U1911 IP-PBX is used. Outgoing calls to 2 different mobile operators are made using the same prefix. Calls to one operator are working fine, calls for the other operator are not working. For the case in which the calls are not working, after customer dials the outgoing number, he can hear the RBT one time, then the call simply disconnects without any tone or voice prompt.
Giving the fact that all the tested numbers from the first Mobile operator were successful and the outgoing prefix used was the same for any outgoing call to mobile networks, but the calls to the second Mobile operator failed, we suspected that the problem is in the recognition of the busy tone sent by the second mobile operator.
After detecting the busy tone with the command:
config start monitor osu tone slot X port Z (X is the number of the OSU board, Z is the number of the OSU board port used)
and changing the tone detection parameters according to the tone detection test, all the outgoing calls started were successful.