Re: Data over normal GSM call

[Harald Welte]

On Tue, Apr 15, 2008 at 11:17:19AM +0200, Stefano Cavallari wrote:
> On Monday 14 April 2008 21:00:34 Harald Welte wrote:
> > On Sun, Apr 13, 2008 at 07:57:02PM -0500, Hans L wrote:
> [...]
> > AFAIR, the DTMF key press is encoded and send over the Um (air)
> > interface to the BTS/BSC/MSC and then in the end converted into
> > actual audible sounds.
> >
> > Please see Page 22 of http://www.chu.edu.tw/~lhyen/wc/gsm.pdf for a
> > graphical illustration how this works.
> 
> This imply that there is a data channel available. Can you trasmit anything 
> else that DTMF? What is the bandwidth of this channel?

no, there is no data channel.  The START/STOP DTMF messages are part of
the layer 3 signalling messages (sent over a signalling channel that is
also used for call setup/teardown).

also, that signalling channel is between the MSC and the telephone.


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Re: Data over normal GSM call

[Stefano Cavallari]

On Monday 14 April 2008 21:00:34 Harald Welte wrote:
> On Sun, Apr 13, 2008 at 07:57:02PM -0500, Hans L wrote:
[...]
> AFAIR, the DTMF key press is encoded and send over the Um (air)
> interface to the BTS/BSC/MSC and then in the end converted into
> actual audible sounds.
>
> Please see Page 22 of http://www.chu.edu.tw/~lhyen/wc/gsm.pdf for a
> graphical illustration how this works.

This imply that there is a data channel available. Can you trasmit anything 
else that DTMF? What is the bandwidth of this channel?

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Re: modulated data over GSM voice (was Re: Data over normal GSM call)

[Andy Green]

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Hash: SHA1

Somebody in the thread at some point said:

| While stating it being unlikely, I have no dout that it can be done,
| given enough effort.  But it requires a lot of work by somebody with

Alright, that's all I was saying too.

| lots of knowledge and experience in signal processing, baseband digital
| communications, modulation schemes, the intrinsic properties of the
| various codecs involved.
|
| Oh, and even if you do that, you still have to manage to implement it
| all based on fixed-point math, make it run next to all the other things
| on the ARM920T CPU core :)

Hey in my last job I did this, there is a great GPL library called
hawkvoice that has integer GSM codec and plenty of others.

http://www.hawksoft.com/hawkvoice/

Four encode instances worked great on no-FP 180MHz ARM at way less than
100% CPU.

| Not to forget the testing on the various codecs that are in use.  GSM
| networks are getting more diverse every year.  With some carriers now

"Impractical"... not worth the time to look at... I guess so... but it's
not the same as "impossible".

- -Andy
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Re: modulated data over GSM voice (was Re: Data over normal GSM call)

[Harald Welte]

On Mon, Apr 14, 2008 at 10:15:06PM +0200, Adrian-Ken Rueegsegger wrote:
>
> Harald Welte wrote:
>> Just to give you a "summary judgement":
>>
>> Running any kind of voice-encoded data over a regular voice channel of a
>> GSM phone is _extremely_ unlikely to work.
>>
>> There are a number of different codecs in use.  Which codec is
>> determined by the network.  There is echo cancellation at potentially
>> multiple locations during the call.  There might be one or multiple
>> transcoders of the voice codec along the road.
>>
>> If you can manage to design a modulation and coding scheme that survives
>> all (or even most) of the stages above, I think you have achieved
>> something great.  I doubt you will get more than 300bps though :)
>
> Somebody already has. May I point you towards the paper "Real Time End  
> to End Secure Voice Communications over GSM Voice Channel" by N.N.  
> Katugampala, K.T. Al-Naimi, S. Villette, and A.M. Kondoz [1].

While stating it being unlikely, I have no dout that it can be done,
given enough effort.  But it requires a lot of work by somebody with
lots of knowledge and experience in signal processing, baseband digital
communications, modulation schemes, the intrinsic properties of the
various codecs involved.

Oh, and even if you do that, you still have to manage to implement it
all based on fixed-point math, make it run next to all the other things
on the ARM920T CPU core :)

Not to forget the testing on the various codecs that are in use.  GSM
networks are getting more diverse every year.  With some carriers now
operating their BTS's behind IP links (Abis-over-IP), I only can make
vague guesses what additional jitter, delay (and potential transcoding)
this might imply to the network.

