Why ping goes up while something downloads, and how to check it

While a game or an update downloads, your in-match ping jumps by tens or hundreds of milliseconds. Usually that is a queue in the router or at the provider. Here is how to compare latency when idle, while downloading and while uploading, and what to do with the result.

The short answer

When the line is full of download traffic, packets queue up — in the router or at the provider. A small game packet waits for big chunks of the download to pass, and ping rises even though the server is no farther away. This is called bufferbloat. The IETF's recommendations say plainly that excess queueing means unwanted delay, and that queue management should keep queues short (RFC 7567). The check is simple: measure latency when idle, while downloading and while uploading, and compare.

The check in NyxBoost

In the released version 0.30.3 this is Latency under load: Network → Connection check tab → Check latency. It is free and changes nothing on your PC.

1. Pause whatever is downloading: Steam, torrents, cloud sync. Otherwise the “idle” phase is not idle.
2. Press Check latency. NyxBoost warns you first: about 21 seconds and up to 250 MB of traffic — worth knowing on a metered connection.
3. Wait for three phases: 5 s idle, 8 s of download in three streams, 8 s of upload in three streams. All the while NyxBoost sends short HTTPS requests to a Cloudflare test node and measures how long the replies take.

Cloudflare's own speed test works on the same principle — empty requests during the transfer (how it works).

What the result means

Three tiles: IDLE, WHILE DOWNLOADING, WHILE UPLOADING. Each shows the median in milliseconds, a high percentile (the 95th when there are enough replies) and “+N ms over idle”. NyxBoost calls it a spike when the median rises by at least 30 ms or the high percentile by at least 60 ms.

• “Latency barely rises under load”. The line copes. If you still lag, look at the game server or Wi-Fi interference — that is what Continuous ping is for.
• “Spikes while downloading”. A queue on the way in. The usual suspects are Steam downloads, torrents, Windows Update and HD video on other devices.
• “Spikes while uploading”. A queue on the way out: OneDrive, Google Drive, Dropbox, streaming, sending big files. On plans where upload is much slower than download it fills up sooner.
• “Spikes both while downloading and uploading”. Queues in both directions — the fix is in the router (below).
• “Latency jumps even while idle”. Downloads are not the issue: the line itself or Wi-Fi is unstable.

Latency is measured to a Cloudflare test node, not to your game's server, so the numbers themselves will differ. But the queue sits on your connection, so the extra delay under load hits every server.

Wi-Fi or cable

Run the check twice at the same time of day: over Wi-Fi and over an Ethernet cable. Which adapter is active and at what link speed is shown in Network → Connection, under ADAPTERS.

• Calm on cable but jumpy on Wi-Fi even when idle: it's the radio link. Microsoft suggests keeping the device close to the router and changing the wireless channel; the 5 GHz band often helps too.
• Spikes under load on cable as well: the queue is in the router or at the provider, not in Wi-Fi.

Latency to the router itself is shown by Check connection on the same tab. If the router alone already takes tens of milliseconds, NyxBoost tells you that this is usually Wi-Fi.

Windows background downloads

Windows downloads updates, Microsoft Store apps and Defender definitions through Delivery Optimization. Background downloads can be capped: Settings → Windows Update → Advanced options → Delivery Optimization — in megabits per second or as a percentage of the measured bandwidth. The cap applies only to automatic downloads, not to ones you start yourself (Microsoft's instructions).

You can also mark the connection as metered: then Windows Update downloads only priority updates and Microsoft Store downloads may pause. But that changes how other apps behave too, so a bandwidth cap is the more precise tool.

The router: SQM and QoS

If the queue is in the router, the most reliable fix is queue management — SQM (often based on FQ-CoDel) or QoS with a speed limit slightly below your plan. FQ-CoDel puts flows in separate queues, so small packets don't wait behind a big download (RFC 8290). Menu names depend on the firmware; if the router belongs to your provider, its owner changes the setting.

What not to expect: disabling Nagle's algorithm and network throttling for multimedia won't remove a queue in the router.

How the Premium speed test differs

The Speed tab has the Internet speed test (Premium). It measures download and upload speed, shows PING UNDER LOAD as one number — the worse of the two directions — with a grade of the latency increase, and keeps results in Measurement history. The free Latency under load check measures no speed, but splits the latency rise into download and upload and suggests a next step. To find the cause of your ping, the free check is enough.

Next step

Run the check as is, then with downloads and cloud sync paused, and once more on cable. Compare “+N ms over idle” across the three runs: where the extra delay disappears, there is your cause. If the game still stutters while the network is calm, frames are the more likely culprit — see stuttering at high FPS.