To test fibre speed accurately, connect a device via Ethernet directly to your router, disable background traffic, and run multiple tests. WiFi testing — especially on 2.4GHz or mesh — does not reflect true line speed and should not be used for fault escalation.
What the Problem Means
Many "slow fibre" reports are caused by incorrect testing methods.
If your:
- PON is solid green
- LOS is off
- Connection works but feels slow
You must first determine whether the issue is:
- Access-layer throughput
- Router limitation
- WiFi interference
- Device limitation
Testing correctly prevents unnecessary FNO escalation.
Why WiFi Tests Are Misleading
WiFi introduces variables unrelated to fibre line performance:
- Distance from router
- Wall interference
- 2.4GHz congestion
- Mesh backhaul limitations
- Neighbouring network overlap
WiFi speed ≠ fibre speed. Fibre speed must be tested over wired Ethernet.
Wired vs WiFi Accuracy Table
| Test Method | Reflects True Fibre Speed? | Reliability |
|---|---|---|
| Ethernet to router | Yes | High |
| 5GHz WiFi (near router) | Partial | Moderate |
| 2.4GHz WiFi | No | Low |
| Mesh satellite (wireless backhaul) | No | Low–Moderate |
| Powerline adapter | Variable | Moderate |
Only wired testing isolates access-layer performance.
Step-by-Step Fibre Speed Test Procedure
Connect via Ethernet
- Plug laptop or PC directly into router LAN port.
Disable WiFi on Device
- Ensure traffic flows only through Ethernet.
Close Background Applications
- Pause:
- Cloud sync.
- Game downloads.
- Updates.
- Streaming.
Restart Router (Optional)
- Only if stable PON and no LOS.
Run 3 Speed Tests
- Space them 2–3 minutes apart.
Test at Different Times
- Off-peak (morning/afternoon).
- Peak (evening).
Compare Against Plan Speed
- Small variance (5–10%) is normal.
If wired speeds match your plan, fibre is working correctly.
Definition: Throughput vs Line Speed
The maximum bandwidth provisioned at the access layer.
The actual measured data transfer rate.
WiFi interference reduces throughput but does not indicate fibre signal failure.
South African Context
In dense suburbs:
- 2.4GHz WiFi channels are heavily congested
- Evening demand increases interference
- Apartment blocks amplify wireless overlap
Users often misinterpret WiFi slowdown as fibre underperformance.
When to Escalate
Escalate only when:
- Wired Ethernet speed is significantly below plan
- Results persist outside peak hours
- Multiple devices confirm same issue
- ONT shows stable signal (PON solid, LOS off)
Do not escalate based on WiFi-only results.
Typical performance investigation windows:
- 24–48 hours for line testing
- Longer if access-layer congestion analysis required
When This Is NOT the Issue
If all of the following are true:
- LOS is red
- PON flashes continuously
Then the issue is signal-related, not speed testing error.
See our ONT light status guides