All I wanted to point out is that it is unlikely that general-purpose
developers like most community members (including myself) can come up
with something that works in any reasonable time frame.

> [2]. Nevertheless highly interesting to read :)

Yes, thanks a lot.

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Re: modulated data over GSM voice (was Re: Data over normal GSM call)

[Ian Stirling]

Harald Welte wrote:

Just to give you a "summary judgement":

Running any kind of voice-encoded data over a regular voice channel of a
GSM phone is _extremely_ unlikely to work.

There are a number of different codecs in use.  Which codec is
determined by the network.  There is echo cancellation at potentially
multiple locations during the call.  There might be one or multiple
transcoders of the voice codec along the road.

If you can manage to design a modulation and coding scheme that survives
all (or even most) of the stages above, I think you have achieved
something great.  I doubt you will get more than 300bps though :)



It has been done - for the minimal case of going through two actual real 
phones.

1300bps.
Basically a voice synthesizer driven by data, and a voice recognition 
system on the other end.
It uses the very properties that GSM/... codecs for speech are intended 
to preserve in the face of small amounts of bit errors - synthesizing an 
artificial throat, and exciting this model with data, so you don't get 
into parts of the codec that are chaotic or horribly lossy.


Unfortunately, I can't find the original paper I found.



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Re: modulated data over GSM voice (was Re: Data over normal GSM call)

[Adrian-Ken Rueegsegger]

Harald Welte wrote:

Just to give you a "summary judgement":

Running any kind of voice-encoded data over a regular voice channel of a
GSM phone is _extremely_ unlikely to work.

There are a number of different codecs in use.  Which codec is
determined by the network.  There is echo cancellation at potentially
multiple locations during the call.  There might be one or multiple
transcoders of the voice codec along the road.

If you can manage to design a modulation and coding scheme that survives
all (or even most) of the stages above, I think you have achieved
something great.  I doubt you will get more than 300bps though :)


Somebody already has. May I point you towards the paper "Real Time End 
to End Secure Voice Communications over GSM Voice Channel" by N.N. 
Katugampala, K.T. Al-Naimi, S. Villette, and A.M. Kondoz [1].


The authors claim to have achieved a throughput of 3 kbps with a 2.9% 
BER.  By adding error correction codes the throughput went down to 1.2 
kbps with a BER of 0.03%. Unfortunately they have not released any code 
and I could not find much detail beyond a couple more  papers found at 
[2]. Nevertheless highly interesting to read :)


-Adrian

[1] - 
http://personal.ee.surrey.ac.uk/Personal/N.Katugampala/pubs/eusipco05.pdf

[2] - http://personal.ee.surrey.ac.uk/Personal/N.Katugampala/

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modulated data over GSM voice (was Re: Data over normal GSM call)

[Harald Welte]

Just to give you a "summary judgement":

Running any kind of voice-encoded data over a regular voice channel of a
GSM phone is _extremely_ unlikely to work.

There are a number of different codecs in use.  Which codec is
determined by the network.  There is echo cancellation at potentially
multiple locations during the call.  There might be one or multiple
transcoders of the voice codec along the road.

If you can manage to design a modulation and coding scheme that survives
all (or even most) of the stages above, I think you have achieved
something great.  I doubt you will get more than 300bps though :)

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Re: Data over normal GSM call

[Harald Welte]

On Sun, Apr 13, 2008 at 07:57:02PM -0500, Hans L wrote:
 
> Although the transfer of audio data over cell phone audio is very
> lossy, there is at least one standard, proven way of transferring data
> by phone: DTMF(http://en.wikipedia.org/wiki/DTMF).

please note though, that if you send DTMF over your mobile phone, the
DTMF tone is generated by the network, _NOT_ inside the phone.

Your phone is required to generate the tone, too.  But that tone is only
played through the ear speaker to the user, it is not sent over the
voice channel.

AFAIR, the DTMF key press is encoded and send over the Um (air)
interface to the BTS/BSC/MSC and then in the end converted into 
actual audible sounds.

Please see Page 22 of http://www.chu.edu.tw/~lhyen/wc/gsm.pdf for a
graphical illustration how this works.

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Re: Data over normal GSM call

[Gilles Casse]

Hans L wrote:
> This thread gave me an idea which I haven't seen discussed before,
> though it's probably not useful for the situation the original poster
> had in mind.
>
> Although the transfer of audio data over cell phone audio is very
> lossy, there is at least one standard, proven way of transferring data
> by phone: DTMF(http://en.wikipedia.org/wiki/DTMF).
>

This idea seems to me very attractive!

