MOS 101: Call Quality in VoIP

August 22, 2018
Category: Business Phone Service, VoIP

The mean opinion score (MOS) has been a measure of telephone voice quality for decades. It was originally used to assess users’ subjective opinions of their call quality. As telephone technology expanded into the digital space, MOS adapted to test the quality of Voice over Internet Protocol (VoIP), including transmission quality as well as issues like voice degradation and performance.

As VoIP continues to increase in popularity, MOS scores are becoming essential to ensuring client satisfaction for continued network growth. Let’s take a quick look at how MOS scores work and what they mean for your business.

MOS 101: Call Quality in VoIP

How MOS Scores Are Measured

Once upon a time, MOS scores placed emphasis on the word “opinion” in that they used to be very subjective. After all, one person’s “great” could be another’s “terrible”, so there was no standardized way of defining which was more correct.

Now, fortunately, MOS testing is much more objective; it is defined in the ITU-T PESQ P.862 standard. In other words, MOS testing is based on a formula. In order to collect the most accurate results, VoIP equipment needs to be loaded with speech-like signals that are optimized to avoid unpredictable or unreliable results.

Notably, human involvement is still the most effective (but not always the most practical) way to curate an MOS score. This is done by calculating the average score across all participants from 0–5, with 5 representing excellent call quality and 0 being incomprehensible.

On the other hand, tests can rely on algorithms that focus on modern response time, codec speed, and complex tests to predict how voice quality would be perceived by the human ear. These types of tests may not be the most effective, but they are more practical and scalable than tests involving actual users.

MOS Score Factors

Once the data from the MOS tests have been gathered, you’ll want to incorporate the R-factors into the final score calculation. R-factors can degrade call quality but aren’t due to network error; they include:

  • Propagation delay
  • Packetization delay
  • Jitter buffer
  • The final MOS score reports on the following three aspects of the VoIP call:
  • Listening quality
  • Transmission quality
  • Conversational quality

Depending on what you’re trying to measure with an MOS score, you can adjust tests to focus on one or all of the above.

Lastly, testing MOS on VoIP systems comes with its own set of challenges to consider, including the following:

  • Hardware
  • Bandwidth
  • Jitter
  • Latency
  • Packet loss
  • Codec version

With a holistic assessment of all of these factors, you’ll have a much more accurate picture of how your VoIP system performs in terms of quality.

MOS Scores and Your Business

According to the Customer Experience Foundation, 79% of consumers have had issues with poor VoIP service. If your MOS scores are low, it’s time to improve your network before it gets worse—and customers abandon you in search of a better quality VoIP system.

Thankfully, with MOS scores, you’re able to pinpoint the exact problem with your network. With the data generated from the test, networking professionals will be able to troubleshoot the in-line appliance that is causing the issues—which means you’ll be able to raise your score and improve your systems.

Founded in 2007, Datastream Communications is a hosted VoIP provider that offers complete cloud phone systems and phone numbers to businesses within the Mid-Atlantic region. Contact us today to learn more about MOS scores and how they can improve your VoIP system.

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