800 Mbps in Under an Hour: Fixing a Throttled Mesh Network
A client on a TP-Link Deco mesh system was stuck at ~40/20 Mbps despite paying for high-speed internet. We uncovered a QoS throttle and a faulty Ethernet link, then restored full performance in under an hour.
Key Results
From ~40/20 Mbps to ~800/200 Mbps over WiFi with stable coverage and consistent throughput across the property.
The Problem
Performance was poor everywhere in the property despite a premium internet package and a modern mesh setup.
Symptoms
The network felt slow across all rooms, with no outages or ISP faults.
- ~40 Mbps download
- ~20 Mbps upload
- Poor WiFi everywhere
What the client tried
Common fixes did not improve performance.
- Reboots and resets
- Settings changes in the Deco app
- Testing multiple devices
The Diagnostic
We ran a layered diagnostic: configuration first, then physical infrastructure. Two issues were stacking.
Issue 1: QoS Misconfiguration
QoS limits were set far below the actual internet speed, throttling the network.
- QoS disabled
- Immediate jump to ~100/100 Mbps
Issue 2: Faulty Ethernet Cable
The Ethernet link between the Deco router and fiber modem failed under load.
- Cable tested professionally
- Cable replaced
- Router rebooted
Result: Full Speed Restored
The mesh performed as expected once the throttling and bottleneck were removed.
- ~800 Mbps download over WiFi
- ~200 Mbps upload
- Stable coverage
Results in Under an Hour
A fast, repeatable process that isolated both issues without guesswork.
Disable QoS
Removed an artificial bandwidth cap applied by the mesh system.
Test the uplink
Used a cable tester to verify the Ethernet link to the fiber modem.
Replace and reboot
Replaced the faulty cable and rebooted to force a clean link negotiation.
Verify performance
Confirmed ~800/200 Mbps over WiFi with consistent coverage.
Key Takeaways
Misconfigured QoS can massively restrict performance
Even on gigabit connections, a low QoS cap will throttle the network across every device.
Partial improvements often signal a physical bottleneck
If speeds improve but remain far below expectation, cabling or hardware may still be limiting throughput.
Cable faults are invisible to software diagnostics
A cable tester and a clean link renegotiation are essential to confirm a healthy uplink.
Need help with slow WiFi?
Book a consult or start diagnostics and we will pinpoint the bottleneck.