This tiny URI could enrich the audio stream (from phone, FM,...) like a 
paper can be enriched with QR code, or a video with asterpix: 
http://www.asterpix.com


Great!

Gilles


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Re: Data over normal GSM call

[Fabian Olesen]

On Mon, Apr 14, 2008 at 3:33 AM, Fabian Olesen <[EMAIL PROTECTED]>
wrote:

>
>
> On Mon, Apr 14, 2008 at 2:57 AM, Hans L <[EMAIL PROTECTED]> wrote:
>
> >
> > The standard tones allow up to 16 values to be represented at a time,
> > so it would be like transferring data in base16 (aka hex or 4 bits at
> > a time).  According to wikipedia, the minimum length of a tone should
> > be 70ms, which would limit data transfer to roughly 56 bits/second.
> > Of course this is very slow and unusable if you are thinking in terms
> > of web browsing, but could be useful for transmitting small amounts of
> > data such as URIs or other connection information(an IP address is
> > only 32bits).  The URIs could be accessed immediately if the receiving
> > end has a simultaneous internet connection, or saved for later.
>
>
> This could actually work
>
> But it would require that both ends have a specialised phonestack
> (openmoko fx)
> where some kind of protocol was inplemented for listening for DTMF with a
> start and stop signal,
> where the phone would know not to send the tones into the ear piece,
> so that it would not scream into the other user's ears.
>
> after a little research, i came across the Goertzel algorithm (Wikipedia
link) 


-- 

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Re: Data over normal GSM call

[Fabian Olesen]

On Mon, Apr 14, 2008 at 2:57 AM, Hans L <[EMAIL PROTECTED]> wrote:

>
> The standard tones allow up to 16 values to be represented at a time,
> so it would be like transferring data in base16 (aka hex or 4 bits at
> a time).  According to wikipedia, the minimum length of a tone should
> be 70ms, which would limit data transfer to roughly 56 bits/second.
> Of course this is very slow and unusable if you are thinking in terms
> of web browsing, but could be useful for transmitting small amounts of
> data such as URIs or other connection information(an IP address is
> only 32bits).  The URIs could be accessed immediately if the receiving
> end has a simultaneous internet connection, or saved for later.


This could actually work

But it would require that both ends have a specialised phonestack (openmoko
fx)
where some kind of protocol was inplemented for listening for DTMF with a
start and stop signal,
where the phone would know not to send the tones into the ear piece,
so that it would not scream into the other user's ears.



-- 

Mvh
Fabian Olesen


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Re: Data over normal GSM call

[Hans L]

This thread gave me an idea which I haven't seen discussed before,
though it's probably not useful for the situation the original poster
had in mind.

Although the transfer of audio data over cell phone audio is very
lossy, there is at least one standard, proven way of transferring data
by phone: DTMF(http://en.wikipedia.org/wiki/DTMF).

The standard tones allow up to 16 values to be represented at a time,
so it would be like transferring data in base16 (aka hex or 4 bits at
a time).  According to wikipedia, the minimum length of a tone should
be 70ms, which would limit data transfer to roughly 56 bits/second.
Of course this is very slow and unusable if you are thinking in terms
of web browsing, but could be useful for transmitting small amounts of
data such as URIs or other connection information(an IP address is
only 32bits).  The URIs could be accessed immediately if the receiving
end has a simultaneous internet connection, or saved for later.

Example 1: Automatically transferring a call from GSM to VOIP.
1) During a call, user A tells his phone to send VOIP connection info to user B.
2) User A's phone sets up "listening" over VOIP, and send it's
connection info via DTMF
3) User B's phone receives the DTMF signals and decodes them
4) User B's phone asks confirmation to attempt VOIP connection, and
user B accepts
5) Phone attempts VOIP connection.  If successful, the GSM connection
is terminated, and conversation continues over VOIP.

Example 2: Sending a file during a call(a camera phone picture,
e-business-card, etc).
1) During a call, user A snaps a picture and chooses to share it with user B
2) The phone uploads the file to some central repository* and sends
file URI(via DTMF) to user B.
3) User B's phone receives the DTMF signals and decodes them
4) User B's phone asks confirmation to download file
5) If user B accepts, her phone attempts to download from that URI
6) If declined(or user B does not currently have an internet
connection), URI can still be saved in a call history log to be
accessed later.

