i found a problem on th Zoiper Softphone.
When Zoiper connects via iax2 to the Asterisk and i make an outgoing call over ISDN(PSTN) the incomming voice is very bad, so i here only pieces from the otherone, he can hear me normal.
But when i switch to sip, or i use the Idefesk 1.37 it works normal.
i got an answer from zoiper.
They said that Asterisk sends 16ms frames and zoiper can´t handle this.
How can i say Asterisk to send 20ms frames?
But this ist only from PSTN to iax2.