MOS VoIP

What is the MOS in VoIP?

Mean opinion (MOS) is a measure or metric used to measure VoIP call quality or audio quality. Instead of describing your VoIP call quality in vague terms, like good or bad, VoIP MOS VoIP gives you an objective measure of voice quality.

Generally speaking, the MOS is between 1 to 5, where 5 means the best VoIP call quality and 1 means a low quality of service. These scores are more straightforward to compare than subjective tests and comments like “I’m having a lot of choppy voice calls.”

Measuring voice quality with MOS is also helpful when comparing two different VoIP call providers. For example, you might find that a business VoIP call service has consistently better MOS numbers than a free service. In that case, choosing the service with the better conversational quality (i.e., higher MOS number) makes sense.

Expert's note

When you have your conversational quality on a VoIP call suffers, run a MOS check.

This number will help you to have a more informed conversation with your technical support department.

Now let’s take a deeper look at the mean opinion score (MOS) and how this quality measure is calculated.

Measurement of MOS

In practice, most people use software to calculate a MOS. So you don’t need to open Excel or use a calculator to come up with the metric manually. That said, it is helpful to know how a MOS is calculated to understand it better.

The first step in calculating a MOS is gathering the following data points. Note that you can use network performance monitoring software to gather this numerical measure data more quickly.

  • propagation delay – Measure the time required for an individual digital signal to travel across the entire network. More complex networks with routers, switches, and other delays tend to have a higher propagation delay. Put another way, this metric measures the one-way delay for data to travel from your computer to the person you are calling.
  • packetization delay – This time metric represents the time needed to convert information like the sound of your conversation into digital information (i.e., voice packets) and ultimately decode it at the other end. Note that using a non-compressed codec can have a lower packetization delay.
  • jitter buffer – The digital data representing your call do not always arrive as expected. As a result, delays are needed to compensate for differences in packet arrival time. When the percentage of packet loss goes up, the voice packets have to be resent. This causes more processing delays and a buffering delay. Ultimately, jitter buffer problems translate into VoIP (voice over Internet protocol) issues.
Metrics vector

As you start to learn more about network performance monitoring, there are a few more terms you may want to know to diagnose VoIP issues.

  • RTP packet – Real-time protocol (RTP) moves the voice information or voice packets across the network. Various factors like packet loss, jitter and latency impact whether RTP packet transmissions operate smoothly. Understanding RTP packet performance is vital to understanding VoIP statistics properly.
  • packet counts – This metric is helpful because it puts packet loss into context. For example, if your VoIP call has 50 packets per second and you are losing 5 packets per second, you lose a significant portion of the call to packet drop. The packet counts involved vary depending on the VoIP codec used.
  • packet loss simulation – Before you start a VoIP call, you can use packet loss simulation to estimate the voice quality of the call. For mission-critical applications like important business calls, it is wise to use packet loss simulation to diagnose problems.

What are the benefits of a good MOS for VoIP?

Your VoIP connection needs to maintain a good MOS to make the most of IP telephony.
Generally speaking, an acceptable score is 4.3 to 5. However, voice call quality may be considered “ok” when your mean opinion score falls to 3.6. If you are seeing individual scores fall below 3.6, your conversation might start to sound like a robot voice.

Note that it is helpful to measure your MOS several times throughout the day to determine your average score. By taking several measures, you may find times when your Internet connection has lower bandwidth usage.

Using MOS to describe the quality of your voice over IP is much better than vague descriptions like “robot voice” or “excellent quality.” When you have multiple Mean opinion scores available, you can better discuss ways to avoid quality issues on your calls with network engineers.

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How to increase your MOS results?

Nobody looks forward to poor VoIP quality. Before you switch back to making traditional voice calls, don’t give up hope. There are a few simple ways you can get better audio signals.

