Short answer
When a call connects but one or both sides hear nothing, the call's signaling got through and its audio didn't. If it happens on every call, it's usually the firewall or router in front of your PBX. If it happens on some calls, look at the phones, devices, and networks those calls have in common.
- Applies to
- Cloud SIP, Phone Numbers
- Works with
- Any SIP PBX or SBC
- Who can do this
- Whoever manages your PBX and your network
Check for a known incident first. If there is one, we're already working on it, and there's nothing to change on your side.
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What are you seeing?
- Every call connects with no audio, or audio only one way
- Only some calls, people, or devices have no audio
- You hear silence instead of ringing on outgoing calls
Every call connects with no audio, or audio only one way
If calls connect and the timer runs but one or both sides hear nothing, the call's signaling worked and its audio didn't arrive. Call audio travels separately from signaling, between your PBX (phone system) and Enfonica's two media addresses. When every call is affected, the cause is usually in the network in front of your PBX. These three checks cover it.
Your firewall isn't letting call audio through
Enfonica sends and receives call audio from two media addresses, on any UDP port. These are different from the signaling addresses that your PBX sends calls to. A firewall rule or port forward written for signaling alone lets calls connect, but with no audio.
Check
Look at what changed and at your firewall rules. This is the cause if the problem started with a new firewall, router, or site, or if your firewall rules name only 34.87.239.197 and 34.87.254.143.
Fix
In the firewall in front of your PBX, allow both media addresses, on all UDP ports, in both directions. This is a change in your own network.
| Traffic | IP addresses | Ports |
|---|---|---|
| Media (call audio) | 35.189.19.10635.189.6.179 | All UDP ports |
| Signaling | 34.87.239.19734.87.254.143 | 5060 (UDP), 5061 (TLS over TCP) |
Your PBX is telling Enfonica a private address for its audio
Each call's setup includes the address where your PBX wants to receive audio. If your PBX sits behind a router and gives its private address, such as 192.168.1.20, Enfonica's audio goes to an address it can't reach. SIP ALG, a router feature that rewrites SIP messages as they pass, can cause the same problem or garble the messages.
Check
Find the call in the Console, and open its SIP trace. Select the INVITE or 200 OK that your PBX sent, and look for the line that starts with c=IN IP4. This is the cause if the address on that line is a private one. Private addresses start with 10., 172.16. to 172.31., or 192.168.
Fix
In your PBX's network or NAT settings, set its public IP address (often called the external or public address). Then turn off SIP ALG on your router. Whoever manages your PBX and router can make both changes.
Your PBX is blocking some of Enfonica's addresses
Some PBXs, such as 3CX, add addresses to an IP blacklist automatically. If only some of Enfonica's addresses are blocked, calls can connect with audio missing.
Fix
Remove Enfonica's signaling and media addresses from your PBX's IP blacklist. Then add them to its IP whitelist so that they aren't blocked again.
Only some calls, people, or devices have no audio
When most calls are fine, the trunk and your firewall are working. Look for what the affected calls have in common, such as one caller, one user, one device, or one moment in the call.
One caller's phone or network
Check
Look at whose calls are affected. This is the cause if the problem follows one caller, and calls from other people to the same number have audio both ways.
Fix
Call the same number from a different phone. If that call is fine, the caller's handset or their network is the cause, and they're the one who can fix it.
One user's device, browser, or headset
Softphones, browser-based agent apps, and headsets each have their own microphone and audio settings. An update or a changed default device can silence one side.
Check
Look at whose calls are affected. This is the cause if the problem follows one user, wherever their calls go, and other users on the same PBX are fine.
Fix
Check the device's microphone and speaker settings, try another headset or browser, and restart the app. For browser-based contact center agents, the platform's own support team can check the agent's connection.
Audio stops after a hold or a transfer
Hold and transfer change where a call's audio goes partway through the call. Some phones and PBXs handle that change in ways the other side doesn't expect.
Check
Note when the audio stops. This is the cause if audio is fine until someone puts the call on hold or transfers it, and then one side goes quiet.
Fix
Check for a firmware update for the affected phones or PBX. Then send us an example call so that we can see exactly what was sent at that moment.
A short-lived fault on the network path
Check
Note when the problem happened. This is the cause if one-way audio affected a few calls in a short window, and calls made a few minutes later were fine.
Fix
Make a test call as soon as you notice the problem, and send us the affected calls with their exact times. With fresh examples, we can check each network the call passed through while the details are still available.
You hear silence instead of ringing on outgoing calls
On most outgoing calls, the ringing you hear comes from the network you're calling, as early audio. Enfonica passes it to your PBX with 183 Session Progress before the call is answered. When a call gets 180 Ringing instead, your PBX or dialer plays its own ringing tone.
Your PBX or dialer isn't playing early audio
Check
Open the call's SIP trace. This is the cause if Enfonica sends 183 Session Progress before the 200 OK that marks the answer, and audio works both ways after the call is answered.
Fix
Turn on early media (early audio) for the Enfonica trunk in your PBX or dialer. Its vendor can help with the setting, so show them the trace with the 183 Session Progress in it. If there's no audio after the answer either, see Every call connects with no audio.
How do I find where the audio stops?
The Console's SIP trace shows the call's signaling, including who offered audio, at which address, and whether the call was answered. It doesn't include the audio itself.
To see the audio, run a packet capture on your PBX during a test call, including RTP (the audio packets). Make sure that audio packets leave your PBX toward 35.189.19.106 or 35.189.6.179, and that packets from those addresses arrive. Audio that leaves and never comes back points to your firewall or router. Audio that arrives at your PBX but isn't heard points to the PBX or the phone.
If you're still stuck, send us two or three example calls with their times, and your capture if you have one.
What to send us
Include these and we can find the call straight away.
- The number that made the call and the number it called, in full international format (for example +61255501234).
- The date and time of the call, with your timezone.
- Whether the call was inbound or outbound.
- The call ID, if the Console shows the call.
- What happened: an error message, silence, a busy tone or a dropped call.
Our support team are telco specialists, backed by the engineers who run the network.
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