from time to time, we get so-called simplex / one-way audio calls, where one party cannot hear the other. The only thing in common is that is does happen with calls via SIP trunk, not ISDN and not internal calls. Nothing strange in verbose and SIP logs. Could even be some weird intermittent firewall issue I guess.
Apart from logging all traffic 24/7 via tcpdump (not really convenient), can you give me some ideas how to debug this kind of issue?
Asterisk 1.8.11-cert10 on CentOS 6.3, if that matters.