What Is VoIP Latency, and How Can It Be Reduced?

Dealing with echos and overlapping noises

Worried businesswoman using telephone at work
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Latency is a delay or lag. You can have latency on computer networks and during voice communication. It's actually quite notorious and is a major problem in voice calls.

Specifically, latency in VoIP (voice over internet protocol) calling is the time between the moment a voice packet is transmitted and the moment it reaches its destination. High latency translates to delay and echo caused by slow network links. Latency is a major concern in VoIP communication when it comes to calling quality.

Latency is measured in two ways:

  • One-direction latency is the time a packet takes to travel one way from the source to the destination.
  • Round-trip latency is the time a packet takes to travel to and from the destination, back to the source. In fact, it's not the same packet that travels back, but an acknowledgment.

Measuring Latency

Latency is measured in milliseconds (ms), which is thousandths of seconds. A latency of 20 ms is normal for VoIP calls; a latency of 150 ms is barely noticeable and therefore acceptable. Any higher than that, however, and quality starts to diminish; 300 ms or higher, and it becomes completely unacceptable.

Telephone latency is sometimes called mouth-to-ear delay, and internet-related audio latency also goes by the term quality of experience (QoE).

Effects of Latency on Voice Calls

Just a few of the negative effects of latency on call quality include:

  • Slow and interrupted phone conversations.
  • Overlapping noises, with one speaker interrupting the other.
  • Echo.
  • Disturbed synchronization between voice and other data types, especially during video conferencing.

How to Get Rid of Latency

Eradicating latency is difficult and involves several factors, many of which are beyond your control. For instance, you do not choose which codecs your service provider uses.

Here are the factors that tend to cause VoIP latency:

  • You lack sufficient bandwidth. When an internet connection is slow, data packets take more time to flow to and fro. This causes quality to suffer. Often, the packets arrive in the wrong order, which makes reassembly impossible unless the order is restored. This is one of the disadvantages of packet switching, which VoIP uses.
  • Your firewall might be blocking traffic. Checkpoints are always a bottleneck, so make sure you allow clearance for your VoIP apps within the firewall software.
  • The wrong codecs are being used. Codecs are programs used to encode voice signals into digital data for transmission over the network, and your provider might be using the wrong one. You can't do anything about that; however, if you're using a VoIP app that allows you to tweak codecs, try changing them.
  • You're using old hardware. Old hardware with new software or new networks might not work that well, and delay and latency are often a result. Try using a different telephone adapter or phone (if you are using an IP phone or any other VoIP-specific hardware). Your hub also might be a culprit. Headsets often cause latency, too.
  • Your system might be converting the signal to or from analog or digital.
  • Buffering is causing audio latency. Buffering occurs when audio data is being transferred and when there's a difference between the time of transmission and reception.