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A primer

Mean Opinion Score (MOS)

What makes a good MOS? How can you improve yours? Keep reading to find out. Or, if you're looking for a telephony platform that can help your team members make crystal calls, book a product tour of Dialpad's AI-powered collaboration platform!


Your Mean Opinion Score (MOS) = the quality of experience your users are getting from your telecom service.

It doesn’t matter how many nifty features you offer or how cheap your product is—if you’re only providing low call quality phone service with jittering, latency, and dropped sessions, your customers will soon be scrambling to find another communications provider.

Here’s everything you need to know about MOS scores, how they’re calculated, and what they mean for your business.

What is a MOS score?

Mean Opinion Score is the industry standard measurement for Voice over Internet Protocol (VoIP) call quality. It measures the overall perceived quality of a call after the audio has been compressed using codecs and transmitted.

To calculate this, several critical metrics are used. These include jitter, latency, and packet loss. The MOS score is expressed as a numerical value, which represents the subjective experience of audio quality as registered by the human ear.

What makes a good MOS score?

MOS scores fall on a scale from 1.0 to 5.0, with a high score indicating good sound quality. A score of 3.5 would indicate that around half the users of a particular service have experienced low voice quality.

The majority of VoIP calls are rated somewhere in the MOS score range of 3.5 to 4.2. It’s unlikely for MOS scores to ever reach as high as 5.0, due largely to the human tendency to not award perfect ratings (and there’s no extra credit opportunities either). Therefore, a MOS score of 4.3—which would indicate excellent voice quality—is considered a good target to aim for.

The reality, however, is that over 50% of remote workers report audio quality as one of the biggest struggles of conferencing calling.

MOS score vs. VoIP call quality

MOS was originally developed as a metric for grading the quality of service (QOS) of traditional voice calls, but has since been adapted to Voice over IP calls.

MOS scores have been standardized by the International Telecommunications Union (ITU-T), with definitions provided on how to calculate VoIP MOS based on factors such as the codec used.

Each VoIP codec behaves differently, with some being uncompressed to increase quality and others using a compressed codec in order to reduce bandwidth usage.

How is MOS score calculated?

Originally, MOS scores were calculated using survey results from expert observers, much in the same way that a CSAT survey would be used to gauge overall customer satisfaction. Today, the more likely methodology for MOS testing is to use Objective Measurement Methods. These are algorithms that try to approximate the human experience.

The most commonly used codec for VoIP calls is the G.711 codec, which has a maximum MOS score of 4.4. The table below illustrates how MOS scores translate to call quality, according to limit values from the ITU-T standards:

MOS Score

Call Quality

Over 4.34


4.03 - 4.34


3.6 - 4.03


3.1 - 3.6


Below 3.1


The Mean Opinion Score formula is as follows:

Mos formula

Where R are the individual ratings for a given stimulus by N subjects

Where can MOS be used?

Mean Opinion Scores can be used anywhere that human subjective experience is useful. A MOS value is often applied to judge how well real-world phenomena have been replicated digitally.

This could be in instances of static image compression, audio codecs, video codecs, and more. All these places can have varying levels of success depending on the circumstances surrounding them, so MOS is helpful in determining the effectiveness of the results.

MOS is also regularly used to rate the success of streaming sessions, where communications quality is affected by network effects.

How Dialpad delivers high MOS scores

One of the key focuses of Dialpad has always been call quality. Whether it’s a phone call, a video conference, or a contact center interaction, we understand that getting call quality right is essential in providing a great user experience.

We’re so used to excellent quality when making cell phone calls that we often take it for granted—underestimating just how difficult it can be to achieve.

Take video meetings, for example. To access most video and audio conferencing sessions, each connection is made via internet protocol (IP) to a common address in the cloud. An app or browser is used to log on and establish one instance of an interaction in that meeting room.

This means that each route of access to that meeting room is subject to the network infrastructure supporting it, including routers and more. If that network is running a lot of other apps, or the voice or video traffic is prioritized for another reason, then the call quality can go down real quick.

This could be in the form of jitter caused by network latency, propagation delay, RO packetization delay, or even dropped calls and sessions. (At least, that’s true of most providers.)

Thankfully, Dialpad uses a dual-cloud architecture model that helps to circumvent these problems entirely. This means that the voice aspect of calls is entirely separated from the business side of proceedings.

With Dialpad, all the behind-the-scenes features of a call are handled in the Google Cloud Platform (GCP). Apps, integrations, analytics, call routing instructions, and user info; all this and more exists in the software cloud, where top-grade security keeps it safe, and running reliably.

Not only that, but existing in the cloud makes it easy for Dialpad to be upgraded with new features and facilitates near-infinite scalability as your business demands it.

All call traffic, on the other hand, is routed through a proprietary global telephone network. This has been built out at Dialpad from its inception; it’s grown as we’ve grown. It’s made up of carrier connections to telephony engines (TEs) based in 12 data centers all across the globe.

These TEs exist solely to transmit voice traffic around the world, so deprioritizing call quality is never a concern. Our TEs operate at a very low capacity and include failover, meaning that network outages, or other factors that could cause poor call quality, are also eliminated.

All this combined means that Dialpad offers crystal clear audio and video quality, without jitter, latency, or the risk of dropping calls. The voice signal is unfettered and unique to each user on the Dialpad call or meeting. This leads to users reporting consistently high MOS scores for every interaction through Dialpad.

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