When the retransmission rules you built on top of UDP are too conservative, recovery is slow; when they’re too aggressive, they clog the connection even more.
Why Retransmission interval, retry count, and window size don’t suit the connection → Effect Slow recovery, or duplicate sends that make congestion worse → On screen Skills not going off, fast-forward, worse lag during congestion
Primary owner Game team (Server development) · Also Game team (Client development)
Game team action items
Server: base retransmission on measured round-trip time, separate channels by importance. Client: apply the same retransmission and channel settings as the server.
On the graph
Random spikes · Reliable UDP retransmission rate, in-game RTT
Where to look
Per-connection statistics from the library in use (retransmissions, estimated round-trip time, retransmission timeout), logged on server and client and compared with the same player’s actual connection loss rate (measured with mtr)
Confirmed if
Retransmission rate several times the actual loss rate: settings too aggressive. Retransmission timeout several times the measured round-trip time: settings too conservative
Ruled out if
Retransmission rate close to the loss rate and timeout in line with round-trip time: not a settings problem. Look at the connection loss itself
Check with
Game server or client logs and metrics
Sources
RFC 8085: UDP Usage GuidelinesIETF Retransmissions can add to congestion, so they fall under congestion control; round-trip time is estimated as an average of several measurements (EWMA), initial value 1 s, lower the sending rate when the timer expires