Game Lag White Paper › L2 Client OS and device

Wi-Fi background scanning Periodic Wi-Fi background scan

Cause ID co-wifi-scan · Primary owner External (External) · Also Game team (Client development)

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Communication pauses briefly while the OS periodically hops across channels to look for nearby Wi-Fi networks.

Why The OS or driver searches for nearby Wi-Fi networks on a fixed schedule → Effect Sending and receiving pause briefly during the scan → On screen Ping spikes at exactly regular intervals (e.g., every 60 s)

Symptoms

Stutter, Teleporting

Factors

Jitter

Who’s affected

Just me

When

At regular intervals

Owner

Primary owner External (External) · Also Game team (Client development)

Game team action items

Request a mode that reduces wireless scanning during play (on Android, the low-latency Wi-Fi mode WIFI_MODE_FULL_LOW_LATENCY; on Windows, the media streaming mode of WlanSetInterface; it may have no effect on some devices and drivers).

External action items

Tell players to use a wired connection, adjust location services and automatic Wi-Fi scanning settings, and update wireless drivers.

Ballpark numbers

Usually tens to hundreds of ms each time. If the spikes are suspiciously regular, suspect this first.

On the graph

Periodic spikes · RTT to the router

Where to look

During play, ping the router address (Default Gateway in ipconfig) with ping /t for a few minutes and measure the interval between spikes. Repeat the same measurement over a wired connection

Confirmed if

Ping to the router spikes by tens to hundreds of ms at exactly regular intervals (e.g., 60 s) and goes away on a wired connection

Ruled out if

Irregular spike intervals: “Wi-Fi interference and weak signal.” Fine up to the router but spiking beyond it: the connection or ISP segment

Check with

The player’s own environment

Sources

1. WDI low latency connection quality Microsoft
   Scanning and roaming move the radio off the connected channel, so low-latency mode limits scanning and time spent off-channel
2. WlanSetInterface function (wlanapi.h) Microsoft
   Windows API that turns background scanning (wlan_intf_opcode_background_scan_enabled) and media streaming mode on and off
3. Wi-Fi low-latency mode Android (Google)
   Low-latency mode turns off Wi-Fi power saving; how scanning and roaming settings are optimized depends on the device maker’s implementation
4. ping Microsoft
   /t: keeps sending echo requests until stopped
5. ipconfig Microsoft
   Run with no parameters, it shows each adapter’s IPv4 and IPv6 addresses and default gateway

See also

Same layer: L2 Client OS and device

• Background processes taking up CPU
• Power saving and thermal throttling
• Timer resolution
• Mobile app sent to the background
• Wi-Fi ↔ LTE/5G switching
• Packet inspection by security software
• Receive buffer overflow
• Client low on memory and swapping
• Out of graphics memory (VRAM)
• NIC power saving and driver issues
• Other apps on the same device using up bandwidth
• Throttling when the window is minimized or unfocused
• Overlay software interference
• Display, input device, and frame generation latency

Same symptom (Stutter), other layers

• Frame time spike L1 Client game process
• Client garbage collection L1 Client game process
• Synchronous loading and shader compilation on the main thread L1 Client game process
• Slow storage delays asset streaming L1 Client game process
• Rendering load from large crowds L1 Client game process
• Missing or too-short interpolation buffer L1 Client game process
• Excessive extrapolation (dead reckoning) L1 Client game process
• Fixed-timestep catch-up spiral L1 Client game process

View the interactive card with figures and simulations