Seek assistance from your Internet service provider

Start by asking your ISP about ways to avoid network congestion. They may tell you of ways to improve call quality across your entire network. To illustrate the problems you face, offer to run a ping tool while you are on the call with technical support. In a more extensive company network, IT may use network device monitoring tools to diagnose the cause of VoIP health problems. In some situations, a network assessment can help to pinpoint the cause of network slowdowns.

You might be told that the entire network is experiencing network errors due to emergency maintenance. In that situation, you might be out of luck. Consider rescheduling your calls to another time so that you can avoid poor quality on your calls. Otherwise, ask your Internet service provider for tips on better managing the network traffic in your location to prioritize phone calls.

Expert's note

Make sure to discuss network latency with your Internet service provider if they do not bring it up.

Your Internet service provider may have further tips based on their experience with network monitoring.

Ask your VoIP service provider for advice

A high-performance VoIP network is designed to avoid choppy calls, but they still happen sometimes. Assuming you are working with a professional VoIP provider that uses a fast codec for VoIP calls, you can run a few tests. They might run quality of experience (also known as QoE for VoIP) testing. This measure considers the view of you as the human user making voice calls. In addition, they may run a mean opinion score (MOS) to understand your digital signal situation better.

After gathering this information, ask your VoIP service provider what can be done to avoid further voice quality degradation. They may suggest running a firmware update on your modem or router. In addition, switching to a different microphone can help to reduce background noise during phone calls. Generally speaking, a residential VoIP provider plan may have less capacity to improve your voice signal quality.

To summarize, there are a few ways you can improve your VoIP MOS and have better calls.

  • bandwidth conservation – Turn off other devices and applications before you make a call so that there is no impediment to VoIP traffic.
  • codec speed – Ask your VoIP service provider if you can make a codec speed change. The default values in codec settings are not ideal in every situation.
  • high-fidelity audio – Consider using a noise-cancelling headset during calls because this can help you to tune out background noise.
VoIP illustration

As you make progress on improving your voice quality, there are a few more terms you may encounter.

  • rating factor – This refers to a technical formula called the E model. The E model is written as R = Ro – Is – Id – Ie + A + W. Each variable in the model is a separate rating factor that ultimately describes the quality of the call.
  • advantage factor – A variable in the E model represents convenience to the end-user. The model assumes that people may tolerate lower voice quality for convenience (i.e., the willingness of many people to tolerate quality issues on a cell phone call).
  • base factor – It is the “Ro” in the E model. It refers to the background noise effects which can impact the quality of the factor.

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Frequently asked questions

What is the MOS value in VoIP?

Mean opinion score (MOS) is a measure or metric used to measure VoIP call quality. The MOS is between 1 to 5, where 5 means the best VoIP call quality and 1 means a low quality of service.

What makes up MOS?

MOS is based on several factors, including propagation delay, packetization delay, and jitter buffer. A well-configured VoIP server is less likely to have problems, but they can strike any VoIP service.

How do you measure MOS?

While it is possible to measure MOS manually, few people do it that way. If you are trying to improve the performance of VoIP desk phones in a large company, use network tools instead. Specialized network tools can also make it easy to measure latency on the network.

What is a good MOS for VoIP?

A good MOS for VoIP is between 4.3 to 5. When possible, make an effort to get your MOS closer to 5.

What is a good internet speed for VoIP?

Most experts suggest an Internet speed of 5 megabits download and upload for modern VoIP. This speed also makes it possible to browse the web and send an email while making a VoIP call. When you share an Internet connection with many other people (e.g., 100 – 999 users in a large building), buy the fastest Internet service you can afford.

What are the benefits of MOS?

MOS is a helpful diagnostic tool to improve the performance of VoIP calls. Rather than simply describing a VoIP call as good or bad, you can get an objective score up to 5. When used alongside other network metrics like latency, MOS can speed up fixing VoIP quality issues.

What affects your test VoIP MOS?

Several main factors impact your MOS: your VoIP service provider, Internet service provider, and network. To increase your test MOS and enjoy better VoIP calls, work on optimizing each MOS factor.

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