Solving VoIP one way audio

Solve One Way Audio-Step by Step

One way audio where one side or one party can hear the other, but not reverse, is typically indicative of something stopping either the outbound or inbound audio from reaching the receiving party.   One way audio can be caused by network issues; NAT (Network Address Translation) issues or firewalls, so finding the cause will require simplification of the connection by elimination of some equipment, then testing.  Once the problem device is found its pretty much initiating changes that resolve the issue.  here's how to troubleshoot one-way audio.

Step One- Check your equipment.

The first thing that you need to eliminate is a faulty phone, handset earpiece or a headset on a softphone.  To do the do the following:

• Softphone- Check that you have audio in both the earpiece and microphone.  Verify that your microphone is connected properly.  Try using Windows Sound Recorder (or another application) as a check and make sure that the microphone is selected as the input device in your Control Panel. 
  • Make a test call to yourself and start speaking to verify the microphone meter is showing movement.
• Regular phone- Sometimes the best testing can be achieved using a simple corded phone.  Connect one that is working correctly, both the mouth piece and ear piece.
• IP Phone- Make sure the phone is functioning correctly.

Step Two- Simplify the connection.

Now that you know the equipment (phone/softphone with headset) are functioning correctly it's time to simplify the LAN (Local Area Connection) and the way the VoIP device is connected.  The first step in one way audio troubleshooting is to simplyfy the connections.  This allows you to identify the actual cause of the VoIP one-way audio. Do the following:

• Connect the VoIP ATA, IP Phone, or PC with softphone directly to the modem device.  Make sure you get registered and obtain a valid IP address.  In many cases this could be a public IP address.  Make a test call.  If one way audio still exists check to see if you have a public or private (192.168.1.xxx) IP address. 
  • Public IP- Call your VoIP provider.  If you are getting one-way audio with a public IP address, there is an issue with the way the VoIP provider is handling the call.
  • Private IP- If you are getting a private IP address from your modem it is acting as a NAT router and in this case preventing the audio from making it to the ATA.  Check for SPI (Statefull Packet Inspection) or any firewall settings that may be the cause.  Turn them off and retest.
    • If you are getting a private IP address and not able to get two way audio, you will want to set the modem to bridge mode and allow your router to act as the only NAT router on the network.  Instructions to do the can be found at Bridging a DSL modem.

Step Three- Reconfigure your LAN network.

After completing step two you should have achieved a good two-way audio call.   Now you will want to configure your network for your VoIP to work correctly.  This typically might include eliminating a second layer of NAT from your network design. 

• DSL/Cable modem as router-  More and more modems are acting as routers (both hard wired and wireless), firewalls and handing out DHCP.  If you have to keep your modem as the primary NAT router (perhaps you need the wireless capabilities) then you will need to eliminate any secondary router from creating a second layer of NAT.
  • Use a switch on the LAN in place of a router or disable DHCP on the second router.
• Bridge the modem-  Set the modem to bridge mode and allow the public IP address to sit on the WAN side of your router.  This may require placing PPPoE settings in your router.  Then this router handles the NAT translations.
• Two routers-  If you have two routers, perhaps one wired and the other wireless you will need to configure these routers correctly for best network practice.  Connecting a wireless router to another router.
• Port forwarding-  Configuring port forwarding on your router can be beneficial and resolve many NAT related one-way audio issues.  After completing the best practices with your network you might use port forwarding as a way to make sure that the router knows where to send incoming VoIP audio.