If your game lags or your video call stutters only when someone else in the house is downloading, uploading or streaming, the likely cause is bufferbloat: data piling up in queues when your connection is busy. The fix is a router feature called smart queue management (SQM), which keeps those queues short. If your router supports it, it’s the fix to try first.

What bufferbloat is

Bufferbloat is the delay that comes from network equipment buffering too much data. When your connection is fully used, by a big download, a cloud backup or a video upload, packets arrive faster than they can leave. They wait in a queue, and every packet behind them waits too, including the small, time-sensitive packets from your game or call. The IETF’s description of the problem calls this bufferbloat-generated excess delay.

The result is what you notice: voice and video calls stutter and drop, and games lag. Your speed test can look perfect, because a speed test measures how much data gets through, not how long it waits.

How to test for it

You don’t need special software. OpenWrt’s guide lists several browser-based tests that measure latency under load and grade bufferbloat, including Waveform’s and Cloudflare’s speed tests.

The fix: smart queue management

Queue management decides which packets wait and for how long. Two IETF-documented algorithms do the heavy lifting in most home routers that support it:

  • CoDel controls queue delay directly. It aims to keep persistent queue delay around a 5 ms target and needs no configuration in normal use.
  • FQ-CoDel adds per-flow queuing on top, so a big download gets its own queue and can’t crowd out the small packets from your game or call.
  • CAKE is another queue discipline, and the one OpenWrt prefers for mitigating bufferbloat; fq_codel is lighter if your router’s processor is weak.

There’s one catch. A queue forms at the slowest point, which is usually your internet connection, inside your provider’s or modem’s equipment, where your router can’t manage it.

OpenWrt’s guide gives a practical starting point: set the download and upload limits to 90% of the speeds you measured, then raise them and retest until bufferbloat comes back, and settle just below that point.

QoS is not the same as SQM

Many routers advertise “QoS” or gaming modes that prioritise game traffic. That can help, but it’s a different tool. ASUS, for example, describes its gaming mode as increasing the traffic weight of game packets, and notes that these features don’t increase total bandwidth; they help use existing bandwidth more efficiently.

What providers are doing

Some of the fix is moving into provider networks. CableLabs’ Low Latency DOCSIS targets round-trip latency below 5 ms in the cable network, 99% of the time, for traffic that doesn’t build queues, and DOCSIS 3.1 modems can be upgraded to it with software. Whether you benefit depends on your provider deploying it.

If it isn’t bufferbloat

If latency is high even when the connection is idle, or the lag doesn’t line up with other people’s usage, the cause is elsewhere: weak or crowded Wi-Fi (see Slow Wi-Fi), two routers in a row (see Double NAT), or simply a long distance to the game server. If you’re wondering whether a “gaming router” would help, read Do you need a gaming router? first.