Bytes Sent
Total bytes of RTP payload transmitted by the endpoint — verify bandwidth usage matches codec expectations and SLA limits.
Bytes Sent
| Property | Value |
|---|---|
| Key | bytes_sent |
| Unit | Bytes |
| Type | Counter |
| Direction | Send |
| RFC | RFC 3550 |
What It Measures
Bytes Sent counts the total number of bytes of RTP payload data transmitted by the endpoint since the start of the media stream. This measures the actual media data placed on the wire, giving you a concrete picture of bandwidth consumption.
For audio, a G.711 codec at 64 kbps with 20ms packets produces 160 bytes per packet. Over 60 seconds, that is approximately 480,000 bytes (480 KB) of payload. Video codecs produce significantly more data, varying with resolution, frame rate, and scene complexity.
Why It Matters
- Bandwidth verification — Confirm that actual bandwidth usage matches what the codec and configuration should produce. Unexpected values indicate misconfiguration or codec behavior issues.
- SLA compliance — Many network contracts specify bandwidth limits. Bytes sent lets you verify that your VoIP traffic stays within allocated capacity.
- Capacity planning — Multiply per-endpoint byte rates by your target concurrent call count to estimate total bandwidth requirements.
- Anomaly detection — A sudden change in bytes sent without a corresponding configuration change may indicate codec switching, comfort noise insertion, or stream corruption.
How CallMeter Measures It
CallMeter tracks the cumulative RTP payload bytes transmitted by the endpoint. This counter is updated per second and also reported in RTCP Sender Reports as defined in RFC 3550.
Thresholds
This metric does not have fixed thresholds. Expected values depend on codec and media type:
| Configuration | Expected Rate | 60s Total |
|---|---|---|
| G.711 audio (20ms ptime) | ~8 KB/s | ~480 KB |
| Opus audio (20ms ptime) | ~4-8 KB/s | ~240-480 KB |
| H.264 video (500 kbps) | ~62 KB/s | ~3.7 MB |
| VP8 video (1 Mbps) | ~125 KB/s | ~7.5 MB |
What Causes Unexpected Values
- Lower than expected — Silence suppression or comfort noise reducing payload during quiet periods. Voice Activity Detection (VAD) reduces transmission when no speech is detected.
- Higher than expected — Redundancy encoding (RFC 2198), FEC, or larger-than-configured payload sizes.
- Stops incrementing — Endpoint stopped transmitting. Same causes as Packets Sent counter plateau.
How to Fix It
- Calculate average packet size. Divide bytes sent by Packets Sent. The result should match your codec's expected payload size.
- Compare with bitrate. The Send Bitrate metric shows the same data as a per-second rate, which is easier to compare against bandwidth limits.
- Check codec configuration. If bytes per packet do not match expectations, verify the codec and packetization interval in your test configuration.
Related Metrics
- Bytes Received — Reception counterpart; compare for asymmetric bandwidth usage
- Send Bitrate — Bytes sent expressed as a per-second bitrate
- Packets Sent — Divide bytes by packets for average packet size