What Is VoIP Latency, and Can It Be Reduced?

Latency is a delay or lag that occurs on computer networks. In voice communication or VoIP (Voice over Internet Protocol), latency refers to the time between when a voice packet is transmitted and when it reaches its destination. High latency translates to a delay or echo caused by slow network links.

How to Measure Latency

Latency is measured in milliseconds (ms), which are thousandths of a second. 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. At 300 ms or higher, latency becomes 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.

1. Insufficient 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.

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

3. Wrong codecs. 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.

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 Outdated hardware.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

5. Faulty signal conversion. Your system may be converting the signal to or from analog or digital.

6. Buffering. Buffering occurs when audio data is transferred and when there's a difference between the time of transmission and reception.