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I want to know if I can call a GSM modem (a SIEMENS MC55) from a normal analog (PSTN) modem. If so, how do I have to configure the GSM and the analog device? I've read about the +FCLASS and +CSNS commands but the connection doesn't work - I'm getting a BUSY or NO CARRIER. Are there other requirements?

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  • \$\begingroup\$ Do you get a RING on the GSM modem and are you answering it? \$\endgroup\$ – pjc50 Nov 8 '12 at 10:55
  • \$\begingroup\$ @pjc50 The GSM device is build into a metering device. I can see in the log a 'Attempt to dial in'. Can I configure a 'automatic answer'? \$\endgroup\$ – sebastian Nov 8 '12 at 11:24
  • \$\begingroup\$ I would expect that to be possible, but obviously the software on the other end has to support it. \$\endgroup\$ – pjc50 Nov 8 '12 at 11:31
  • \$\begingroup\$ @pjc50 I can set initialization strings for the GSM device, is there a command to enable auto-answer? \$\endgroup\$ – sebastian Nov 8 '12 at 11:54
  • \$\begingroup\$ Check your documentation, but "ATS0=1" is standard. \$\endgroup\$ – pjc50 Nov 8 '12 at 14:57
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After extending the initialization string of the GSM modem with 'AT+CSNS=4' the device was able to connect with analog modems.

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