Hello,
I can help you on troubleshooting your quality issues and call failures and recommend how to improve.
Im a VoIP engineer with more than 8 years on troubleshooting diferent kind of VoIP and network issues on level 3 (last level with R&D), having worked at full time job in a vendor of big telco operators.
I have good experience with Asterisk and A2B.
Regards
Samuel