Example 3: sending GPS coordinates...(more or less same concept as
previous two examples).  It only requires the sending of two floating
point numbers(maybe single precision, requiring only 64bits, is
sufficient in this case, not sure).

-Hans Loeblich

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Re: Data over normal GSM call

[thomasg]

That's not all, there are even more factors:
Mic -> A/D converter -> Codec (depends on net and quality: up to 5 different
codecs possible) -> Radio -> Air-Interface -> Radio ->Codec -> Voice Quality
Enhancer (VQE - who knows what this will do with your data, maybe just
dropping it at all) -> and the same way backwards, with different codecs.
And most important: there is no TCP or similar - you just can't know what
the other side will get.

On Fri, Apr 11, 2008 at 9:37 PM, Ian Stirling <[EMAIL PROTECTED]>
wrote:

> Diego Fdez. Durán wrote:
> 
>
> >
> > Can't you initiate a voice call between to FreeRunners and then use the
> > mic and mixer devs to modulate the data as sound?
> >
>
> Broadly yes.
>
> The problem is:
>
> A human making mobile - mobile call looks something like this.
>
> 1 microphone
> 2 analog-digital converter
> 3 GSM encoder
> 4 radio transmission
> 5 Add errors due to sunspots
> 6 radio reception
> 7 GSM decoder
> 8 ISDN-like 8KHz 8 bit sampling over mobile companies network
> 9 Public switched telephone network
>
> And then back again in reverse - with all the codec senses flipped.
>
> Any analog modem signal has to get through the GSM codec - twice - and
> survive bit errors. GSM is designed so that single bit errors make
> audibly similar output - but not similar numerically.
>
> The GSM codec is basically designed to throw away anything that is not
> voice-like.
>
> If you have a perfect radio channel, and can get at the digital data
> that would normally go to/from the codec (step 3) it won't help much for
> 'normal' modems - as you still have the GSM encode/decode cycle at the
> network side.
>
> In reality, what you have to do to push any sort of data through this
> link is to basically have a data-driven vocoder at one side, that
> gabbles - but makes sounds that could in principle be made by human
> throats, and a voice recogniser at the other end. This can get
> 1300bits/sec.
>
> CSD - 'data' GSM calls are different.
> Instead of using the normal GSM codec, they use a special codec that is
> designed for error-free data transmission.
> This can be broken out and transmitted over the normal phone network and
> end up in a device like an ISDN modem.
> Some ISPs 'normal' modems actually support this by default, so dialing
> just works.
> However, though this would be really nice to use - it's not free, and in
> many countries/telcos costs significant amounts to enable.
>
>
>
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Re: Data over normal GSM call

[joerg]

Am Fr  11. April 2008 schrieb Stefan Misch:
> Hi,
> 
> I just talked about this issue with a colleague who uses an HTC PDA with 
windows 
> mobile. For the data connection he uses a dial-up connection as a modem. He 
> doesn't have a data plan but a flat fee for voice calls into land lines.
> 
> He says he gets about up to 4K/s which is not much of course but it's still 
> possible to view light websites or emails with it. (I would not want to use 
it 
> with Google Maps for example which is one of the key features why I would 
want 
> mobile internet access.)
> 
> So I don't think it's impossible. Maybe the hardware and the codecs are 
> different on OpenMoko but I doubt that this is an obstacle that cannot be 
overcome.
> 
> All best,
> Stefan

That's simple CSD (see other posts of this thread). AFAIK it's supported by 
all carriers in Germany. I used it ~year2000 with a Nokia 6210 and a Palm5 on 
O2 without any problem. You can access internet via provider's accesspoint, 
or you can dial up a modem connected number at your home to run your own 
accesspoint/proxy. Anyways it's normal connection fee (as of y2k).

cheers
jOERG

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Re: Data over normal GSM call

[Ian Stirling]

Diego Fdez. Durán wrote:



Can't you initiate a voice call between to FreeRunners and then use the
mic and mixer devs to modulate the data as sound?


Broadly yes.

The problem is:

A human making mobile - mobile call looks something like this.

1 microphone
2 analog-digital converter
3 GSM encoder
4 radio transmission
5 Add errors due to sunspots
6 radio reception
7 GSM decoder
8 ISDN-like 8KHz 8 bit sampling over mobile companies network
9 Public switched telephone network

And then back again in reverse - with all the codec senses flipped.

Any analog modem signal has to get through the GSM codec - twice - and
survive bit errors. GSM is designed so that single bit errors make
audibly similar output - but not similar numerically.

