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Congestion Test: Find Hidden Network Bottlenecks
Network congestion shows up not as a single broken metric but as a pattern: latency rises with load, packet loss appears at higher offered rates, and throughput plateaus below your nominal speed. The Congestion Test detects these patterns to tell you whether congestion is upstream of you, in your home, or absent.
What It Measures
This tool measures network congestion by progressively increasing offered load while tracking latency, throughput, and loss. The shape of the curves identifies the type of congestion: bottleneck queue (latency rises, then loss), AQM (loss rises gradually), or rate cap (throughput plateaus cleanly).
How It Works
- Sends progressively larger waves of TCP traffic to an edge server
- Samples latency and packet loss at each load level
- Identifies the load level where latency or loss begins to climb
- Classifies the congestion pattern (queueing, AQM, hard cap) and locates it
Why It Matters
Knowing why a connection slows down matters as much as knowing that it does. Bufferbloat from a fat queue calls for SQM. ISP rate capping requires a plan upgrade. Random loss often means cable or wireless issues. The congestion pattern points to the right fix instead of generic troubleshooting.
Understanding Your Results
Latency that stays flat as load increases up to your nominal speed indicates good queue management or a high quality AQM. Latency that climbs steadily indicates bufferbloat. A sharp throughput plateau at your plan speed is normal. Loss appearing only at very high load and remaining low is healthy.
Frequently Asked Questions
What is the difference between congestion and throttling?
Congestion is unintentional, caused by too much traffic competing for limited capacity. Throttling is intentional, caused by an ISP applying rate limits to specific traffic. Congestion symptoms vary by time of day and load; throttling symptoms are consistent and often target specific destinations like streaming services.
What is AQM?
AQM (Active Queue Management) is a router behavior that drops or marks packets early to keep queues short. Algorithms like CoDel, fq_codel, and CAKE prevent bufferbloat by signaling congestion to senders before queues fill. Routers with AQM show much better latency under load than routers using simple drop tail queues.
Where is the congestion in my network?
Test results showing congestion that appears only during peak hours typically indicate ISP infrastructure congestion. Congestion that appears whenever your connection is loaded points to your home gateway. Congestion only on specific destinations suggests congestion at a peering point or transit provider rather than your direct link.
How can I reduce congestion?
On your network, enable SQM or fq_codel on your router to manage local queues, and prefer wired Ethernet for latency sensitive applications. ISP side congestion may require a plan upgrade, switching providers, or using a CDN that peers more directly with your ISP. Time of day congestion sometimes resolves by simply shifting heavy use outside peak hours.
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