Latency—also called lag—is notorious for leading to poor quality VoIP calls. Latency is defined as the time it takes for one endpoint to send a packet to another. Latency can be measured in one direction, or in both, and is quantified in terms of milliseconds (ms). One-way latency is the time taken for a data packet to travel in one direction only and it is generally used to diagnose network problems.
On the other hand two-way latency measures the round trip time and this figure is used to calculate MOS scores. A high round-trip latency affects normal conversation between people since the data packets take longer to reach their destination, and also take longer for the acknowledgment to be sent back. Latency higher than 300 ms is generally unacceptable for reasonable conversations, especially for business organizations.
Latency is more of a problem for hosted VoIP since audio calls are real-time communications and even a slight delay is noticeable. Consistently high latency can slow down conversations and also lead to the dreaded 'talk over’ effect where one speaker interrupts the other unknowingly. Latency can also cause echoes making it hard for the listener to distinguish between spoken words. The situation can be especially aggravating if one or both of the callers have pronounced accents which is generally the case with international business calls.
High latency can cause severe problems in normal one-to-one calls but these issues can be exacerbated during multiparty video or conference calls. It can cause the audio to be out of sync with the video which can quickly derail project meetings. For all these reasons latency is taken very seriously and an organization should ensure low latency figures for high-quality audio calls.