The GSM codec is basically designed to throw away anything that is not
voice-like.

If you have a perfect radio channel, and can get at the digital data
that would normally go to/from the codec (step 3) it won't help much for
'normal' modems - as you still have the GSM encode/decode cycle at the
network side.

In reality, what you have to do to push any sort of data through this
link is to basically have a data-driven vocoder at one side, that
gabbles - but makes sounds that could in principle be made by human
throats, and a voice recogniser at the other end. This can get 1300bits/sec.

CSD - 'data' GSM calls are different.
Instead of using the normal GSM codec, they use a special codec that is
designed for error-free data transmission.
This can be broken out and transmitted over the normal phone network and
end up in a device like an ISDN modem.
Some ISPs 'normal' modems actually support this by default, so dialing
just works.
However, though this would be really nice to use - it's not free, and in
many countries/telcos costs significant amounts to enable.


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Re: Data over normal GSM call

[Stefan Misch]

Hi,

I just talked about this issue with a colleague who uses an HTC PDA with windows 
mobile. For the data connection he uses a dial-up connection as a modem. He 
doesn't have a data plan but a flat fee for voice calls into land lines.


He says he gets about up to 4K/s which is not much of course but it's still 
possible to view light websites or emails with it. (I would not want to use it 
with Google Maps for example which is one of the key features why I would want 
mobile internet access.)


So I don't think it's impossible. Maybe the hardware and the codecs are 
different on OpenMoko but I doubt that this is an obstacle that cannot be overcome.


All best,
Stefan

ramsesoriginal wrote:

By applying some sort of modulation (fm? am? psm?) it should be
possible to transfere data over gsm, but on a much lower speed then
through the data channel.

On Thu, Apr 10, 2008 at 7:34 PM, Harald Welte <[EMAIL PROTECTED]> wrote:

On Tue, Apr 08, 2008 at 10:22:10AM -0400, Dan Staley wrote:
 > Does anyone know if it is legal (in the standard TOS) with providers
 > (such as ATnT) to send data over a normal phone call?

 this is not possible, since regular voice calls for GSM are not
 bit-transparent, i.e. the voice signal is coded and potentially re-coded
 (transcoded) a number of time between the calling and receiving party.

 Data calls over GSM are done using CSD.  They also use quite a lot more
 error correction than voice calls.

 --
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Re: Data over normal GSM call

[ramsesoriginal]

By applying some sort of modulation (fm? am? psm?) it should be
possible to transfere data over gsm, but on a much lower speed then
through the data channel.

On Thu, Apr 10, 2008 at 7:34 PM, Harald Welte <[EMAIL PROTECTED]> wrote:
> On Tue, Apr 08, 2008 at 10:22:10AM -0400, Dan Staley wrote:
>  > Does anyone know if it is legal (in the standard TOS) with providers
>  > (such as ATnT) to send data over a normal phone call?
>
>  this is not possible, since regular voice calls for GSM are not
>  bit-transparent, i.e. the voice signal is coded and potentially re-coded
>  (transcoded) a number of time between the calling and receiving party.
>
>  Data calls over GSM are done using CSD.  They also use quite a lot more
>  error correction than voice calls.
>
>  --
>  - Harald Welte <[EMAIL PROTECTED]>   http://openmoko.org/
>  
>  Software for the world's first truly open Free Software mobile phone
>
>
>
>  ___
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>



-- 
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Re: Data over normal GSM call

[Harald Welte]

On Tue, Apr 08, 2008 at 10:22:10AM -0400, Dan Staley wrote:
> Does anyone know if it is legal (in the standard TOS) with providers
> (such as ATnT) to send data over a normal phone call?

this is not possible, since regular voice calls for GSM are not
bit-transparent, i.e. the voice signal is coded and potentially re-coded
(transcoded) a number of time between the calling and receiving party.

Data calls over GSM are done using CSD.  They also use quite a lot more
error correction than voice calls.

