When the queue at the narrowest point fills up, such as a home router, a link between ISPs, or a data center uplink, newly arriving packets are dropped.
Why Video, downloads, and other users’ traffic fill up the bottleneck → Effect While the queue is full, newly arriving packets are dropped one after another (tail drop). Packets that get in wait at the back of the full queue → On screen Several packets vanish at once, causing a long freeze then fast-forward; common in the evening
Primary owner Infra team (Network infrastructure) · Also External (External), Game team (Client development)
Game team action items
Show network status on screen when losses cluster or ping spikes (mention that a large transfer on the same connection may be the cause).
Infra team action items
Keep headroom on data center links, check output drop counters on our links and switch ports, route around a congested ISP segment through another link or peering.
External action items
Tell players to use SQM (fq_codel, CAKE) and ECN on their router (so senders slow down before the queue overflows), ask the ISP to add capacity at the bottleneck.
Ballpark numbers
When a queue overflows, a large share of incoming packets can vanish at once over tens of milliseconds. Losing several packets in a row, and even losing the retransmissions, is common, so recovery often has to wait for an RTO.
On the graph
High at certain hours · Retransmission rate, RTT (ping)
Where to look
Server retransmission rate (TcpRetransSegs ÷ TcpOutSegs deltas from nstat run every minute) and per-connection RTT, split by region, ISP, and time of day, alongside output discards (ifOutDiscards) on our links and switch ports. Compare mtr runs to the affected region at peak and off-peak hours
Confirmed if
Retransmission rate rises only at evening peak, and RTT climbs just before the loss (the queue filling up). mtr shows loss and latency growing together from one hop to the end, only at peak hours
Ruled out if
No RTT rise before the loss points to “Policer drops excess traffic.” Similar loss at every hour points to “Physical errors (bad cable, optics, connectors)” or “Route change / bad ECMP path”
RFC 2863: The Interfaces Group MIBIETF ifOutDiscards: outbound packets discarded even though no error was detected, for example to free up buffer space
An Internet-Wide Analysis of Traffic PolicingGoogle Queue overflow raises queuing delay and RTT before the loss, while policing drops the excess with no RTT increase (SIGCOMM 2016)