Websites and speed

Bufferbloat: calls lag when the network is busy

Bufferbloat is latency that network devices add when they hold too much data in their buffers. Calls and games lag while the network is busy.

Applies to: All current macOS versions. networkQuality needs macOS 12 Monterey or later.Checked: 29 October 2026

Symptoms

Large buffers in the router or modem. When the link is full, packets wait in a long queue. Each wait adds latency.
Uploads that fill the link. Upload capacity is often much smaller than download capacity, so an upload fills it quickly.
No queue management on the router. Smart queue management can keep queues short. Not all routers have it, or it is off.

Run networkQuality while nothing else uses the network. Write down the responsiveness.
```
networkQuality
```
Start a large upload or download on another device. Run the test again.
```
networkQuality
```
Compare the two results. A large drop in responsiveness under load shows bufferbloat.
For a simple test, ping a server while the upload runs. Watch the times rise.
```
ping 1.1.1.1
```
Press Control-C to stop ping.

Open the settings of your router. Look for SQM, smart queue management or a similar QoS setting.
If the router has it, turn it on. Follow the instructions of the router maker for the speed values.
If the router does not have it, schedule large uploads and backups for times when you do not make calls.
Pause cloud sync during important calls.
Ask your provider whether the modem or router supports queue management.

Kilobat's speed test reports latency under load. It rates bufferbloat as Low, Moderate, High or Inconclusive.
```
kilobat speedtest --json
```
Output addedLatencyMs and bufferbloat, with verdicts for calls and streaming.
Under 15 ms of added latency is Low. Under 60 ms is Moderate. 60 ms or more is High.
To find the app that uploads, sort live traffic by upload.
```
kilobat status --watch
```
With Pro and the network filter, you can block an app for the length of a call. See Test for call stutter.

Is bufferbloat a problem with my Mac?

Usually no. The large buffers are in the router, the modem or the provider's network. The Mac only shows the effect.

Does a faster plan fix bufferbloat?

Not always. More capacity can help, but queues can still fill when a transfer uses the full link.

Sources checked on 29 October 2026. Man pages are the ones installed with macOS; open one with man <name> in Terminal.