-- 
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Software for the world's first truly open Free Software mobile phone

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Re: Data over normal GSM call

[Andy Green]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1

Somebody in the thread at some point said:
| Diego Fdez. Durán writes:
|> On Tue, April 8, 2008 18:02, Joe Pfeiffer wrote:
|>> Andy Green writes:
|>>> -BEGIN PGP SIGNED MESSAGE-
|>>> Hash: SHA1
|>>>
|>>> Somebody in the thread at some point said:
|>>> | On ti, 2008-04-08 at 16:02 +0100, Andy Green wrote:
|>>> |> I think you're right, but just a thought if you could issue
|>>> ready-coded
|>>> |> GSM codec frames, you can put the data direct in there for
| 1KBytes/sec
|>>> |
|>>> | Yeah, but you can't.
|>>>
|>>> "can't" is pretty strong... isn't "not without seriously hacking
|>>> something around" better?
|>> If I understand the limitation correctly, in this case, I think
|>> "hacking something around" involves hacking at least firmware and
|>> quite possibly hardware inside the gsm modem.  That's close enough to
|>> "can't" that the difference really doesn't matter.
|>>
|> Can't you initiate a voice call between to FreeRunners and then use the
|> mic and mixer devs to modulate the data as sound?
|
| Yes -- but that's the technique with the claimed limitation of roughly
| 1Kbps.  It isn't inserting the raw gsm codec frames.

Right... but there is a guy in Openmoko .tw who recompiles our firmware,
subject to whatever license agreement we have, he does actually change
it.  The "can't" reduces to the architecture of the data pump in the
chips and the licence agreement in this case.  Just saying that "can't"
makes some assumptions about, eg, who is trying.  (I seriously doubt we
consider for one second to target this case, just making a philosophical
point about the absolute dangers of absolutism ;-) )

- -Andy
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Re: Data over normal GSM call

[joerg]

Am Di  8. April 2008 schrieb Tilman Baumann:
> Tilman Baumann wrote:
> 
> > Maybe CSD is billed like a voice call. I never used it, but i don't 
> > remember any special charges for that.
> 
> I dug deeper. Seems like this is true.
> 
> But this raises the question if the Neo can do CSD. Probably it does, 
> since the GSM module does not appear to be somehow intentionally crippled.
> 
> 9.6 kBit/s is no fun though...

Right, the Neo calypso modem speaks "AT" on the internal serial interface. I 
don't think there is any problem with the very much Hayes standard 
AT-commands for CSD. Nearly every phone could do this even 1999. IIRC there 
even is a 14400B/s mode (at least for networks/areas with support for 
EFR-codec), and I'm quite sure this isn't charged differently for 
mobile-originated calls.
For Mobile-Terminated calls however, you usually need a second special "data" 
number linked to your simcard. Otherwise the GSM.network wouldn't know 
whether or not to set the data-flag for the connection, what means they send 
the POTS-modem's sound over GSM "as is", instead of recoding it to digital 
prior to sending it over the air. This might not apply for MT-ISDN-calls, 
with data-service flag set for the originating device.

HTH
cheers
jOERG

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Re: Data over normal GSM call

[Joe Pfeiffer]

Diego Fdez. Durán writes:
>
>On Tue, April 8, 2008 18:02, Joe Pfeiffer wrote:
>> Andy Green writes:
>>>-BEGIN PGP SIGNED MESSAGE-
>>>Hash: SHA1
>>>
>>>Somebody in the thread at some point said:
>>>| On ti, 2008-04-08 at 16:02 +0100, Andy Green wrote:
>>>|> I think you're right, but just a thought if you could issue
>>> ready-coded
>>>|> GSM codec frames, you can put the data direct in there for
>>> >1KBytes/sec
>>>|
>>>| Yeah, but you can't.
>>>
>>>"can't" is pretty strong... isn't "not without seriously hacking
>>>something around" better?
>>
>> If I understand the limitation correctly, in this case, I think
>> "hacking something around" involves hacking at least firmware and
>> quite possibly hardware inside the gsm modem.  That's close enough to
>> "can't" that the difference really doesn't matter.
>>
>>
>
>Can't you initiate a voice call between to FreeRunners and then use the
>mic and mixer devs to modulate the data as sound?

Yes -- but that's the technique with the claimed limitation of roughly
1Kbps.  It isn't inserting the raw gsm codec frames.

