Our Free switch (FS) call flow is as follows :

1)Originator user agent contacts FS with an INVITE
2)FS sends an INVITE to a Dynamic Routing Engine (DRE)
3)DRE returns possible routes using a SIP 300 Multiple Choice
4)FS bridges the call

The problem : Our reporting system needs to track the exact hunt info including channel name and hangup cause of each hunt which is attempted based on the reply from the DRE. This causes multiple b legs to be generated which needs to be tracked, grouped and finally parsed to generate a report.

The solution : A small change in the code that makes every b leg save its hangup cause and channel name in the originator session (a leg) as a channel variable so now we only need to parse a single a leg XML cdr to get all call related info.