MOS= Mean Opinion Score for VoIP Testing

Mean Opinion Score or MOS assigns a score (1.0-5.0) to indicate Voice over IP call quality after it is transmitted and compressed using codecs.  The result is a measurement that is useful in predicting VoIP call quality.  For instance, if a VoIP Service Provider’s average MOS score is 3.5, then an estimated 50% of users will complain of experiencing poor voice quality.  As VoIP Service Providers and Internet connectivity become more reliable we will see average MOS scores increase, however currently, on average, VoIP calls fall in the 3.5-4.2 MOS range.  A 5.0 score is generally unheard of, as it is considered perfect and has been compared to in-person, face-to-face conversations (though anyone using HD voice (G.729 codec) would argue that their MOS score must be a 5.0- it’s that clear). 

The following chart provides MOS comparison values and can be used as a simple tool for judging voice quality.

Maximum for G.711 codec 4.4
Very Good 4.3-5.0
Good 4.0-4.3
Just Ok 3.6-4.0
Bad 3.1-3.6
Very Bad 2.6-3.1
Not Recommended 1.0-2.6

What affects VoIP MOS scores?

MOS is a relative scale and there are many factors that can affect voice quality such as bandwidth, codec, hardware, jitter, latency, and packet loss.

Propagation Delay:  the time it takes for a digital signal to travel from start to finish over the entire network, including traveling through routers, switches, and firewalls.  The greater the distance, the greater the propagation delay.  

Packetization Delay:  the time it takes to digitize the signal based on the codec used as it’s sent over the internet and decoded at the end.  A more compressed codec like G.729 has a higher packetization delay than a non-compressed codec, like G.711.

Jitter Buffer:  in VoIP, a jitter buffer is an area where voice packets are collected and stored and then sent to a processor at more even intervals, basically intentionally delaying packets so that the received voice is heard with more clarity and less distortion.

Which Providers Offer High MOS Scores?

We can only speak for ourselves. ACC Telecom, a VoIP Service Provider, has a boastful 2016 YTD MOS score of >4.0 99% of the time.  Click here to learn more about Business VoIP solutions.

ACC Telecom specializes in business phone systems, Cloud PBX, VoIP / SIP Trunking service, IP surveillance camera systems, low-voltage cabling, overhead paging systems, and carrier services for businesses throughout Maryland, Washington DC, and Virginia.  Contact us to schedule your free consultation. 

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