Gaming

In short: In a network context: online games that need continuous, latency-critical data exchange between client and server (or between players).

In more detail: Gaming traffic places special demands on a network — low latency usually matters more than high bandwidth, since input has to be processed in real time. Many games use UDP instead of TCP, because a lost, slightly outdated packet does less harm than the wait for retransmission that TCP forces.

In Depth

The core conflict with online games: TCP guarantees that every packet arrives in the right order and completely — if one is lost, the entire transfer waits until it’s resent and acknowledged. For a position update in a game, which is resent every few milliseconds anyway, this guarantee is usually worthless: a 100-millisecond-old, lost position update isn’t worth resending any more once a newer one has long since arrived. That’s why most real-time multiplayer games rely on UDP, which simply ignores packet loss, and build their own lightweight reliability layer on top when needed, applying only to critical events (e.g. “player fired a shot”).

Besides low latency, “jitter” also plays a role — the fluctuation of latency from packet to packet. A consistently high latency of 80 ms is more playable for many games than an on-average lower but strongly fluctuating latency between 20 and 150 ms, because games often slightly “buffer” the arrival of updates to smooth out such fluctuations.

See also: UDP, Latency, Real-Time Application