Packet loss

Packet loss is the percentage of data packets sent across a network that never arrive at their destination, typically caused by network congestion, faulty hardware, wireless interference, or a link exceeding its capacity. It is usually expressed as a percentage of packets sent over a measurement window.

Packet loss differs from network latency in what it measures: latency describes how long delivery takes, while loss describes whether delivery happens at all, and the two often occur together since congestion that increases latency can also cause routers to drop packets once buffers fill. Protocols respond differently to loss: TCP retransmits lost packets, trading loss for added latency, while real-time protocols used for voice or video often simply drop the affected frame rather than retransmit it.

Packet loss matters because even small amounts can noticeably degrade real-time applications like voice or video calls, while the same loss rate might be barely noticeable in bulk file transfer, making the acceptable threshold highly application-dependent. NetFlow analysis and dedicated network monitoring both surface loss, and it is a standard component of quality of experience scoring alongside latency and jitter.