No Audio on Internal Extension Calls 70% of the Time.

[rake-support]

Environment:
Unsupported SIP (Twilio),
3cx Version 16.0.0.1581
Yealink T41S Phones
running in Linux/Debian in Azure (previously running on windows and had the same issue)

Whenever we dial an internal extension.. about 70% of the time.. the person can head the phone ring, and pick it up..but there is no audio on either side. No one can hear anyone. This happens whether the extension is pulled up from the Phone book, or dialed directly. On occasion, the calls do work, and both parties can be heard. We don't have very high usage on the mgmt console.. so I don't think that is it. And if you dial the Complete number .. you get audio 100% of the time.. this only affects internal extensions.

Does anyone have any advice on what to look at? How to Troubleshoot this? The Firewall checker comes back and says everything is ok.... If anyone even has an IDEA about what to check, please let me know.

Thanks,
Darrell

 

[leejor]

And what is your set up? Are the sets local to the server, using an SBC, VPN, STUN? All sets at the same location?

 

[rake-support]

All handsets are provisioned by 'Local Lan'... 6 of the Phones are in one location.. and 2 are remote... Server is in Azure.. so none of them are truly 'local'

 

[leejor]

So how are you connected to the server? SBC, STUN? You are still not providing a lot of details.

 

[rake-support]

I'm sorry.. I'm not super familiar with VOIP systems.. This just became my responsibility.. We do not have any SBC Hardware, so i'm assuming we are connecting through STUN. I have access to the 3cx console.. where can I find out how we are connecting?

 

[BrenttG]

Edit each extension, and set in the Options tab at the bottom, PBX Delivers Audio to enabled, and report back...

As for the SBC idea they threw out, here's the thing, if you had an SBC, it would say the phones were using it on the Phones tab in 3CX, if at the far right there is only the IP address and nothing about an SBC, then there is no SBC, also, if there was an SBC, and it was down, your phones would not be working at all most likely, it wouldn't be intermittent....

 

[leejor]

You could check the 3CX Activity Log to see how the PBX is communicating with each set. Are they each addressed by the public IP and a unique port number? If so, then it is probably using STUN. If that is the case, then audio issues can arise (at sites with mote than one or two sets) if the audio ports are not set up correctly.

https://www.3cx.com/docs/manual/configuring-ip-phones/#h.ul2fzupi6t22/

You could try enabling PBX delivers audio, on a per extension basis, if it is not already done, to see if that offers a quick fix. Ideally, you may want to consider installing a 3CX SBC at the location with six sets.

https://www.3cx.com/docs/3cx-tunnel-session-border-controller/

 

[cobaltit]

So best guess is this setup was hacked together and not setup properly. For remote phones they should either say STUN or SBC. Local LAN would only apply if you had a site to site VPN tunnel from the phone location to your Azure setup. If you don't see any mention of SBC on the phones tab as @BrenttG mentions and you don't have a VPN then you'll want to start from scratch. Get a Raspberry Pi 3 (depending on the number of extensions) or spin up a VM if you have the infrastructure in place on-site. Factory reset the phones and use the PnP method to assign them to the extensions and that will resolve your audio issues.

 

[BrenttG]

oK, so i missed the part about them all being set to local, but that isnt a biggie, just switch them to Direct Stun, and stagger the ports properly as follows, ensuring PBX delivers audio is turned on for all extensions.

Phone 1
SIP: 5065
RTP start 14000
RTP end 14019

Phone 2
SIP: 5066
RTP start 14020
RTP end 14039

Phone 3
SIP: 5067
RTP start 14040
RTP end 14059

etc...

 

[rake-support]

Ok.. I have a lot more info for you guys.. and thanks so much for the ideas already..
1. We do have a VPN to Azure setup in the office where the 6 phones are.. They do not currently have any issues.

the 2 remote phones are on Direct Stun, with staggering ports.. and are the ones having the issues with not being able to hear any audio with dialing internal extensions.

I checked the box 'PBX Delivers Audio' on both external phones.. and it did not fix the issue, and one phone was no longer able to make outbound calls at all.. so I had to uncheck it for that phone. Anything else you can think of to check out?

 

[leejor]

Are the local SIP ports different, on each of those sets? i.e...one is 5060 and the other 5061? Setting to PBX Delivers Audio should not normally cause that problem. . In some cases, even with only two phones behind a router, the make/model of router can be an issue. There may also be a router setting (SIP ALG?), that is causing this. Are there other SIP devices, at that location ,not 3CX? Is the router one that also provides Voip service from a provider, (has RJ11 sockets?)

 

[Mark Phillips]

I'd be looking at the inbound/outbound rules on the relevant Azure Network Security Groups to ensure you are allowing the RTP traffic to pass.