Why bufferbloat gets worse during uploads

Your upload starts, and suddenly a video call freezes or a game becomes laggy. The internet may still be transferring data quickly, but small, time-sensitive requests are waiting behind the upload.

This delay is often bufferbloat. It happens when network equipment queues too much data before sending it. The Bufferbloat Test compares delay while the connection is idle and under download or upload load, so you can see whether a full upload is the trigger.

Test bufferbloat during an upload

1. Open the Bufferbloat Test and run the test with other downloads and uploads paused. This gives you a cleaner baseline.
2. Note the idle delay and the test grade, which runs from A+ to F.
3. Run the test again while a large file is uploading, or while a cloud backup or video upload is active.
4. Compare how much the delay rises under upload load with the idle result. If you can, repeat once with the upload paused to check that the change follows the upload.

The test exchanges test data with our server to measure the connection. It does not need access to your personal files. For a useful comparison, keep the same device, browser and network connection for each run.

What the result means

The delay rises sharply during upload

Your connection is likely building a long queue somewhere between your device and the internet. When that queue fills with upload data, interactive traffic such as game packets, voice and acknowledgments for downloads can wait. The connection can still show a good upload speed while feeling unresponsive.

A poor grade points to a noticeable increase in delay under load. It does not by itself identify whether the queue is in your router, modem or farther along the connection.

The upload barely changes the delay

There is little evidence of severe upload-related bufferbloat in this run. If calls or games still stutter, check for Wi-Fi interference, packet loss, a busy device or an issue with the app. A single test is a snapshot, so run it again when the problem is happening.

The delay rises only on Wi-Fi

Some of the extra delay may come from the wireless connection rather than a queue at the internet connection. Wi-Fi interference and a weak signal can cause waiting and retries. Repeat the test close to the router, or connect by Ethernet if possible, and compare.

The delay rises even when you pause the upload

Another device or app may still be using the connection, or the issue may be unrelated to upload load. Check for cloud backups, security camera uploads, game updates and other people using the network. Then retest at a quieter time.

How to reduce upload-related delay

1. Pause the largest upload. Stop cloud backups, file transfers or video uploads while you need a call or game to stay responsive. If the delay drops immediately, you have confirmed that upload load is part of the problem.
2. Limit the upload speed in the app. Some backup, sync and transfer apps let you set an upload limit. Start around 85 to 90 percent of the upload speed you measured, then run the bufferbloat test again. Leave enough capacity for other devices and increase the limit gradually if the delay stays low.
3. Turn on smart queue management in the router. Look in the router's settings or documentation for Smart Queue Management, SQM, CAKE or fq_codel. These features manage the queue so one large transfer is less likely to hold up small packets. A simple priority or Quality of Service setting may help, but it does not always control queues as well as SQM.
4. Set a realistic upload limit on the router. If SQM asks for upload capacity, enter a little less than the speed your connection reliably achieves, not a higher advertised plan speed. Retest and adjust in small steps. A setting that is too high can leave the queue unmanaged, while one that is too low unnecessarily slows transfers.
5. Compare Ethernet with Wi-Fi. Connect the test computer to the router with Ethernet and repeat the same test. On Windows 11, check the connection under Settings › Network & internet. On macOS, check System Settings › Network. If Ethernet improves the result, work on the wireless link as well as the router's upload queue.
6. Restart and update your network equipment. Restart the modem and router if the delay remains unusually high, then check the manufacturer's instructions for firmware updates. Retest after each change so you know what helped.

Why uploads can cause more trouble than downloads

Many home connections can download data faster than they can send it. That makes the upload link a narrow point in the path. When an app tries to send data faster than that link can carry it, the modem or router stores packets in a queue and sends them in turn.

Some packets are small but urgent. A voice packet, a game update or a confirmation that received data arrived can end up waiting behind a large stream of upload data. The waiting time is added to the ping. If the queue is already long, adding more upload traffic can make the delay much worse, even though the connection has not disconnected.

Wi-Fi bars do not show how long packets wait in a queue. The Bufferbloat Test measures how the connection responds under load, not the Wi-Fi signal strength in dBm. Compare repeated runs under similar conditions, and treat the grade as a guide to loaded delay rather than a guarantee of how every app will perform.

If several devices share the connection, a single computer cannot always control the whole queue. Router-level queue management is usually the better fix when uploads from different devices regularly disrupt calls or games.