# What is Network Latency?

> Network latency is the elapsed time for data to travel between defined points in a network.

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## Content

It may describe one-way delay from sender to receiver or round-trip time from sender to receiver and back. Meaningful results therefore state the direction, endpoints, packet type, and observation interval rather than reporting a number without context.

Delay can accumulate through propagation, transmission, processing, and queuing. It varies with route, load, link technology, packet size, and traffic handling. Averages can conceal spikes, so operations teams commonly examine percentiles and delay variation alongside representative application measurements.

### Key points

- **Measurement choice:** One-way measurement can reveal directional differences but requires adequately synchronized clocks. Round-trip measurement works from one endpoint without clock synchronization but combines both directions and the remote system’s response behavior.
- **Operational use:** Compare like-for-like measurements with a service baseline, correlate changes with path, utilization, loss, and application evidence, and test from locations that represent affected users.
- **Performance effect:** High or variable latency can slow interactive applications, delay acknowledgments, increase transfer time, and impair real-time voice or video even when link capacity is available.
- **Important limitation:** Latency is a performance observation, not proof of congestion, attack, or a particular faulty device. Active probes also add traffic; obtain authorization, rate-limit them, and follow site-specific safety-assessment and change-control requirements on operational technology networks.

### Related terms

[Packet loss](<https://yellowcube.eu/glossary/packet-loss/>) · [Quality of service (QoS)](<https://yellowcube.eu/glossary/quality-of-service/>) · [Wide area network (WAN)](<https://yellowcube.eu/glossary/wide-area-network/>) · [Network traffic](<https://yellowcube.eu/glossary/network-traffic/>) · [Traceroute](<https://yellowcube.eu/glossary/traceroute/>)

### Sources

[RFC 7679: A One-Way Delay Metric for IP Performance Metrics](https://www.rfc-editor.org/rfc/rfc7679) · [RFC 2681: A Round-Trip Delay Metric for IPPM](https://www.rfc-editor.org/rfc/rfc2681) · [NIST SP 800-82r3: Guide to Operational Technology Security](https://csrc.nist.gov/pubs/sp/800/82/r3/final)

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