[Asterisk-Dev] suggestions/discussion how to implement ISDN advice of charge (AOC) from low level channel driver through channels to the dialplan and back and to the cdr

[Frank Sautter]

hi,

i used the last few weeks in research and implementation of advice of
charge (AOC) messages Q.956 atop of Q.932 on ISDN (E1-PRI) connections.

the ASN.1 decoding and encoding of the AOC-E-units APDUs in the libpri
is done and reports it's results as debug messages. because my insight
and oversight regarding the communication between the the low level
channel drivers (e.g. libpri), the channel (chan_zap) and the pbx part
is very limited, i would like to ask some experienced developers how to
implement this feature.

what i would like to achieve is:
* account incoming AOC-E messages in the call detail records.
* generate AOC-E messages to connected devices (e.g. another pbx) (they
must be transmitted in the call clearance phase of the call on E1-PRIs).
* when the asterisk server is spliced between an existing pxb and an
E1-PRI from a telco, the incoming AOC messages from the telco should be
forwarded to the pbx. maybe some calculations on the received AOCs would
be nice (e.g. multiplying by a factor, a base cost per call, converting
from charged units to charged currency,...).

currently not implemented but desirable features are:
* AOC-D (charged units during the call).
* AOC-E-currency (currency) (german telcos don't deliver this).

later it would be nice to support more uncommon features like:
* AOC-S (advice of charge during call setup).
* generation of AOC messages based on rulesets (local calls, voip calls,
domestic calls, mobile calls, international calls, a.s.o.).

i need some suggestions how to solve these problems:
* how should i propagate the AOC information to the dialplan.
* how can i trigger the sending of a AOC information during the call
clearance phase to a connected PBX.
* how can i find out which channels are bridged together (between which
channels i have to forward the AOC messages).
* how to define if a AOC message should be forwarded or not (config
and/or dialplan).
* how could cyclic AOC-D messages be generated.

any suggestion or a disscussion is very welcome, as it would reduce the 
time i have to search through those thousands of lines of code dramatically.

regards
  frank sautter