pisoiu
Joined: 31 Dec 2002
Posts: 891
Helped: 24
Location: Romania
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 11 Aug 2006 20:20 Why data call dosn't complet???? |
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The CSD connection is like a connection between landline modems. For example, you can dial from the GSM phone at a phone number where a landline modem is listening, and if you answer with it, the connection will establish. After the connection is established, your GSM modem will most likely will respond with "CONNECT" message (or its numerical equivalent), then you can perform data transfers through the serial port. You can monitor the hardware signals to view the state of the connection (ex. DCD line will signal when your connection is active if this option is configured properly with AT commands - look at the modem's datasheet) and it is advisable to use flow control during the transfers, in order to avoid data loss due to the connection performance. Most likely, when your connection is dropped, you will receive a message on the serial port, and the DCD line will become inactive. The transfers through this method are raw transfers, no packet receive method is implemented, no acknowlergements over data transfer, no nothing.
As far as I know (but I am not 100% sure), there are no special parameters which must be set in order to make CSD connections, but the option must be activated by your GSM provider.
If you want to make reliable data transfers, it is advisable to use GPRS transfers, almost all GSM modems are GPRS capable. Also, the CSD data calls are taxed per minute, but GPRS connections are taxed per quantity of information transferred.
/pisoiu
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