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Re: Data over normal GSM call

[Diego Fdez . Durán]

On Tue, April 8, 2008 18:02, Joe Pfeiffer wrote:
> Andy Green writes:
>>-BEGIN PGP SIGNED MESSAGE-
>>Hash: SHA1
>>
>>Somebody in the thread at some point said:
>>| On ti, 2008-04-08 at 16:02 +0100, Andy Green wrote:
>>|> I think you're right, but just a thought if you could issue
>> ready-coded
>>|> GSM codec frames, you can put the data direct in there for
>> >1KBytes/sec
>>|
>>| Yeah, but you can't.
>>
>>"can't" is pretty strong... isn't "not without seriously hacking
>>something around" better?
>
> If I understand the limitation correctly, in this case, I think
> "hacking something around" involves hacking at least firmware and
> quite possibly hardware inside the gsm modem.  That's close enough to
> "can't" that the difference really doesn't matter.
>
>

Can't you initiate a voice call between to FreeRunners and then use the
mic and mixer devs to modulate the data as sound?
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-- 
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Re: Data over normal GSM call

[Joe Pfeiffer]

Andy Green writes:
>-BEGIN PGP SIGNED MESSAGE-
>Hash: SHA1
>
>Somebody in the thread at some point said:
>| On ti, 2008-04-08 at 16:02 +0100, Andy Green wrote:
>|> I think you're right, but just a thought if you could issue ready-coded
>|> GSM codec frames, you can put the data direct in there for >1KBytes/sec
>|
>| Yeah, but you can't.
>
>"can't" is pretty strong... isn't "not without seriously hacking
>something around" better?

If I understand the limitation correctly, in this case, I think
"hacking something around" involves hacking at least firmware and
quite possibly hardware inside the gsm modem.  That's close enough to
"can't" that the difference really doesn't matter.

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Re: Data over normal GSM call

[Tilman Baumann]

Mikko Rauhala wrote:


A quick glance finds mostly mentions of 1st gen analog mobiles having
been used with modems, and notably "At the same time, the speech
oriented audio compression used in GSM actually meant that data rates
using a traditional modem connected to the phone would have been even
lower than with older analogue systems."


The Wikipedia article is somewhat misleading here.

CSD is real data transfer over the GSM network which is translated via 
Gateways into PSTN modem calls. A service of the GSM network.


Somehow they managed to mix that modem via voice stuff into the CSD article.
(Or at least this is how i undrstood this. *g* )

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Re: Data over normal GSM call

[Andy Green]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1

Somebody in the thread at some point said:
| On ti, 2008-04-08 at 16:02 +0100, Andy Green wrote:
|> I think you're right, but just a thought if you could issue ready-coded
|> GSM codec frames, you can put the data direct in there for >1KBytes/sec
|
| Yeah, but you can't.

"can't" is pretty strong... isn't "not without seriously hacking
something around" better?

- -Andy
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Re: Data over normal GSM call

[Mikko Rauhala]

On ti, 2008-04-08 at 17:16 +0200, Tilman Baumann wrote:
> Maybe CSD is billed like a voice call. I never used it, but i don't 
> remember any special charges for that.

Doubtful for the US "drop your pants and bend over, please" carriers'
"minutes"; I presume the original poster was in this situation from
his .edu account and mention of AT&T.

Here in Finland we're mostly billed by minute (though there are
_optional_ US-like plans), and CSD calls indeed cost pretty much the
same as voice calls. I presume the situation may be similar in many
other (esp. EU) countries as well, which is good for us if we want to do
eg. those encrypted phone calls or cheaper international calls via
VOIP/CSD, but doesn't help the original poster.

> The Wikipedia article about CSD has some hints about running voice 
> modems via GSM too.
> http://en.wikipedia.org/wiki/Circuit_Switched_Data

A quick glance finds mostly mentions of 1st gen analog mobiles having
been used with modems, and notably "At the same time, the speech
oriented audio compression used in GSM actually meant that data rates
using a traditional modem connected to the phone would have been even
lower than with older analogue systems."

-- 
Mikko Rauhala <[EMAIL PROTECTED]>
University of Helsinki


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Re: Data over normal GSM call

[Tilman Baumann]

Tilman Baumann wrote:

Maybe CSD is billed like a voice call. I never used it, but i don't 
remember any special charges for that.


I dug deeper. Seems like this is true.

But this raises the question if the Neo can do CSD. Probably it does, 
since the GSM module does not appear to be somehow intentionally crippled.


9.6 kBit/s is no fun though...

Regards
 Tilman

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Re: Data over normal GSM call

[Tilman Baumann]

Mikko Rauhala wrote:

On ti, 2008-04-08 at 10:22 -0400, Dan Staley wrote:

I have plenty of cell minutes (not to mention free calls between certain
numbers...) but I dont want to pay for a data planso I figure if I
wanted to, I could just have my phone call my computer and transfer data
over the line.


There has been talk of it (especially in connection to encrypted
phonecalls). The archives have a lot of it.

