Callers intermittently cannot hear Agent

We have an intermittent issue where callers cannot hear the agent but the agent can hear the caller. Thoughts on where to begin troubleshooting?

One-way audio problems almost always fall into one of two categories:

  1. RTP issues from a firewall intercepting the incoming packets of the audio traffic coming into the server from ports 10000-20000. If you have inbound calls from a service provider, you should “whitelist” that provider to allow all of the UDP traffic in the audio stream. There are some situations where this isn’t technically necessary, but it’s a reasonable practice to allow your ITSP to send all traffic from their servers to your PBX, especially if it is behind a firewall. Also, make sure that your NAT settings are correct for your server and that you are only using routable addresses in the real world. If you are passing your “192.168.0.x” address out to the world, you can cause this problem as well.

  2. Chan-SIP to/from PJ-SIP transcoding errors. We have seen a recent spate of issues where people using Chan-SIP for their external ITSP connections and PJ-SIP for their internal phones are losing the audio due to error in codec transcoding. I think this is probably a temporary issue and part of the growing pains of PJ-SIP, but if this sounds like your issue, you need to carefully examine all of your connections to make sure they are using the same codec. Start by disabling all codecs and then add just one. If you are in the US, start with uLaw for everything, otherwise use aLaw. If you find that these work, you can continue to add codecs until you recause the problem. Since there are many codecs and some sound better than others, it might take some experimentation to figure out exactly which codec set works best in your application.

Thanks for the response Dave. Unfortunately, I am new to the phone world and I am not sure where to begin looking based on your responses.

It’s all English. What are you having trouble with? I can’t help you understand anything if I don’t know what you are not understanding.

Google “one way audio Asterisk firewall” and start learning. You’re the admin - this is your job. We can help, but we can’t learn it for you.