Game Lag White Paper › L3 Home network

RRC state transition delay (mobile radio power saving) Radio state promotion (RRC)

Cause ID hn-rrc · Primary owner Game team (Client development)

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When a phone has no traffic for a while, it drops its radio connection to a low-power state, and the next packet is delayed while it powers back up.

Why After a short period with no traffic, the phone puts its radio connection into a power-saving state → Effect To send the next packet, the connection has to be brought back up → On screen Only the first action after standing idle is noticeably slow

Symptoms

Input lag

Factors

Latency

Who’s affected

Just me

When

After sitting idle

Owner

Primary owner Game team (Client development)

Game team action items

Keep the radio active with light periodic traffic (at a cost in battery life).

Ballpark numbers

LTE usually drops to power saving after about 10 seconds with no traffic, and coming back takes tens to hundreds of ms (measured example: about 0.3–0.6 s). On 3G it’s over 1 second.

On the graph

Outliers only · RTT of the first request after idle (mobile)

Where to look

Break down in-game RTT by the gap since the previous traffic. On mobile, compare the RTT of the first packet sent after more than 10 s of idle with that of packets sent back to back

Confirmed if

On a mobile network, only the first packet after idle is hundreds of ms late, and packets sent right after it are normal. No difference on Wi-Fi

Ruled out if

Late even when sent back to back: the signal, connection, or route side

Check with

Game server or client logs and metrics

Sources

1. An In-depth Study of LTE: Effect of Network Protocol and Application Behavior on Performance (SIGCOMM 2013) ACM
   On the measured LTE network: power-saving transition timer (tail) 10 s, median delay to come back from power saving 435 ms (25th–75th percentile: 319–558 ms); 3G about 1.5–2 s
2. Optimize network access Android (Google)
   Radio state transition delay and tail time vary with the radio technology (3G, LTE, 5G) and carrier settings; 3G example: low power → full power about 1.5 s, idle → full power over 2 s
3. Report ITU-R M.2134: Requirements related to technical performance for IMT-Advanced radio interface(s) ITU
   Required control-plane latency from idle to active state: under 100 ms (excluding paging and the wired segment)

See also

Same layer: L3 Home network

• Wi-Fi interference and weak signal
• Congested Wi-Fi channel
• Bufferbloat (router queue)
• NAT mapping expiry
• Underpowered or overheating router
• Cell tower handover (while moving)
• Weak mobile signal and dead zones
• Frequent 5G↔LTE switching (at 5G coverage edges)
• Public Wi-Fi and corporate network restrictions

Same symptom (Input lag), other layers

• Rendering load from large crowds L1 Client game process
• Packet processing bottleneck on the main thread L1 Client game process
• V-Sync and the render queue L1 Client game process
• Power saving and thermal throttling L2 Client OS and device
• Other apps on the same device using up bandwidth L2 Client OS and device
• Display, input device, and frame generation latency L2 Client OS and device
• Propagation delay (physical distance) L4 Internet path
• Satellite internet (LEO/GEO) L4 Internet path

View the interactive card with figures and simulations