Metrics Reference
Complete reference for CallMeter's 150+ real-time VoIP quality metrics. Understand every measurement across quality, network, feedback, jitter buffer, audio, video, and call timing categories.
Metrics Reference
CallMeter collects over 150 real-time measurements per endpoint per second during every test and probe execution. These metrics give you complete visibility into what is happening on the wire, from high-level quality scores like MOS down to individual packet timing measurements.
This reference documents every metric: what it measures, why it matters, and how to interpret it.
Metric Categories
CallMeter organizes metrics into seven categories, each covering a different layer of the VoIP stack.
Quality
The headline metrics that summarize call quality into actionable numbers. Start here when evaluating test results.
| Metric | Key | Unit | What It Tells You |
|---|---|---|---|
| MOS Score | mos | 1-5 | Overall voice quality rating |
| R-Factor | r_factor | 0-100 | Transmission quality rating |
| Jitter | jitter_ms | ms | Packet arrival time variation |
| Round Trip Time | rtt_ms | ms | Network latency |
| Packets Lost | packets_lost | packets | Absolute packet loss count |
| Packet Loss Rate | fraction_lost | % | Percentage of packets lost |
| Clock Drift | clock_drift_estimate | ppm | Hardware clock accuracy |
| Clock Skew | clock_skew_estimate | ppm | Sender-receiver clock difference |
| Timestamp Jumps | timestamp_jumps | jumps | RTP timestamp discontinuities |
Network
Transport-level measurements that show what is happening at the packet level. Use these to diagnose the root cause when quality metrics show degradation.
| Metric | Key | Unit | What It Tells You |
|---|---|---|---|
| Packets Sent | packets_sent | packets | Total packets transmitted |
| Packets Received | packets_received | packets | Total packets received |
| Bytes Sent | bytes_sent | bytes | Total data transmitted |
| Bytes Received | bytes_received | bytes | Total data received |
| Packets Sent Rate | packets_sent_rate_ps | pps | Transmission rate |
| Packets Received Rate | packets_recv_rate_ps | pps | Reception rate |
| Send Bitrate | bytes_sent_rate_bps | bps | Outbound bandwidth |
| Receive Bitrate | bytes_recv_rate_bps | bps | Inbound bandwidth |
| Duplicate Packets | duplicate_packets | packets | Packets received more than once |
| Out-of-Order Packets | out_of_order_packets | packets | Packets arriving in wrong order |
| Sequence Resets | sequence_number_resets | resets | Sequence counter restarts |
| Sequence Gaps | sequence_number_gaps | packets | Burst loss event sizes |
| Sequence Jumps | sequence_number_jumps | jumps | Large sequence discontinuities |
| Max Packet Spacing | max_packet_spacing | ms | Largest gap between packets |
| Min Packet Spacing | min_packet_spacing | ms | Smallest gap between packets |
| Avg Packet Spacing | avg_packet_spacing | ms | Average gap between packets |
Feedback
RTCP feedback messages exchanged between endpoints. Includes NACK counts, PLI requests, FIR messages, and REMB bandwidth estimates. These metrics are critical for understanding how endpoints react to quality problems. (Detailed pages coming soon.)
Jitter Buffer
Receiver-side buffering metrics including buffer size, delay, target level, and overflow/underflow events. These reveal how well the receiver is coping with network jitter. (Detailed pages coming soon.)
Audio
Codec-specific audio measurements including audio levels, silence detection, comfort noise, and DTMF event tracking (digits sent and received via RFC 4733 RTP or SIP INFO). (Detailed pages coming soon.)
Video
Encoding and playback metrics including frame rate, resolution changes, keyframe intervals, freeze events, and picture quality indicators. (Detailed pages coming soon.)
Call Timing
SIP signaling timing measurements captured once per call: post-dial delay, time to ringing, setup time, and call duration. Unlike the categories above, these are one-shot values rather than time-series data. (Detailed pages coming soon.)
Time-Series vs One-Shot Metrics
Most CallMeter metrics are time-series measurements. The platform samples them every second throughout the call and records each data point with a timestamp. This produces a continuous timeline that you can chart, zoom into, and correlate across endpoints.
One-shot metrics are captured once per call and represent a single event or duration. Call timing metrics like post-dial delay and setup time fall into this category. They appear as single values in the results summary rather than as charts.
Send vs Receive Direction
Every metric has a direction: send or receive.
- Send metrics describe what the endpoint is transmitting. For example,
packets_sentcounts outbound RTP packets, andbytes_sent_rate_bpsmeasures outbound bitrate. - Receive metrics describe what the endpoint is receiving from the remote side. For example,
jitter_mson the receive side measures how much the incoming packet arrival times vary.
Some metrics are meaningful in both directions. Packet counts, byte counts, and bitrates exist for both send and receive. Quality scores like MOS and R-Factor are computed per direction based on the conditions observed in that direction.
Filtering by Direction
In the CallMeter dashboard, use the direction filter on any endpoint detail view to isolate send or receive metrics. This is essential when diagnosing asymmetric quality issues where one direction is degraded but the other is fine.
Using This Reference
Each metric page in this reference follows a consistent structure:
- What it measures — Plain-language explanation followed by technical detail
- Why it matters — Business and operational impact
- How CallMeter measures it — Measurement methodology
- Thresholds — Good, warning, and critical ranges (where applicable)
- Common causes of problems — What drives this metric out of range
- How to fix it — Actionable remediation steps
- Related metrics — Cross-references to metrics that provide additional context
Start with the Quality metrics for the high-level picture, then drill into Network metrics when you need to understand the underlying transport behavior.