Introduction You run Speedtest. It shows 200 Mbps download, 50 Mbps upload, 10ms ping. Everything looks great. Then you jump on a video call and it's choppy. Your game is rubber-banding. Your VoIP call sounds like the other person is underwater. What's going on?
The answer is packet loss — and Speedtest literally cannot see it.
Why TCP-Based Speed Tests Hide the Problem? Speedtest, Fast.com, and most popular speed tests use TCP (Transmission Control Protocol) to measure your connection.
TCP was designed to be reliable. When a packet gets lost, TCP automatically retransmits it. From the application's perspective, every packet eventually arrives — just slightly delayed. This is great for downloading files. It's terrible for measuring real network quality.
Here's what happens during a Speedtest on a bad connection:
Packet 1 → ✓ received Packet 2 → ✗ lost → retry → ✓ received Packet 3 → ✓ received
Packet 4 → ✗ lost → retry → retry → ✓ received Packet 5 → ✓ received
TCP result: 100% delivered. "Your connection is fine!"
TCP hides the retransmissions. Your speed test never knew packets were lost.
What Real-Time Applications Actually Experience? Video calls, gaming, VoIP, and live streaming use UDP (User Datagram Protocol) — not TCP. UDP does not retransmit. If a packet is lost, it's gone. There's no second chance. Packet 1 → ✓ received Packet 2 → ✗ lost forever Packet 3 → ✓ received Packet 4 → ✗ lost forever Packet 5 → ✓ received UDP result: 40% packet loss. "Your connection has a real problem." This is why your Speedtest looks perfect but your Zoom call is freezing — the test and the application are speaking completely different protocols.
How to Actually Measure Packet Loss? To measure what real-time applications experience, you need a tool that uses UDP. I built https://networktests.com to solve exactly this problem. It uses WebRTC DataChannels configured in unreliable/unordered mode — which gives UDP semantics directly in the browser. No install, no plugin, no signup required.
It measures: - Packet loss — the percentage of packets that never arrive
- Latency — round-trip time, plus p95 tail latency - Jitter — variation in latency over time (the hidden cause of choppy calls)
Hop-by-Hop Path Diagnostics Beyond the core test, NetworkTests.com also runs hop-by-hop path diagnostics — similar to MTR (My TraceRoute) — from our servers back to your connection edge.
This uses STUN-assisted UDP to traverse NAT and perform inbound path analysis directly from a browser session. Each router hop between our server and your connection is probed individually, revealing exactly where packet loss or latency is introduced on the path. This is unusual for a browser-based tool — most tools can only measure outbound paths, not inbound.
Reading Your Results
┌─────────────┬───────────┬────────┬──────────┬─────────┐
│ Metric │ Excellent │ Good │ Fair │ Poor │ ├─────────────┼───────────┼────────┼──────────┼─────────┤
│ Packet Loss │ < 0.1% │ < 1% │ 1–2.5% │ > 2.5% │ ├─────────────┼───────────┼────────┼──────────┼─────────┤
│ Latency │ < 20ms │ < 50ms │ 50–100ms │ > 100ms │ ├─────────────┼───────────┼────────┼──────────┼─────────┤ │ Jitter │ < 2ms │ < 5ms │ 5–15ms │ > 15ms │ └─────────────┴───────────┴────────┴──────────┴─────────┘
A connection with 0% packet loss on Speedtest but 3% on a UDP test has a real problem — one that affects every video call and game you play.
Other Tools Included: NetworkTests.com also includes a suite of diagnostic tools:
- DNS Lookup — query A, AAAA, MX, TXT, CNAME records - DNS Trace — trace the full resolution chain from root nameservers - DNS Leak Test — verify DNS queries aren't bypassing your VPN tunnel - VPN Detection — confirm your connection is actually routed through a VPN - SSL Proxy Check — detect TLS interception via ClientHello fingerprinting - Traceroute / MTR / Ping — standard path diagnostics - IP Lookup, AS Lookup, Reverse DNS, MAC Lookup All free, all in the browser.
Conclusion:
TCP speed tests are useful for measuring raw throughput — but they're blind to the problems that actually affect your daily internet experience.
If your video calls drop, your games lag, or your VoIP sounds bad — run a UDP test. The results might surprise you. https://networktests.com
https://networktests.com/about
Have you ever had a connection that passed every speed test but still felt broken? What did you end up finding?
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