# How to Test Fibre Speed Correctly (Wired vs WiFi)

Source: https://urbanx.co.za/knowledge-hub/fno-troubleshooting/test-fibre-speed-correctly

**Answer:** 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.

Part of [FNO Troubleshooting & Fibre Diagnostics](https://urbanx.co.za/knowledge-hub/fno-troubleshooting) · 6 min read · by UrbanX Network Operations

## 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

> **WARNING:** 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 |

> **INFO:** Only wired testing isolates access-layer performance.

## Step-by-Step Fibre Speed Test Procedure

1. **Connect via Ethernet**
   - Plug laptop or PC directly into router LAN port.
2. **Disable WiFi on Device**
   - Ensure traffic flows only through Ethernet.
3. **Close Background Applications**
   - Pause:
   - Cloud sync.
   - Game downloads.
   - Updates.
   - Streaming.
4. **Restart Router (Optional)**
   - Only if stable PON and no LOS.
5. **Run 3 Speed Tests**
   - Space them 2–3 minutes apart.
6. **Test at Different Times**
   - Off-peak (morning/afternoon).
   - Peak (evening).
7. **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

- **Line Speed** — The maximum bandwidth provisioned at the access layer.
- **Throughput** — The actual measured data transfer rate.

> **INFO:** 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, this is not your fault domain:
- LOS is red
- PON flashes continuously

Then the issue is signal-related, not speed testing error.

## Frequently Asked Questions

**Why is my WiFi slower than my fibre plan?**

WiFi introduces interference, distance loss, and device limitations.

**Is 2.4GHz slower than 5GHz?**

Yes. 2.4GHz prioritizes range over speed.

**Should I test on my phone?**

No. Phones often limit throughput and rely on WiFi.

**Does Ethernet guarantee full speed?**

It provides the most accurate measurement of access-layer speed.

**How much speed variation is normal?**

A 5–10% difference from plan speed is normal due to overhead.