What Is VoIP Latency, and Can It Be Reduced?

Dealing with echoes and overlapping noises in VoIP calls

Worried businesswoman using telephone at work and experiencing latency in her VoIP call

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Latency is a delay or lag. Latency occurs on computer networks and during voice communication. Latency in VoIP (Voice over Internet Protocol) calling is the time between when a voice packet is transmitted and the moment it reaches its destination. High latency translates to a delay and echo caused by slow network links. Latency is a major concern in VoIP communication when it comes to calling quality.

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

How to Measure 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 even 150 ms is barely noticeable and therefore acceptable. Any higher than that, however, and quality starts to diminish. At 300 ms or higher, latency becomes completely unacceptable.

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. (The same packet doesn't travel back, but an acknowledgment does.)

Effects of Latency on Voice Calls

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

Latency Causes and Fixes

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 cause VoIP latency and what, if anything, can be done to fix it.

The Connection Doesn't Have Sufficient Bandwidth

When an internet connection is slow and lacks sufficient bandwidth, data packets take more time to flow across the internet. This causes quality to suffer. Often, the packets arrive in the wrong order, which makes reassembly impossible unless the order is restored.

The Firewall Blocks Traffic

Checkpoints are always a bottleneck, so allow clearance for your VoIP apps within the firewall software.

The Wrong Codecs Are Used

Codecs are programs used to encode voice signals into digital data for transmission over the network. Your provider may use the wrong one. You can't do anything about that; however, if you use a VoIP app that allows you to tweak codecs, change them.

Old Hardware Is Used

Old hardware with new software or new networks might not work very well, and delay and latency are often a result. Use a different telephone adapter or phone (if you use an IP phone or any other VoIP-specific hardware). Your hub also might be a culprit. Headsets often cause latency, as well.

The Signal Doesn't Convert Correctly

Your system may 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.