What is packet loss? How to spot it and fix it

What happens to lost packets?

Web pages, file downloads and speed tests notice a missing packet and ask for it again. The data eventually arrives complete, but every resend costs time and the connection slows for a while. So in these jobs loss shows up as slowness, not as an error.

Video calls, voice chat and games can't afford to wait: audio that arrives late is useless. These apps skip the missing packet. That's where loss is felt directly: words drop out, video pixelates, moves are skipped in games.

Does packet loss show in a speed test?

The browser test can't measure packet loss; the HIZTESTI apps also show loss during a test. The browser test runs over connections that resend lost packets, so there loss shows up not as its own line but as low or unsteady speed and high jitter.

In our measurements typical jitter is 10.3 ms on mobile networks and 3.3 ms on fixed lines; packet loss can be one of the reasons jitter is higher on mobile. If your speed keeps rising and falling during a test and jitter is high, packet loss may be behind it.

How can you check for packet loss?

1. Open Command Prompt (Windows) or Terminal (Mac) on your computer.
2. First ping your router: on Windows "ping -n 100 192.168.1.1", on a Mac "ping -c 100 192.168.1.1" (if your router's address is different, it's on the label underneath). It takes about 100 seconds and only measures inside your home.
3. Then do the same to an internet address, for example "hiztesti.com". That address isn't our server but the nearest Cloudflare location; it still measures the path from your home to the internet.
4. The summary line at the end of each run says how many packets were lost.
5. If the router shows loss, the problem is inside your home (usually Wi-Fi); if the router is clean but the outside address isn't, the problem may be further along the line.

On a healthy wired line loss should be very close to zero. Some internet servers give ping replies low priority, so occasional loss seen only on an outside address can be misleading. If you see regular loss even over a cable, and it repeats at different times, record the results and pass them to your provider.

The most common causes

• Weak or crowded Wi-Fi: neighbouring networks and walls corrupt packets. The Wi-Fi guide shows how to tell.
• Mobile signal: loss rises when the signal is weak or the cell tower is busy; see mobile signal.
• An overloaded line: when the router's queue overflows, new packets get dropped. It has the same root as bufferbloat.
• A faulty or old cable, a loose connector, an overheating router.

Reducing packet loss

1. Use a wired connection for anything important.
2. Restart the router; queue problems can build up on routers left on for a long time.
3. Try replacing the cable into the router and the one to your computer.
4. Turn on QoS or SQM on your router if it has it; it reduces dropped packets when the line is busy.
5. If there's constant loss on a wired connection, call your provider; only they can fix loss on the line itself.

Run a test first to see where your result sits. Start a speed test