protocols · 5 min read

What is NTP? Network Time Protocol explained

What is NTP? Network Time Protocol synchronises clocks across a network down to milliseconds. How does it work, and why do modern networks need it?

Network Time Protocol (NTP) is the protocol that keeps thousands of devices on a network on the same time, accurate to a few milliseconds. Without NTP, every server, switch, clock or camera runs its own internal clock that drifts, sometimes seconds per day. For logging, transaction ordering, video sync and compliance that is unusable.

What does NTP do, in one sentence?

NTP is like a postcard that every clock in your network sends out asking: "what time is it on your side?". The server replies with a timestamp. The clock compares it to its own time, calculates the difference plus the network transit delay, and corrects itself.

Why do you need NTP, even if you don't think about time?

Audit trails line up: log files from different systems can only be compared once their timestamps are aligned.
Security: TLS certificates expire at a precise moment. Clocks that are out of sync reject or trust certificates incorrectly.
Compliance: regulation in finance (MiFID II requires 100 microseconds), broadcast (frame-accurate sync) and e-health requires demonstrable time synchronisation.
Distributed systems: databases, microservices, message queues, anything that relies on "happened before" relations needs clocks that agree.

How does it actually work?

NTP uses a hierarchy of strata:

Stratum 0: the source, an atomic clock, a GPS receiver, or GNSS. Not directly attached to the network.
Stratum 1: an NTP server that synchronises directly with a stratum 0 source (a Masterclock NTP100-GNSS, for example).
Stratum 2-15: servers and clients that synchronise to a stratum 1 (or higher-numbered) server. The further from the source, the less accurate.

A client sends a request packet with its own time. The server replies with four timestamps: receive, transmit, and the client-time info. From those the client calculates the offset (difference between clocks) and the roundtrip delay (network latency).

NTP vs PTP

NTP achieves millisecond accuracy (and on a LAN sometimes tens of microseconds). For sub-microsecond accuracy you need PTP (Precision Time Protocol, IEEE 1588). See our article NTP vs PTP for the comparison.

How does NTP-implementation work via Daylight?

As authorised Masterclock distributor, we have supplied NTP servers and NTP-driven clocks since 2014 to broadcasters, data centres, banks, hospitals and industrial customers. Which configuration you need depends on scale, environment and compliance requirements. Get in touch and we will give you independent advice.