Packet Loss
Packet loss occurs when transmitted packets fail to reach their destination. Causes include congestion (buffer overflow), CRC errors (physical layer noise), and intentional drops (QoS policing, firewall rules). TCP retransmits lost packets automatically. UDP does not – the application must handle loss.
Definition
Packet loss happens when packets are dropped before reaching the receiver. Network-level causes: router buffer overflow during congestion (tail-drop or AQM), CRC failures from physical layer errors (bad cables, interference), TTL expiration (routing loops), and intentional policy drops (rate limiting, firewalls). Even 0.1% packet loss devastates TCP throughput because TCP interprets loss as congestion and reduces its sending rate exponentially. At 1% loss, TCP throughput drops to roughly 1/sqrt(loss_rate) of capacity. UDP applications (VoIP, gaming, video) experience loss as degraded quality rather than reduced throughput – missing voice packets cause gaps, missing video frames cause artifacts. FEC (Forward Error Correction) adds redundant data so receivers can reconstruct lost packets without retransmission, trading bandwidth for loss resilience.
Examples
- –ping -c 1000 host | grep 'packet loss' measures loss rate
- –mtr host shows per-hop packet loss
- –tc qdisc add dev eth0 root netem loss 1% simulates 1% loss for testing
Related Protocols
Related Terms
Congestion
Network congestion occurs when traffic exceeds link or buffer capacity, causing packet loss and increased latency. TCP congestion control algorithms (Cubic, BBR, Reno) dynamically adjust sending rate to avoid overwhelming the network. Persistent congestion degrades all traffic on the shared path.
Jitter
Jitter is the variation in packet arrival times. If packets arrive at inconsistent intervals (5ms, 12ms, 3ms, 20ms), jitter is high. VoIP and video streaming are sensitive to jitter – inconsistent delivery causes choppy audio and video stuttering. Jitter buffers smooth out variation at the cost of added latency.
Retransmission
TCP retransmission resends packets that were lost or not acknowledged within a timeout period. Fast retransmit triggers after 3 duplicate ACKs (indicating a gap). Timeout-based retransmission (RTO) fires after a calculated delay. Excessive retransmissions indicate network congestion or path problems.