Estimated Bandwidth — VoIP Congestion Detection Metric
Real-time bandwidth estimation using GCC/REMB algorithms. Detect congestion and capacity limits on the media path during SIP load testing.
Estimated Bandwidth
| Property | Value |
|---|---|
| Key | estimated_bandwidth_bps |
| Unit | Bits per second (bps) |
| Type | Gauge |
| Direction | Receive |
What It Measures
Estimated Bandwidth reports the receiver's estimate of available bandwidth on the media path, computed using Google Congestion Control (GCC) or Receiver Estimated Maximum Bitrate (REMB) algorithms. This value represents how much media data the network path can sustain without causing congestion.
Why It Matters
During SIP load testing and capacity planning, estimated bandwidth reveals the network's real capacity — not just what your link speed says, but what the path actually delivers under current conditions. When estimated bandwidth drops below the codec bitrate, quality degradation is imminent: the encoder cannot send at the rate needed for acceptable quality.
This metric is the earliest warning signal for congestion. It drops before packet loss appears, before jitter spikes, and before MOS degrades. Teams doing capacity planning watch this metric to find the exact point where their infrastructure saturates.
Thresholds
Thresholds depend on the codec and media type:
| Media Type | Minimum Bandwidth | Comfortable Bandwidth |
|---|---|---|
| G.711 audio | 64 kbps | 100+ kbps |
| Opus audio | 24 kbps | 48+ kbps |
| H.264 video (VGA) | 500 kbps | 1+ Mbps |
| H.264 video (HD) | 1.5 Mbps | 3+ Mbps |
If estimated bandwidth drops below the minimum for your codec, expect quality degradation.
What Causes Low Bandwidth Estimates
- Network congestion — Competing traffic saturates the link.
- QoS misconfiguration — Media traffic not prioritized, competing with bulk data.
- Shared links — Multiple endpoints sharing the same uplink.
- ISP throttling — Some ISPs throttle UDP traffic.
- Path change — BGP reconvergence routing through a lower-capacity path.
How to Fix It
- Correlate with endpoint count. If bandwidth drops as you add endpoints during a ramp test, you have found your capacity ceiling.
- Enable QoS marking. Use CallMeter's DSCP/QoS settings to mark media traffic with EF (Expedited Forwarding).
- Check the network path. Compare bandwidth estimates from cloud workers vs. on-premise workers to isolate where the bottleneck is.
Related Metrics
- Send Bitrate — What the sender is actually transmitting
- Receive Bitrate — What the receiver is actually receiving
- Packet Loss Rate — Loss that follows when bandwidth is insufficient
- Jitter — Jitter increases under congestion