Ringback/progress tone playing once then silence

[richiewhite]

Hey team, I'm trying to get more information from the end customer, but I figured I'd try here before raising a support case once I've got everything I need. I have a user complaining that when calling outbound they are hearing a single ring/progress tone, and then silence. This continues until the recipient answers, and then they hear normal audio.

They're using the PWA in Microsoft Edge, and have a Jabra 390 Link dongle, but haven't confirmed what the actual headset is. I've tried to reproduce this myself on their own system, and can't reproduce it at all. In a PCAP I see that calls to mobile numbers are being responded to with early media that's originating at the mobile carrier, and when capturing the messaging while I get him to reproduce the issue I see early media traversing between the SIP trunk and the WebRTC proxy just fine. I've also set ENABLEEARLYMEDIA to 0 to see if it is an early media issue, but this hasn't resolved it. They also report that this is happening on internal calls.

They're reporting that they have no issues using the mobile app, but their entire office is seeing this issue using the PWA, so I'm leaning network issue.

As always with end users I'm having some trouble trying to convice them to go through any other testing like changing the audio device to their PC speaker to rule things out, or to capture from webrtc-internal so I can check what audio is actually being received by the browser.

Has anyone else run into a similar issue?

 

[KyriacosS_3CX]

Can you advice what the 3CX PBX setup is like? Version, install type etc. Also how the customers end points reach the PBX, and if the trunk provider is a supported one? As you say, something in the network, or some security suite on the computers might be the most likely cause, but a fuller picture is needed.

(Hint: using the correct system key in the forum helps )

 

[KyriacosS_3CX]

And, in case it does help, here is a big blob of AI generated suggestions (it agrees with you for the most part) -

The issue you're describing – a single ring/progress tone followed by silence until the recipient answers, affecting the entire office using the PWA in Microsoft Edge, and also occurring on internal calls – is quite specific. The fact that early media is seen traversing between the SIP trunk and the WebRTC proxy, and that the mobile app works fine, strongly points to a client-side issue (browser, headset, or local network) rather than a core PBX or SIP trunk problem. The internal call issue further isolates it to the path between the 3CX WebRTC proxy and the client.

Here are some focused troubleshooting steps, prioritizing those that can help pinpoint the exact cause, especially given the "entire office" scope:

1. Gather webrtc-internal Logs (Critical): You mentioned difficulty getting end-users to perform this, but it's the most vital step. These logs provide a detailed view of what audio the browser is actually receiving and processing. It will confirm if the early media RTP packets are even reaching the browser and if there are any errors in decoding or rendering them.
   
   • How to get them: Ask an affected user to open a new tab in Microsoft Edge, navigate to edge://webrtc-internal, and then reproduce the issue by making an outbound call. After the call, save the logs from this page.
2. Test with PC's Built-in Speakers/Microphone (Critical): Again, you noted this is a challenge, but it's essential to rule out the Jabra headset/dongle. If the problem disappears when using the PC's native audio devices, the issue lies with the headset, its drivers, or its interaction with Edge/PWA.
3. Client-Side Network Inspection (for "entire office" issue): Since this affects everyone in the office using the PWA, a common network-level interference on the client side is a strong suspect.
   
   • Firewall/Proxy/Security Software: Corporate firewalls, web proxies, or endpoint security software (antivirus, DLP) can interfere with WebRTC RTP streams.
     • RTP Port Range: Ensure that the RTP port range (default 9000-10999) is fully open bidirectionally between the client machines and the 3CX PBX. The 3CX system uses this range for media traffic.
     • Deep Packet Inspection/SIP ALG: Check if any network devices on the client side have deep packet inspection or SIP ALG features enabled that might be interfering with WebRTC traffic.
     • External Network Test: If possible, have an affected user test the PWA from a network outside the corporate environment (e.g., working from home). If the issue does not occur there, it strongly indicates an internal network problem.
   • QoS (Quality of Service): Misconfigured QoS policies could be dropping or deprioritizing early media RTP packets, leading to the silence you're hearing.
4. Browser-Specific Checks (Microsoft Edge PWA):
   
   • Browser Extensions: Ask an affected user to temporarily disable all browser extensions in Microsoft Edge and re-test. An extension could be conflicting with WebRTC audio.
   • Browser Cache/Data: Clear the browser cache and site data specifically for the 3CX PWA.
   • Browser Permissions: Verify that the PWA has explicit permissions for microphone and speaker access in Edge settings.
   • Update Edge: Ensure Microsoft Edge is updated to its latest stable version.
   • Test with another Chromium-based browser: Try reproducing the issue in Google Chrome (which shares the same rendering engine as Edge). If the issue persists, it might be a broader Chromium-related problem; if not, it's more specific to Edge.
5. Jabra Headset/Dongle:
   
   • Drivers/Firmware: Ensure the Jabra 390 Link dongle and the connected headset have the latest drivers and firmware installed.
   • Jabra Direct/Software: If Jabra Direct or similar software is installed, check its settings for any audio processing or integration options that might be causing interference.

The key to resolving this will likely be the webrtc-internal logs and testing with the PC's native audio devices, as these will provide direct insight into the audio path at the client endpoint.

 

[richiewhite]

Thanks, unfortunately this is a different Partner's system that I'm involved with supporting so I'm unable to use the correct key in the forum with my own account! The appropriate partner would raise support in their portal if it came to that.

The PBX is running 1121, though it was updated from Update 7 to see if we could resolve with an update/service restart. Install is cloud (AWS). The trunk provider is supported using the built in template.It's 4SC Pro, with 14 user extensions configured.

There is a double NAT situation going on, there is a Mikrotik firewall managed by the partner themselves connecting to the primary internet connection, but the end-customer themselves has a TP-Link setup that's unknown to me right now that's the only device the firewall is seeing. Given the impact across the office but only impacting the webclient/PWA, not the mobile app, and with us unable to reproduce the issue elsewhere using the webclient, I'm leaning toward something on that TP-Link kit being the cause.

 

[KyriacosS_3CX]

While you might need a ticket, as the easiest way forward - do a packet capture and look + listen to the streams, to see what exactly is going on - your SIP provider might also want to take a look.

 

[Kevin Attard Compagno]

Also, please keep in mind that:

double-NAT and VoIP are NOT friends!