 11:45 PM, James Harper wrote:

...

The 3G standard used worldwide (UMTS) does support simultaneous voice and data. There could be a million different factors why it doesn't work at a particular time. I'm certain that I have taken calls while 'tethered' up to a laptop before. Does this apply if you are in a reception area that doesn't get a 3G signal and you're stuck with EDGE/GSM?

As far as I am aware, no.