Metrics Glossary
Quick reference table of all 90+ CallMeter VoIP metrics organized by category, with keys, units, and links to detailed documentation.
This glossary lists every metric CallMeter collects during test and probe execution. Each metric links to its detailed documentation page with thresholds, measurement methodology, and troubleshooting guidance.
For an introduction to how metrics work, see the Metrics Reference overview.
Quality
Core VoIP quality scores that summarize call experience into actionable numbers.
| Metric | Key | Unit | Description |
|---|---|---|---|
| MOS Score | mos | 1-5 | Mean Opinion Score — overall voice quality rating (E-model, G.107) |
| R-Factor | r_factor | 0-100 | Transmission quality rating (G.107) |
| Jitter | jitter_ms | ms | Inter-arrival time variation |
| Round Trip Time | rtt_ms | ms | Network round-trip latency |
| Packets Lost | packets_lost | packets | Cumulative lost packet count |
| Packet Loss Rate | fraction_lost | % | Percentage of packets lost per interval |
| Clock Drift | clock_drift_estimate | ppm | Hardware clock frequency accuracy |
| Clock Skew | clock_skew_estimate | ppm | Sender-receiver clock offset |
| Timestamp Jumps | timestamp_jumps | count | RTP timestamp discontinuities |
Network
Transport-layer packet and bandwidth measurements.
| Metric | Key | Unit | Description |
|---|---|---|---|
| Packets Sent | packets_sent | packets | Total RTP packets transmitted |
| Packets Received | packets_received | packets | Total RTP packets received |
| Bytes Sent | bytes_sent | bytes | Total payload bytes transmitted |
| Bytes Received | bytes_received | bytes | Total payload bytes received |
| Send Rate | packets_sent_rate_ps | pps | Outbound packet rate |
| Receive Rate | packets_recv_rate_ps | pps | Inbound packet 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 | out_of_order_packets | packets | Packets arriving out of sequence |
| Sequence Resets | sequence_number_resets | count | Sequence number counter restarts |
| Sequence Gaps | sequence_number_gaps | packets | Burst loss event sizes |
| Sequence Jumps | sequence_number_jumps | count | Large sequence discontinuities |
| Max Spacing | max_packet_spacing | ms | Largest inter-packet gap |
| Avg Spacing | avg_packet_spacing | ms | Average inter-packet gap |
| Expected Packets | expected_packets | pkts | Packets expected per sequence-number reasoning |
| Late Packets | late_packets | pkts | Packets arriving after jitter-buffer deadline |
| SSRC Switches | ssrc_switches | events | RTP SSRC changes within a session |
| SRTP Decrypt Failures | srtp_decrypt_failures | events | SRTP decryption failure count |
| Local ICE Candidate | local_candidate_type | — | ICE candidate type used locally (host/srflx/prflx/relay) |
| Remote ICE Candidate | remote_candidate_type | — | ICE candidate type used remotely (host/srflx/prflx/relay) |
Feedback
RTCP feedback messages exchanged between endpoints for error recovery and quality adaptation.
| Metric | Key | Unit | Description |
|---|---|---|---|
| NACK | nack_count | count | Negative acknowledgement requests (packet retransmission) |
| PLI | pli_count | count | Picture Loss Indication requests (video keyframe) |
| FIR | fir_count | count | Full Intra Request (force keyframe) |
| SLI | sli_count | count | Slice Loss Indication |
| SIP INFO PFU | sip_info_pfu | requests | SIP INFO Picture Fast Update requests (RFC 5168) - non-RTCP keyframe request signaling |
| RTCP SR/RR Cadence | rtcp_sr_rr_interval_ms | ms | Interval between RTCP SR/RR messages |
Jitter Buffer
Receiver-side adaptive buffer metrics showing how well the endpoint handles network jitter.
| Metric | Key | Unit | Description |
|---|---|---|---|
| Current Delay | jitter_buffer_delay | ms | Current jitter buffer delay (ms) - gauge metric from GStreamer rtpjitterbuffer |
| Target Delay | jitter_buffer_target | ms | Target jitter buffer delay (ms) - configuration reference from GStreamer |
| Late Packets | jitter_buffer_late | packets | Packets arriving after playout deadline |
| Average Jitter | jitter_buffer_avg_jitter | ms | Buffer-observed jitter estimate |
| Packet Losses | jitter_buffer_losses | packets | Packets declared lost by buffer |
| Duplicates | jitter_buffer_duplicates | packets | Duplicate packets detected by buffer |
| Packets Pushed | jitter_buffer_pushed | packets | Packets pushed out for playout |
| RTX Requests | jitter_buffer_rtx_requests | count | Retransmission requests sent |
| RTX Success | jitter_buffer_rtx_success | count | Successful retransmissions received |
Audio
Audio-specific quality measurements and codec diagnostics.
