Mean Opinion Score and Metrics

Listening MOS

Listening MOS is a prediction of the wideband Listening Quality (MOS-LQ)) of the audio stream that is played to the user. This value takes into consideration the audio fidelity and distortion and speech and noise levels, and from this data predicts how a large group of users would rate the quality of the audio they hear.

The Listening MOS varies depending on:

• The codec used

• A wideband or narrowband codec

• The characteristics of the audio capture device used by the person speaking (person sending the audio).

• Any transcoding or mixing that occurred

• Defects from packet loss or packet loss concealment

• The speech level and background noise of the person speaking (person sending the audio)

Due to the large number of factors that influence this value, it is most useful to view the Listening MOS statistically rather than by using a single call.

Sending MOS

Sending MOS is a prediction of the wideband Listening Quality Mean Opinion Score (MOS-LQ) of the audio stream that is being sent from the user. This value takes into consideration the speech and noise levels of the user along with any distortions, and from this data predicts how a large group of users would rate the audio quality they hear.

The Sending MOS varies depending on the:

• Users audio capture device characteristics.

• Speech level and background noise of the users device.

Due to the large number of factors that influence this value, it is most useful to view the Sending MOS statistically rather than by using a single value.

Network MOS

Network MOS is a prediction of the wideband Listening Quality Mean Opinion Score (MOS-LQ) of audio that is played to the user. This value takes into consideration only network factors such as codec used, packet loss, packet reorder, packet errors and jitter.

The difference between Network MOS and Listening MOS is that the Network MOS considers only the impact of the network on the listening quality, whereas Listening MOS also considers the payload (speech level, noise level, etc). This makes Network MOS useful for identifying network conditions impacting the audio quality being delivered.

For each codec, there is a maximum possible Network MOS that represents the best possible Listening Quality MOS under perfect network conditions. The following table shows the codec typically used in a scenario and the corresponding maximum Network MOS.

Table 1. Codecs Used in Scenarios with Maximum Network MOS

* The codec used in PC-PSTN can either be Siren or RTAudio NB depending on the configuration of the Mediation Server.

Because the maximum Network MOS varies depending on the scenario (because different codecs are used), it is usually more interesting to look at the average degradation of the Network MOS during the call. The average degradation can be broken down into how much is due to network jitter and how much is due to packet loss. For very small degradations, the cause of the degradation may not be available.

Conversational MOS

Conversational MOS is a prediction of the narrowband Conversational Quality (MOS-CQ) of the audio stream that is played to the user. This value takes into consideration the listening quality of the audio played and sent across the network, the speech and noise levels for both audio streams, and echoes. It represents how a large group of people would rate the quality of the connection for holding a conversation.

The Conversational MOS varies depending the same factors as Listening MOS, as well as the following:

• Echo

• Network delay

• Delay due to jitter buffering

• Delay due to devices

Due to the large number of factors that influence this value, it is most useful to view the Conversational MOS statistically rather than by using a single value.

LAN Congestion

As a LAN becomes more congested with traffic, the rates of packet loss and amount of jitter will increase for calls that pass through the LAN. This increase in packet loss and jitter will be reflected in lower Network MOSs and higher average degradation for these calls. Using the QoE Trend reports, the lower Network MOSs can be seen for the past several weeks and can be used to identify the LAN that is exhibiting signs of congestion. The call list report for calls on that LAN will show higher degradation, jitter and packet loss when compared to calls made before the LAN was congested or when compared to calls made on similar un-congested networks.

Bad Devices or Device Drivers

The audio quality for a call is affected by the microphone device and associated driver used to capture the audio from the person speaking. If a new device is used or a new driver for the device is deployed that results in lower audio quality capture, this is reflected in lower Sending MOS. Using the device report, the Sending MOS for these devices can be compared to other devices and against historical data to isolate a problematic device or device driver which can then be addressed. It is important to note that to identify problematic devices or drivers, they must be deployed and used enough to generate sufficient data for analysis. A single rarely used problematic device will not be identifiable using this report.