Busy tone after Hangup

Dear all,

i have configured an Asterisk server connected to an E1 line, i have also configured some extensions (100, 101, 102).
If an internal extension calls an external number using the PSTN line, when the external phone closes the call, for about 30 seconds the caller (internal) listens a busy tone.

Is it possible to avoid this behaviour? Can Asterisk detect this tone and hangup the call immediately?

Thanks and regards,