One way audio when connected to a wireless/wired network, but not over 3G/4G data

Having an annoying issue when connecting to a wireless network - I can connect and register to the freepbx server just fine (using Zoiper client for iOS). but there’s only one way audio.

For example:

I dial the echo test number (*43) from my iOS SIP client but I hear no audio from the PBX. If I disconnect from the wireless network and use my carriers 4G data and try the call again I get two way audio as you would expect to get.

The same occurs with an actual call; when I dial my SIP number from a desk phone connected to a standard telephone line, I answer the call on my iOS client and the desk phone gets audio from me (the iOS client on my phone) but I cannot hear any audio from that desk phone.

I also get the same issue when calling my SIP number from a Windows SIP client (Zoiper again) on my works network - the desk phone can hear audio from the Windows SIP client, but the SIP client cannot hear audio from the desk phone.

I’m a novice when it comes to freepbx, picking up a lot of my knowledge from either Reddit or YouTube videos. The PBX itself is directly connected to the internet using its own public IP and is not behind any router or firewall (so no NAT in play, and it doesn’t live on a private network (RFC1918)). The only firewall is the one that freePBX has built in. Could this be any of the NAT settings within freePBX itself? It’s curious how (with the softphone on my iPhone) that it’ll work over my carriers 4G data but not when connected to a wireless network, which leads me to suspect some mis-configured NAT settings on the PBX.

Any help welcomed!

I’d take that bet in a heartbeat. One way audio is almost always a NAT issue.

Everything I’ve read suggests that too. The problem is, as far as i can see it looks like it’s configured right. Under “Settings > Asterisk SIP Settings” on the General SIP Settings tab, “NAT” displays the correct external address (which is the same address as the network interface has anyway), and “Local Networks” is set to the same sub net that the interface address is in (auto detected).

Then over on the Chan SIP Settings tab, “NAT” is set to no, and “IP Configuration” is set to “Public IP”. From there, I’m not sure what else I could check or adjust.

NAT settings for the individual chan_sip extensions are as set on the Advanced tab when editing extensions.

and the individual devices will also have a NAT setting at their end. Make sure that both ends properly identify that they are NAT devices if there is ever a chance that the connection (like your your 3G network settings) might have a NAT hop in it.

Looks like that was it - did not know that was there! It was set to no, so have set it to yes which it suggests will work for internal and external. Tested from soft phone client on iOS and Windows laptop from network office, and it works OK.

Thank you both!

Note that the default for this setting is configurable in Advanced Settings.

It might suggest that, but it isn’t really so. NAT settings (for any device, either the server or a phone) are so that a remote end can know how to set up the packets to transit a Network Address Translation device. So, setting NAT on a phone tell the phone to tell the server “This is how to find me.” Setting NAT on the PBX is there to inform the phone on how to get back to the PBX. Both have to be set correctly to make sure that all of the possible combinations of intervening NAT devices can be successfully navigated.

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