Case Studies / Featured Case
900 to 100 Mbps for No Reason — Tracing It to Faulty In-Wall Cabling
1000M plan · FTTPIntermittent speed dropRemote video diagnosisRoot cause: in-wall port
A 1000 Mbps plan on a WiFi 7 router, freshly set up. In the morning, speed tests hit 900+ Mbps. By the afternoon — nothing touched, nothing moved — the same phone in the same spot tested under 100 Mbps. The ISP swore their side was fine. This is the kind of "it's haunted" fault that wastes days if you're guessing.
Ruling things out, one layer at a time
A random-looking speed drop can come from a dozen places, so we ruled them out in order over a video call. The WiFi 7 router — brought over from overseas — was working fine and its admin settings were correct. The ISP had confirmed the line itself was healthy. If it's not the router and not the line, the problem lives in between: the physical wiring. Luckily the customer had a laptop that could plug straight into the wall port with a cable, which let us test the wired path directly instead of guessing over WiFi.
The culprit: an in-wall port that couldn't hold Gigabit
- The in-wall Ethernet run feeding the router was damaged or poor quality, so the port kept negotiating an unstable link rate — sometimes a full 1000 Mbps, sometimes dropping to 100 Mbps.
- That single flapping port perfectly explained the "900 in the morning, under 100 by afternoon" pattern — every time it renegotiated down to Fast Ethernet, the whole connection was capped.
- The room only had two wall ports to begin with: one was completely dead, and the one in use couldn't hold gigabit. Classic botched-installer cabling.
With the root cause pinned down, we handed over a clear fix plan matched to the customer's budget — which port to re-run or replace, and how to get a stable gigabit path to the router.
How to spot this one yourself
If your speed randomly swings between full-plan and about 100 Mbps, and both the ISP and the router check out, suspect the physical layer. On a wired connection, look at the port's link speed (e.g. in Windows adapter status): a healthy gigabit run reports 1.0 Gbps, while a bad cable or port often falls back to 100 Mbps. A connection that keeps flip-flopping between the two is the tell-tale sign of a marginal cable or wall port — not your internet plan.
Result
A "haunted" speed drop pinned to a single faulty in-wall port — diagnosed remotely, with a budget-matched fix plan so the 1000M plan could finally run at 1000M.