1. How does GoIP select a GSM channel when making an outgoing call?

GoIP only requires to select GSM channels for outgoing calls when it is configured as Single Server mode, Config. By Group mode, or Trunk Gateway mode. In order to spread out the channel usage evenly, the automatic channel selection algorithm chooses the idle channel that is used the least (in terms of the number of calls made).

2. Can I configure GoIP so that it answers my VoIP call first and then let me to dial out a number via one of its GSM channels (Second dial operationa)?

Yes, you can. You need to the GoIP to use Single Server mode, Config. By Line mode, or Config. By Group mode and enable the CALL OUT via GSM option in the Call Management page. Please leave the Forward Number in this section blank. The operation described here is referred as Second Dial.

3. Can I configure GOIP so that I can call one of its GSM channel numbers and then let me make a VoIP call (Second dial operation)?

Yes, you can. You need to the GoIP to use Single Server mode, Config. By Line mode, or Config. By Group mode and enable the CALL IN via GSM option in the Call Management page. Please leave the Forward Number in this section blank. The operation described here is referred as Second Dial.

4. Why is GoIP dialing out a wrong number?

There are two reasons that GoIP dials out a wrong number.

a) For call termination from VoIP to GSM, the number received is not a valid E.164 number (PSTN and GSM numbers). Please use the Dial Plan parameter to modify the number received, so that it is a valid number. For international calls, please make sure that the country code and/or area code are added. In addition, you need to make sure that long distance call service is available for the SIM card inserted.

b) For second dial operation, GoIP needs to detect the number (DTMF digits) to be dialed from the incoming voice stream. It is possible that the number is detected incorrectly and consequently, the number dialed out is wrong.

For VoIP calls termination to GSM, the DTMF dialing method of the calling device should be set to DTMF outband signaling (RFC2833 / SIP INFO). If RFC2833 method is used, the payload type should be matched with the server.

For DTMF detection (inband DTMF dialing) method, you can try to tune the parameter DTMF Tone Dropout. This helps to avoid the same digit detected twice if dropouts occurs during a single DTMF tone duration. Please refer to the GoIP User Manual for more information.