thanks for your help! just as a short info inbetween, while we are still trying to fix the problem. the cirpack of our carrier always receives dtmf-inputs as inband tones (because, at least in germany, all dtmf-inputs are sent over the landline as inband tones). because we always had problems with the carriers cirpack and fs in conjunction with inband tones (sometimes they where sent two or three times), our carrier added rfc-2833 to their cirpack. now the carrier sends both: rfc-2833 AND inband tones. the problem is, that the carrier tells us, that the cirpack can not filter the inband tones, so that they just can send rfc-2833. but they tell us, that they add some stops (or something like this) to the inband tones, so that the inband tones are not functional anymore. but this does not seem to work correctly. if we listen to dtmf-inputs only on fs, we do not have any problems, because fs ignores the inband tones and only reacts to the rfc-2833 signal. therefor we never had any problems. now, we have a project, where not fs listens to the dtmf-inputs, but a callcenter on the other side (outbound). therefor the cirpack has to send clean dtmf-inputs to the callcenter. but we believe, that the cirpack on the outgoing side is receiving his own inband tones AND rfc-2833 signals from the incoming side of the cirpack. so the cirpack on the outgoing side send his own inband tones PLUS the converted rfc-2833 signals to the other side (callcenter). we have to go on testing. we spoke with someone from nokia about their iwsd and they told us, that they filter all inband tones, so that we only receive rfc-2833. we will do some testing with them. but i wonder, why the nokia iwsd can filter inband tones and the cirpack can't. any ideas? will keep you informed, what we found out.