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2 posts

Wannabe Geek


Topic # 9855 18-Oct-2006 22:24
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hi guys

i have a tons of questions about circut switched data and it seems like there's nothing to read about this technology over the internet, too old, so I realy need you'r help here..

i understand that the main use for csd is creating a point to point connection between my cellular and a server (like an isp for connceting the internet) via a special data channel, am I right? so my first question is how's the gsm networks knows I'm interest in a csd call and create that data channal? is there a device (in the network) that identify it's not voice?

my second question is, is there an option to create a csd connection between two cellular phones?(I know there are encryptors for gsm that use csd) how does it works? (how is the network informing the targeted cellular phone a csd connection is created to him?)

I also understand that fax service is used over csd connection, does it says that PSTN number can create a csd connection to a cellular phone?(or the fax service is only for sending faxes and not receiving?) and if it is possible, so how does the GSM network knows that the call is a csd, i mean, in the PSTN network there isn't any special DATA cahannal, it's all voice, so hows the GSM network knows it's a csd call and not voice?

oh, and 1 last quation, how's csd calls are going globally ?(let's say while roaming), i suppose there isn't any special data channel in the international link that GSM providers use, so the voice and data are transmitting together, how are they being seprated after it?

does any one know's the answer for some of the questions? (or have a link for a good article about csd?)

thanks

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902 posts

Ultimate Geek
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  Reply # 49032 19-Oct-2006 11:03
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gsmiscomplicated: i understand that the main use for csd is creating a point to point connection between my cellularand a server (like an isp for connceting the internet) via a special data channel, am I right? so my first question is how's the gsm networks knows I'm interest in a csd call and createthat data channal? is there a device (in the network) that identify it's not voice?

For outgoing calls, it's part of the call setup process (your gsm modem says 'this is a data call')

For incoming calls, it's tied in with the mobile phone number. That's why you have 3 phone numbers when you get CSD enabled: voice, data, fax.

gsmiscomplicated: my second question is, isthere an option to create a csd connection between two cellular phones?(I know there are encryptors for gsm that use csd)how does it works? (how is the network informing the targeted cellular phone a csd connection is created to him?)


I've never tried it but I'd imagine it'd work just like a normal modem to modem call. Just dial the other phone's data number (and have that phone/PC set up to answer incoming data calls)

gsmiscomplicated: I also understand that fax service is used over csd connection, does it says thatPSTN number can create a csd connection to a cellular phone?(or the fax service is only for sending faxes and not receiving?) and if it is possible, so how does the GSM network knows that the call is a csd, i mean, in the PSTN network there isn't any special DATA cahannal, it's all voice,so hows the GSM network knows it's a csd call and not voice?


See above

gsmiscomplicated: oh, and 1 last quation, how's csd calls are going globally ?(let's say while roaming), i suppose there isn't any special data channel in the international link that GSMproviders use, so the voice and data are transmitting together, how are they being seprated after it?


It's only encoded as a GSM CSD call while on the air interface. As soon as it hits the vocoder (either in the base station controller or the mobile switch depending on the operator) it's back to standard 64 kbit/s like any other call. The type of recipient it goes to from there is out of the hands of the GSM provider.





 



2 posts

Wannabe Geek


  Reply # 49213 21-Oct-2006 09:38
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thanks alot for the answer, now it makes much more sense ,that's the CSD service is tied in with the mobile phone number.
but are you sure you always get 3 diffrent phone numbers (voice, data, fax)? I heard that some GSM providers do it and some don't.. you think there can be any other soultion?

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