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What is Latency?

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Worried businesswoman using telephone at work
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Definition:

Latency has the reputation of being the enemy of VoIP. It is also called lag.

Latency is the time between the moment a voice packet is transmitted and the moment it reaches its destination. It of course leads to delayand finally to echo. It is caused by slow network links. This is what leads to echo.

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 taken for the packet to travel to and from the destination, back to the source. In fact, it is not the same packet that travels back, but an acknowledgement.

Latency is measured in milliseconds (ms) - thousandths of seconds. A latency of 150ms is barely noticeable so is acceptable. Higher than that, quality starts to suffer. When it gets higher than 300 ms, it becomes unacceptable.

Here are the effects of latency over voice quality:

  • It 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
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