Sorry for my poor english. I am running a FreeSWITCH box on Debian Linux, connecting with China Telecom IMS (shenzhen). I found a surprising problem that no audio when dial to specific number (eg 10000, China Telecom custom service number). Dial other nubmers with FreeSWITCH, like mobile phone number (tested with China Telecom, China Unicom, China Mobile) works well. I captured the traffic between FreeSWITCH box and IMS, found that no media was send by IMS. And I tested microSIP, it works well with no such a problem. I don't konw much about SIP and other protocols, please help me. FreeSWITCH log and captured packet from FreeSWITCH and microSIP attatched. Others can be applied if needed. Thanks. FreeSWITCH version: 1.6.19-36-7a77e0b~64bit (-36-7a77e0b 64bit) (From official repository) Linux version: Debian GNU/Linux 8.10 (jessie)