[asterisk-ss7] Asterisk/libSS7 functionality question

[Mark Wilkinson]

Hello,
    I have a question about the functionality of SS7 in Asterisk.
 From what I can work out, at present, I can not do the following :-

I want a  call to be placed from a PBX to Asterisk.
Have Asterisk playback a message or do other clever stuff,
then release the call back to the original PBX,
without the call remaining looped (tromboned) through Asterisk.

 From what I understand of SS7, it should be possible to get a SS7 PBX
switch to take back the call and transfer it elsewhere - Somewhat similar
in functionality to a SIP refer.

If I've understood, and please correct me where I'm wrong, the 
chan_dahdi driver
in the asterisk trunk needs the 'transfer' functionality adding to allow 
it to signal
to the PBX a request for call take back possibly by implementing the FAR 
FAC FAA
messages ?

Thanks In Advance
Mark Wilkinson.