TeleDynamics Think Tank

How to troubleshoot problems arising from blocked ports, ACLs, firewalls, NAT, and more

For networking professionals, one of the most difficult things to deal with is troubleshooting VoIP issues, because the troubleshooting process for VoIP is not always intuitive. Answers to the questions, “What could be wrong?” and “What should I check first?” are not always readily apparent.

To aid your troubleshooting and allow you to take some meaningful actions before reaching out to your telco or vendor help desk, we’ve listed the most common VoIP problems you may face, as well as their causes and solutions. 

Are you hearing both sides?

By Kate Clavet, Marketing Specialist, Grandstream Networks

The very technology that makes VoIP so efficient can also indirectly cause one-way audio issues.

VoIP stands for Voice over Internet Protocol (VoIP), indicating that the communication travels over the internet in little packets using RTP (Real-Time Transport Protocol). Since the packets are traveling through the internet, they must pass through firewalls and network address translation (NAT). Due to the tricky nature of firewalls, a common complaint of customers and installers alike is that either the caller or callee cannot hear the other party. Although this is a common inquiry and topic for support tickets, it is also rather easy to fix.

If you deal with Voice over IP (VoIP), you must have come across this scenario at one time or another: A user complains that when they answer their phone, the caller can’t hear them, even though they can hear the calling party. Or, it may be that neither party can hear the other and there is just silence on the line.

This is the classic case of one-way or no-way audio, where a voice call is successfully completed, but either the voice packets only successfully travel in one direction, or neither end successfully receives voice packets. It may be difficult to understand why this happens, especially since the phone does ring, both physically for the called party and via the ring-back tone for the calling party. It seems counterintuitive that the transmission of voice packets could be unsuccessful if the call was successfully set up.

This is a scenario that comes up a lot on our tech support calls at TeleDynamics. Here we list four of the most common culprits of this issue and suggestions for how to tackle them.