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 in something. You can have latency on computer networks but also during voice communication. It's actually quite notorious and is a major problem in voice calls.

Latency is the time between the moment a voice packet is transmitted and the moment it reaches its destination, leading to delay and echo caused by slow network links. Latency is a major concern in VoIP communication when it comes to calling quality.

There are two ways latency is measured: one direction and round trip. One direction latency is the time taken for the packet to travel one way from the source to the destination. Round-trip latency is the time it takes for the packet 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.

Latency is measured in milliseconds (ms), which is thousandths of seconds. A latency of 20 ms is normal for IP calls and 150 ms is barely noticeable and therefore acceptable. However, any higher than that and the 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 or QoE.

Effects of Latency on Voice Calls

These are just a few of the negative effects of latency on call quality:

  • Slows down your phone conversations
  • Untimeliness can results in overlapping noises, with one speaker interrupting the other
  • Causes echo
  • Disturbs synchronization between voice and other data types, especially during video conferencing

How to Get Rid of Latency

This is a hard task and requires you to consider 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 do not have sufficient bandwidth. When the Internet connection is slow, data packets take more time to flow to and fro and this causes the communication 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, about which there's nothing you can do. However, if you are using VoIP apps that allow you to tweak with 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. You should try using a different telephone adapter or a different phone (if you are using an IP phone or any other VoIP-specific hardware). Your hub might also be a culprit. You may even want to check your headset, which very often causes latency.
  • If the system in place is converting the signal to or from analog or digital, that alone might contribute to the latency.
  • Buffering takes place both when audio data is being transferred and when there's a difference between the time of both events, and it can cause audio latency as well.