I have a problem regarding calls to GSM Modems (9600baud) via a Cisco Voice Gateway.
ATA186 ------SCCP-----CUCM 7.1.3b ------H.323------IOS Gateway 2811------ISDN/BRI/PRI-------PSTN
or
VG224 ------SCCP-----CUCM 7.1.3b ------H.323------IOS Gateway 2811------ISDN/BRI/PRI-------PSTN
or
VG224 ------H.323------IOS Gateway 2811------ISDN/BRI/PRI-------PSTN
If I call a specific GSM Modem with a normal analog phone not connected to the Cisco CUCM (e.g. from home) I get a modem tone. When I call this Modem from an analog phone connected to a VG224), I get the debug (isdn q931) output: "Service/option not available, unspecified", and the call gets dropped. I've tried this from 3 other Cisco CUCM installations (and 3 providers), but its the same everywhere. The customer needs this service though. Calls to normal modems (e.g. analog internet connection) work fine with modem pass-through. I even tried without the CUCM using a VG224 with H.323.
Am I correct in assuming that the Voice Gateway is the problem? Does anybody have any advice?
Edited: I was informed that the V.120 protocol needs to be supported for a Cisco Router to dial in to a GSM Modem. Is this protocol needed on the Voice Gateway?
