On some site, video platform is interconnected with ngn platform, there is one-way audio problem when video platform is calling pstn in private, the pstn terminal can hear pstn, but pstn cannot hear video terminal.
After communicating, we realize that there is a port checkout on TM8010, which is the source port is opposite to the destination port. But VP8520 is sent via appointed port, so it is masked off by TM8010. Communicate with the engineer and close port checkout. The call is normal.
In private network, the media flow of video terminal is: video terminal-VP8520-TMG8010-gateway. Catch packet on VP8520 and TM8010, find that the send and receive media flow is normal on VP8520 and TM8010. So it is not the network cause.