| Metric | Key | Unit | Description |
|---|---|---|---|
| PLC Events | plc_events | count | Packet Loss Concealment activations |
| PLC Duration | plc_duration | ms/s | Total PLC duration from Opus decoder - opusdec plc-duration property (cumulative, Opus codec only) |
| Signal Level | audio_signal_level_rms_dbov | dBov | Audio signal power |
| Noise Level | audio_noise_level_rms_dbov | dBov | Background noise power |
| Speech Activity | vad_speech_ratio | % | Voice Activity Detection ratio showing DTX/VAD behavior and bandwidth savings |
| Comfort Noise | comfort_noise_inserts | inserts/s | Comfort noise insertion rate providing concealment visibility |
| Opus Bandwidth | opus_bandwidth_khz | kHz | Opus decoder bandwidth in kHz (narrowband=4, mediumband=6, wideband=8, super-wideband=12, fullband=20) - indicates audio quality tier and frequency range of the encoded content |
| Opus Decoder Gain | opus_decoder_gain_db | dB | Opus decoder gain adjustment in dB - indicates output level normalization applied by decoder. Measured from opusdec in both send and receive paths. |
| Opus Packet Loss | opus_packet_loss_pct | % | Opus internal packet loss estimate |
| Opus Packet Duration | opus_last_packet_duration_ms | ms | Last Opus frame duration |
| Audio Level | audio_level_rms_dbov | dBov | Combined audio level measurement |
Video
Video encoding, playback, and quality measurements.
| Metric | Key | Unit | Description |
|---|---|---|---|
| Keyframe Requests Sent | keyframe_requests_sent | count | PLI/FIR requests transmitted |
| Keyframe Requests Received | keyframe_requests_received | count | PLI/FIR requests received |
| Keyframes Sent | keyframes_sent | count | I-frames transmitted |
| Keyframes Received | keyframes_received | count | I-frames received |
| Video Bitrate | video_bitrate_bps | bps | Video stream bandwidth |
| Video FPS | video_fps | fps | Frames per second |
| Resolution | resolution | MPx | Video resolution displayed as width×height (e.g., 640×480, 1920×1080) - shows adaptive bitrate changes |
| Keyframe Interval | keyframe_interval_ms | ms | Time between keyframes |
| Freeze Count | video_freeze_count | count | Video freeze events |
| Freeze Duration | video_freeze_duration_ms | ms | Total freeze time |
| Video Decoder Errors | video_decoder_errors | errors | Decoder recoveries from missing or corrupted reference data — whether decode failed outright or libav concealed the gap (a concealed loss often shows no freeze) |
Call Timing
One-shot SIP signaling measurements captured once per call.
| Metric | Key | Unit | Description |
|---|---|---|---|
| Time to Trying | time_to_trying_ms | ms | INVITE to 100 Trying |
| Time to Ringing | time_to_ringing_ms | ms | INVITE to 180 Ringing |
| Post-Dial Delay | pdd_ms | ms | Post-Dial Delay — time from INVITE to first ringback or media |
| Call Setup Time | call_setup_ms | ms | Total time from INVITE to 200 OK (call connected) |
| Time to First Media | time_to_first_media_ms | ms | INVITE to first RTP packet |
| Call Duration | call_duration_ms | ms | Total call length |
| Final Status Code | final_status_code | code | SIP response code ending the call |
| Call Result | call_result | enum | Overall call outcome classification |
Impairment
Counters emitted by CallMeter's built-in network impairment simulator. They report what the platform deliberately did to the stream, so a degraded result can be attributed to the injected condition rather than to the network under test.
| Metric | Key | Unit | Description |
|---|---|---|---|
| Impairment: Dropped | impairment_packets_dropped | packets | Packets dropped by impairment engine (random + burst loss) |
| Impairment: Delayed | impairment_packets_delayed | packets | Packets delayed by impairment engine (latency + jitter) |
| Impairment: Reordered | impairment_packets_reordered | packets | Packets reordered by impairment engine |
| Impairment: Duplicated | impairment_packets_duplicated | packets | Packets duplicated by impairment engine |
| Impairment: Throttled | impairment_packets_throttled | packets | Packets dropped by bandwidth limiter (token bucket) |
| Impairment: Avg Delay | impairment_avg_delay_ms | ms | Average delay added by impairment engine (ms) |
Related Pages
- Metrics Reference — Detailed introduction and usage guide
- Analyzing Results — How to interpret test run metrics
- Poor Quality Metrics — Troubleshoot quality degradation
Metrics Collection
How CallMeter collects 90+ real-time VoIP metrics per endpoint per second, organizes them by direction, and displays them in the dashboard.
SIP Response Codes
Comprehensive reference of SIP response codes from RFC 3261, organized by class with descriptions, common causes, and their meaning for VoIP testing in CallMeter.