To summarize, you can't transfer very useful amounts of data over a GSM
voice call since we can't bypass the GSM chip's audio codec for those.
Obviously you can get some data through, but the highest anyone's gone
was IIRC ~1k using some kind of funky phonetic coding, but I believe
there was no exact reference to this either, let alone code (which would
be rather complex).


Maybe CSD is billed like a voice call. I never used it, but i don't 
remember any special charges for that.


The Wikipedia article about CSD has some hints about running voice 
modems via GSM too.

http://en.wikipedia.org/wiki/Circuit_Switched_Data

Regards
 Tilman

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Re: Data over normal GSM call

[Mikko Rauhala]

On ti, 2008-04-08 at 16:02 +0100, Andy Green wrote:
> I think you're right, but just a thought if you could issue ready-coded
> GSM codec frames, you can put the data direct in there for >1KBytes/sec

Yeah, but you can't.

-- 
Mikko Rauhala <[EMAIL PROTECTED]>
University of Helsinki


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Re: Data over normal GSM call

[Andy Green]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1

Somebody in the thread at some point said:
| On ti, 2008-04-08 at 10:22 -0400, Dan Staley wrote:
|> I have plenty of cell minutes (not to mention free calls between certain
|> numbers...) but I dont want to pay for a data planso I figure if I
|> wanted to, I could just have my phone call my computer and transfer data
|> over the line.
|
| There has been talk of it (especially in connection to encrypted
| phonecalls). The archives have a lot of it.
|
| To summarize, you can't transfer very useful amounts of data over a GSM
| voice call since we can't bypass the GSM chip's audio codec for those.
| Obviously you can get some data through, but the highest anyone's gone
| was IIRC ~1k using some kind of funky phonetic coding, but I believe
| there was no exact reference to this either, let alone code (which would
| be rather complex).
|
| You could perhaps do stuff like update GPS coordinates through DTMF or
| something like that, but for larger data transfer needs you really want
| a data plan.

I think you're right, but just a thought if you could issue ready-coded
GSM codec frames, you can put the data direct in there for >1KBytes/sec
or so.  It still has GSM frame format just not GSM data really in the
payload.  Of course what is on the other end has to realize you played
that game or it will sound very strange.

- -Andy

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Re: Data over normal GSM call

[Mikko Rauhala]

On ti, 2008-04-08 at 10:22 -0400, Dan Staley wrote:
> I have plenty of cell minutes (not to mention free calls between certain
> numbers...) but I dont want to pay for a data planso I figure if I
> wanted to, I could just have my phone call my computer and transfer data
> over the line.

There has been talk of it (especially in connection to encrypted
phonecalls). The archives have a lot of it.

To summarize, you can't transfer very useful amounts of data over a GSM
voice call since we can't bypass the GSM chip's audio codec for those.
Obviously you can get some data through, but the highest anyone's gone
was IIRC ~1k using some kind of funky phonetic coding, but I believe
there was no exact reference to this either, let alone code (which would
be rather complex).

You could perhaps do stuff like update GPS coordinates through DTMF or
something like that, but for larger data transfer needs you really want
a data plan.

-- 
Mikko Rauhala <[EMAIL PROTECTED]>
University of Helsinki


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Re: Data over normal GSM call

[Matt Manjos]

I don't know about specific cases, but I think that cell phone
companies are more concerned about people using VOIP over data over
gsm voice calls.

There was talk earlier about writing a fax program that uses incoming
calls to receive faxes, and that GSM couldn't transmit decent faxes
because of a quality or bandwidth problem, but I can't remember the
specifics. This might hinder such a setup.

Matt

On Tue, Apr 8, 2008 at 10:22 AM, Dan Staley <[EMAIL PROTECTED]> wrote:
> Does anyone know if it is legal (in the standard TOS) with providers
>  (such as ATnT) to send data over a normal phone call?
>
>  I have plenty of cell minutes (not to mention free calls between certain
>  numbers...) but I dont want to pay for a data planso I figure if I
>  wanted to, I could just have my phone call my computer and transfer data
>  over the line.
>  Has anyone else looked into this?
>
>  -Dan Staley
>
>
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Data over normal GSM call

[Dan Staley]

Does anyone know if it is legal (in the standard TOS) with providers
(such as ATnT) to send data over a normal phone call?

I have plenty of cell minutes (not to mention free calls between certain
numbers...) but I dont want to pay for a data planso I figure if I
wanted to, I could just have my phone call my computer and transfer data
over the line.
Has anyone else looked into this?

-Dan Staley


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