Configuring Voice Quality for Registered Users

You can configure the device to measure the mean opinion score (MOS) of calls belonging to users that are registered with the device.

During the call, the device measures MOS every 30 seconds. The device provides MOS measurements as values (MOS * 10, i.e., 0 to 50), and colors (green, yellow, or red) according to your Quality of Experience Color rules (see Configuring Quality of Experience Profiles). Whenever a change in MOS color occurs, the device reports this to the registered user, by sending an out-of-dialog SIP NOTIFY message containing the proprietary SIP header 'x-VoiceQuality: <Value> <Color>', as shown in the following example (MOS 3.2 and red color):

x-VoiceQuality: 32 red

You can configure the device (see Configuring Quality of Service Rules) to take one of the following actions if it detects a low MOS level during a call:

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Reject new calls (destined to the IP Group) for a user-defined time.

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Change the IP Profile during the call. Using an alternative IP Profile is especially useful if you want to use a different voice coder that is more efficient (e.g., Opus) than the coder (e.g., G.711) currently used for the call. In this scenario, if the device measures low MOS, it immediately uses the alternative IP Profile, switching to the more efficient coder (e.g., Opus). If at any stage during the call, the device detects an improvement in the network (based on packet loss), it uses the original IP Profile, switching back to the original coder associated with this IP Profile (e.g., G.711).

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This feature is applicable only to the SBC application.

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When implementing the alternative IP Profile method for Quality of Service:

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New calls will initially use the coder that was last used in the previous call (regardless of MOS).

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This feature is not supported for HA switchover (e.g., if coder changed to Opus before switchover, after switchover the call remains with Opus until it ends, regardless of MOS level).

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If the device supports other media types (e.g., video) in addition to audio, at least one of the peers must support re-INVITE without SDP.

In addition to real-time MOS measurements discussed above, the device performs average MOS calculations per registered user. The device measures MOS in an "observation window" that is comprised of 12 intervals, where each interval can be configured as one hour (i.e., total of 12 hours in the window) or two hours (total of 24 hours in the window). Based on these intervals, the device provides the following MOS measurements:

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Average MOS of the 12 intervals (i.e., average MOS is calculated per interval - this is the average of these 12 MOS average measurements)

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Minimum average MOS of the 12 intervals (i.e., lowest MOS average measured for an interval)

The average MOS of each interval is calculated by "weight" of call duration relative to total call duration in the interval. For example, If the observation interval is 1 hour and two calls occurred in an interval, one that lasted 10 minutes with MOS of 4.2 and another call that lasted 20 minutes with MOS of 3.7, the average MOS is calculated as follows: 4.2 * 10 / 30 + 3.7 * 20 / 30 = 3.86

You can view MOS measurements per registered user in the SBC Registered Users table (see Viewing SBC Registered Users).

The device calculates MOS based on RTCP-XR reports received form the user. However, for WebRTC users, which typically don't send RTCP-XR reports, the device calculates MOS based on RTCP packets. For more information on WebRTC, see WebRTC.

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To configure MOS measurement of registered users:

Open the Registered User Voice Quality page (Setup menu > Signaling & Media tab > Media folder > Quality of Experience > Registered User Voice Quality); the following appears:

Configure the following:

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In the 'Registered User MOS Observation Window' field, enter the duration (in hours) of each of the 12 intervals for measuring MOS.

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In the 'MOS Stored Timeout For No Calls' field, enter the time (in minutes) of no calls for a registered user after which the MOS measurement for that user is deleted (reset to zero).

Configure a QoE Profile to define the severity-color thresholds for MOS (see Configuring Quality of Experience Profiles).

(Optional) Configure a Quality of Service rule to define what action to take (reject future calls or use an alternative IP Profile) when a specific MOS severity level occurs (see Configuring Quality of Service Rules). Make sure that you configure the 'Rule Metric' parameter to Registered User Voice Quality.

(See note below) In the IP Group of the registered user, configure the 'User Voice Quality Report' parameter to Enable:

If you configure a Quality of Service rule (in Step 4), it's unnecessary to enable the MOS calculation and reporting feature in the IP Groups table (Step 5). If you don't configure a Quality of Service rule, then you need to enable the feature in the IP Groups table.