The causes close to home
Most packet loss on home connections starts within a few metres of the router. Wifi is the biggest single cause. It is a shared radio channel where your devices, your neighbours' networks, Bluetooth, baby monitors and microwave ovens all compete for airtime. When a frame is corrupted, wifi retries it a few times and then gives up, and the packet is lost. The further you are from the router and the more walls in between, the more often that happens.
The second big cause is congestion on your own line. When a device uploads a large file, the router queues packets faster than the line can send them. Once the queue is full, new packets are dropped, including the small, urgent ones from a game or call. This is why a video call can fall apart the moment someone else in the house starts a cloud backup.
- Weak or crowded wifi. Loss that comes in bursts and gets worse with distance from the router.
- A full upload or download. Loss and ping spikes that line up with someone else's activity on the network.
- An overloaded or failing router. Loss that builds up over days and clears after a restart.
- A damaged cable or connector. Steady, even loss that does not change with time of day or activity.
The causes further away
- A line fault. Water in a junction box, a corroded connection or electrical noise on copper phone lines causes errors that the modem cannot correct. Often worse in wet weather.
- Provider congestion. An oversubscribed link at the exchange or in the provider's core, busiest between about 7 and 11pm.
- A bad route to one destination. A congested link between your provider and another network, which affects only some games or services.
- The far end. An overloaded game server or call bridge drops packets no matter how good your connection is.
Telling them apart with a test
The packet loss test draws each packet on a strip, so the pattern is visible directly: evenly spread red marks versus clusters. Run it in the conditions where the problem happens, then change one variable at a time.
| What the test shows | Most likely cause |
|---|---|
| Loss on wifi, none on a cable | Wifi signal or interference |
| Loss only while someone else downloads or uploads | Congestion on your own line |
| Loss everywhere, cleared by a router restart | Router overload or firmware |
| Steady loss on a cable, day and night | Cable, connector or line fault |
| Clean in the morning, loss in the evening | Provider congestion |
| Clean test, but loss in one game | The route to that game, or its servers |
Causes that get blamed but rarely are
DNS settings, the browser, antivirus software and "slow" plans are often blamed and seldom responsible. DNS only resolves names before a connection starts. A slower plan does not drop packets unless it is actually full. Antivirus and firewalls can block traffic entirely, which is a different failure from dropping a percentage of it; if a test cannot get any packets through at all, see UDP blocked.