# What is Packet Loss?

> Packet loss is the failure of one or more transmitted packets to arrive at a defined destination within a stated waiting period.

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## Content

It may be measured one-way or round-trip and expressed as a count or proportion. The definition must identify the endpoints, traffic type, timing threshold, and measurement interval.

Packets may be discarded because queues overflow during congestion, transmission errors occur, equipment fails, a route changes, or policy filters the traffic. Reliable transports may retransmit missing data, masking loss while increasing completion time; delay-sensitive or unreliable applications may expose it immediately.

### Key points

- **Measurement choice:** Use representative packet sizes, protocols, paths, and time windows. One-way tests require suitable clock synchronization; round-trip tests cannot reliably assign loss to the outbound or return direction.
- **Diagnostic context:** Correlate end-to-end loss with interface error and discard counters, queue utilization, route changes, radio conditions, captures, and application behavior before assigning a cause.
- **Service effect:** Even modest loss can reduce TCP throughput or degrade voice, video, gaming, and industrial messaging, depending on retransmission, buffering, redundancy, and application tolerance.
- **Important limitation:** Missing probes do not by themselves prove packet loss or malicious interference: filtering, rate-limited replies, asymmetric paths, sampling, and capture drops can produce similar evidence. Authorize and rate-limit active tests, especially on safety- or availability-sensitive operational technology (OT) networks.

### Related terms

[Network latency](<https://yellowcube.eu/glossary/network-latency/>) · [User Datagram Protocol (UDP)](<https://yellowcube.eu/glossary/user-datagram-protocol/>) · [TCP/IP protocol suite](<https://yellowcube.eu/glossary/tcp-ip-protocol-suite/>) · [Quality of service (QoS)](<https://yellowcube.eu/glossary/quality-of-service/>) · [Network traffic](<https://yellowcube.eu/glossary/network-traffic/>)

### Sources

[RFC 7680: A One-Way Loss Metric for IP Performance Metrics](https://www.rfc-editor.org/rfc/rfc7680) · [RFC 6673: Round-Trip Packet Loss Metrics](https://www.rfc-editor.org/rfc/rfc6673) · [NIST SP 800-82r3: Guide to Operational Technology Security](https://csrc.nist.gov/pubs/sp/800/82/r3/final)

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