[Asterisk-Users] Help wanted getting Busy / Congested working properly

[Dan A]

Hi all,
I have Asterisk sat between the PSTN and a PBX.  The connection to both is
E1 PRI.  The span connected to the PSTN has a signalling type of pri_cpe;
the span connected to the PBX is set to pri_net.

When people from the PSTN call a line on the PBX which is engaged, the
line just sits there silently until they hang up.  The only way I have
found to give them a busy tone is by doing an Answer() before Busy() -
however this is not what I want to do as it means the calling party will
be billed for a call which did not go through, and equipment which deals
with busy signals in a different way (e.g. mobile phones, which can
normally automatically retry on busy) does not work properly.

The relevant section of the dialplan is:
[globals]
PSTN=ZAP/g1        ; The channel to the PSTN

[from-pbx]
exten => _9X.,1,Dial(${PSTN}/${EXTEN:1})
exten => _9X.,2,Playtones(congestion)
exten => _9X.,3,Congestion
exten => _9X.,102,Playtones(busy)
exten => _9X.,103,Busy

I have also tried it without the Playtones() and with Answer() before
Congestion() / Busy().

I've had reports that people making outgoing calls to numbers which are
engaged have the same problem.

Does anyone know what I could be doing wrong?  Extensive Gooling and
Wiki-reading haven't turned anything up.

Thanks,
Dan