QoS policer
QoS mechanism: hard rate-limit. Traffic over limit is dropped (or marked down). Token-bucket algorithm. Standard use: ISP-level enforcement of paid bandwidth tier, DDoS mitigation, ingress rate-limit.
Distinct from shaper: policer drops, shaper buffers + delays. Single-rate vs two-rate (CIR + PIR — committed + peak info rate). Burst size controls token-bucket depth. Effect on TCP: packet drop signals congestion → senders back off → good fit for "smart" traffic. For UDP/real-time: policer can be catastrophic (jitter, audio glitches). Cisco MQC (Modular QoS CLI) standard config. Linux: tc police, or htb + drop policy.