1) NAT Issues
This is a very common problem with the SIP protocol where the incoming packets do not reach your device, causing no incoming audio. In some cases the packets from the device also do not reach the other side, causing the other side not to hear anything.
The main culprit is the way NAT networks (like your typical home or office router) distribute one internet connection to multiple pc's and phones. To make this possible, they use a method called port mapping.
Without going into details (you can read more here if you want), it causes the ports used by VoIP programs to change in a mostly unpredictable way and can often result in one-way or no audio, failed incoming calls, automatic hangup after 30s and more.
Open the Command Prompt (CMD)
Do a traceroute e.g tracert google.co.za
If the first 2 hops are of the local IP address then there is double natting
In a Mac Book
Open the Terminal
Do the traceroute
2) SIP ALG or firewall on the router
- SIP ALG (Also called SIP PASS THROUGH or SIP HELPER) was invented to get around NAT problems by rewriting some packets.
- Unfortunately, SIP is rather complicated and most SIP ALG implementations are horribly broken. (Netgear, Dlink, Zyxel).
- If you experience missing audio, failing registrations, failed calls, failing video calls, or failed transfer, please verify that your router does NOT use SIP ALG and disable SIP ALG if it does.
- If you are unable to change the router configuration, try using TLS encryption (if the SIP server supports it) to encrypt the traffic and stop the router from tampering with the packets.
3) An issue with the headset, phone, audio card, or audio driver
- If the issue happens only on some WiFi and 3G/4G networks or to some destinations, the headset, phone, audio card or audio driver are most likely not to blame.
- Please refer to the NAT-related issues above instead.
- If only the microphone does not seem to be working, please ensure the call is not accidentally muted. (This will be more for your Softphones e.g Webphone or Voys App)
Mac or Windows (Webphone Related)
- First, make sure your audio devices are configured properly in Webphone/softphone
- If you are using a laptop and expect to hear the sounds come out of the speakers, check to be sure that no audio headset (wired or Bluetooth) is currently connected.
- Go to Settings -> Devices
- Make sure the input device and output device are selected properly. Try the microphone and speaker with the built-in test, and check to see if the green bar is moving
4. Misconfigured port forwarding.
- Some users block all firewall ports and only open or forward the default SIP port 5060 as shown in this tutorial.
- This will break horribly in most cases, if you really want to go this path, keep in mind that the RTP (media packets) will not always use the same port. Typically they will start at a port and for each extra stream (video for example or a second call) will open a new higher port.
- We cannot help you with this setup, please consult with a network engineer/IT personnel familiar with SIP and port forwarding.
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