Call Quality Metrics

The following metrics are available from UC Monitor reports.

ACOM

(Cisco PSTN calls only) The total echo return loss on the network. ACOM measures how significantly the voice gateway reduced the echo. ACOM includes echo reduction that occurs with or without the activity of an echo cancellation device.

Burst

(Microsoft only) The points in a data stream when a high percentage of packets is lost or discarded due to packets arriving late.

Burst Density. The percentage of packets within burst periods that are lost or discarded.
Burst Duration. The average duration of all high-loss periods in a data stream.

Concealment Ratio

(Cisco only) A technique for masking the effects of packet loss in VoIP communications. Also known as packet loss concealment (PLC).

Cumulative Concealment Ratio. The percentage of all call seconds that had concealment events due to lost data.
Maximum Concealment Ratio. The highest concealment ratio value during the call.
Severely Concealed Seconds. The number of call seconds that had more than 5 percent concealment events from the start of the audio stream.

Echo Tail Length

(Avaya only) The “length” of echo cancellation processing. Based on the distance between a voice gateway and the endpoint. Typical values range from 8 milliseconds to 32 milliseconds.

Event Counts

(Microsoft only)

Device Howling. The number of times during a call that two or more devices in the same room or acoustic environment caused howling or screeching in the audio.
Device Multiple Endpoints. The number of times during a call that multiple devices were detected in the same room or acoustic environment.

Event Ratios

(Microsoft only)

CPU Insufficient. The fraction of a call during which CPU resources were insufficient and caused poor audio quality.
Device Capture Not Functioning. The fraction of a call during which the capture device did not function properly. A capture device, such as a microphone or webcam, transmits audio.
Device Clipping. The fraction of a call during which clipping in the captured data caused poor quality of the sent audio. Clipping is a distortion in an audio signal caused when the tops of high-amplitude peaks are cut off.
Device Echo. The fraction of a call during which echo caused poor quality of the sent audio.
Device Glitches. The fraction of a call during which gaps (glitches) caused poor audio quality.
Device Half Duplex AEC. The fraction of a call during which the acoustic echo canceller (AEC) operated in half-duplex mode. This mode adversely affected real-time, two-way communication.
Device Low SNR. The fraction of a call during which low speech-to-noise levels caused poor quality of the sent audio.
Device Low Speech Level. The fraction of a call during which low speech levels caused poor quality of the sent audio.
Device Near End to Echo Ratio. The fraction of a call during which the ratio of near-end-signal-level to echo-level caused poor audio quality.
Device Render Mute. The fraction of a call during which the render device is muted. A render device, such as a headset or speakers, receives audio.
Device Render Not Functioning. The fraction of a call during which the render device did not function properly. A render device, such as a headset or speakers, receives audio.
Device Render Zero Volume. The fraction of a call during which the volume of the render device is set to 0 (zero). A render device, such as a headset or speakers, receives audio.
Network Bandwidth Low. The fraction of the call during which the amount of available bandwidth (or bandwidth policy) was low enough to cause poor quality of the sent audio.
Network Delay. The fraction of a call during which the network delay was significant enough to adversely affect real-time, two-way communication.
Network Receive Quality. The fraction of a call during which the network caused poor quality of the received audio.
Network Send Quality. The fraction of a call during which the network caused poor quality of the sent audio.

Gap

(Microsoft only)

Gap Density. The percentage of lost or discarded packets in the gaps between bursts in a data stream.
Gap Duration. The average duration of periods of good performance (low loss) between periods of data loss in a data stream. Occasionally, gap duration exceeds the call duration.

Jitter

Packet delay that distorts the quality of a voice conversation. In charts, maximum jitter values are graphed as data points and indicated on the right Y-axis.

The definition of Maximum Jitter varies by monitored environment:

Avaya environment: The maximum jitter per interval
Cisco environment: The maximum jitter thus far

Jitter Buffer

Jitter Buffer Delay. (Avaya only) Delay that the jitter buffer introduces while it holds one or more packets to reduce variations in packet arrival times. Acceptable jitter buffer delay is two RTP datagrams or less. Because most codecs have a datagram size of 20 to 30 milliseconds, a good jitter buffer delay is no more than 40 to 60 milliseconds.
Jitter Buffer Loss. (Cisco only) The packets that are lost when jitter hinders the caching capacity of the jitter buffer.
Jitter Buffer Over Runs. (Avaya only) The number of times that jitter exceeded the maximum size setting of the jitter buffer. Packets arrive too quickly to be contained by the jitter buffer. Over runs usually result in packet loss.
Jitter Buffer Under Runs. (Avaya only) The number of times that the jitter buffer became empty. Packets arrive too slowly to be contained by the jitter buffer. Under runs usually indicate that delays are too lengthy for the buffer setting.

Note: Avaya endpoints have a limitation that affects the way the Over Runs and Under Runs metrics are reported. The maximum value is 255. In a report, this cumulative value means that the value was greater than 255, and the actual maximum value cannot be reported. These values, reported every 15 seconds during a Call Watch, are additive. After the maximum is reached, Jitter Buffer Over Runs and Under Runs charts show 0 values for successive intervals until the call is completed.

Latency

One-way delay. Calculated from the origination party to the destination party. Includes propagation delay, network delay, and packetization delay. Latency has a severe effect on VoIP call quality.

Mean Opinion Score (MOS)

The Mean Opinion Score (MOS) is an industry standard method for gauging call quality. MOS is an estimation of how impairments to a voice signal affect listener perception of call quality.

MOS is the average MOS listening quality (LQK) score observed for the bi-directional voice stream.
MOS (Min) is the lowest LQK score observed.
(Microsoft only) Conversational MOS is based on MOS values from both directions of data flow.
Listening MOS is based on call legs traveling toward the endpoint to reflect listener perception of quality.

Network MOS

MOS listening quality that is based only on network factors, such as codec, packet loss, packet reordering, packet errors, and jitter.

Noise Level

(Microsoft only) The average portion of an audio signal that is noise and not actual voice data. Measured in decibels.

Packet Loss

The percentage of data packets that were lost in transit. These packets were sent but never received at the destination.

Packet Loss. The average loss rate.
Packet Loss (Max). (Avaya only) The maximum loss rate.
Packets Received. A means of gauging the size of the data stream.
Packets Lost. The difference between the number of packets that were sent and the number of packets that were received.

Sequence

(Avaya only)

Sequence Jumps. The number of times that at least one consecutive packet was lost.
Sequence Falls. The number of times that at least one packet arrived out of order.

Signal Level

(Cisco PSTN calls only) The average audio signal level in decibels. The dBm0 abbreviation refers to decibels relative to a power level of one milliwatt (dBm) measured at a zero transmission level.

Signal in. The signal level of the data traveling into the echo canceler.
Signal out. The signal level of the data traveling out of the echo canceler toward the IP network.

Time-To-Live

A counter embedded in data to prevent a data packet from circulating through the network indefinitely. The counter decrements each time that the packet passes through a router or a switch. The minimum and maximum TTL values are provided.