What is NTP in simple terms?

NTP (Network Time Protocol) is like a speaking clock service for devices connected to the Internet. It allows your phone, computer, and connected devices to ask specialized time servers, synchronized to atomic clocks, for the exact time.

Am I using NTP without knowing it?

Yes! Your Android or iPhone smartphone, your Windows, Mac, or Linux computer, your internet router, your GPS, and even your smart TV all use NTP automatically to stay on time. It is invisible and automatic.

What is the difference between NTP and NTS?

NTP transmits time without any particular protection. NTS (Network Time Security) adds a cryptographic security layer: your device can verify that the received time actually comes from the right server and has not been tampered with in transit.

An NTP pool is a group of time servers that work together. Instead of relying on a single server, your device can query multiple servers in the pool. If one goes down, the others take over. The most well-known is ntppool.org with over 4,000 servers worldwide.

Understanding NTP and NTS: The Simple Guide

By Richard DEMONGEOT | January 21, 2026 | Reading time: 10 min

What is NTP? (in 30 seconds)

NTP stands for Network Time Protocol.

Imagine a giant speaking clock on the Internet. Your phone, your computer, your router... all these devices regularly ask it: "What time is it exactly?"

This "speaking clock" is actually a network of time servers synchronized to atomic clocks — the most accurate clocks in the world, which only drift by one second every 300 million years!

How I use NTP without knowing it

Good news (or bad, depending on your perspective): you don't have to do anything! NTP works automatically on virtually all your connected devices.

📱

Android

Automatically synchronized via Google servers or your carrier

🍎

iPhone / iPad

Uses Apple servers (time.apple.com) automatically

💻

Windows

"Windows Time" service enabled by default (time.windows.com)

🖥️

Mac

Synchronized via Apple servers automatically

🐧

Linux

Uses chrony, systemd-timesyncd, or ntpd depending on the distribution

📺

Smart TV

Automatic time setting via Internet or broadcast signal

📡

Internet Router

Synchronized to your ISP's servers

🚗

GPS / Car

GPS satellites also transmit atomic time

How it works

The simple explanation (1 minute)

Your device asks for the time
Your phone sends a request to an NTP server: "What time is it?"
The server responds
The server responds with the exact time, synchronized to an atomic clock.
Offset calculation
Your device calculates the message's travel time and adjusts its own clock.
Regular repetition
This process repeats automatically (every few minutes to every few hours).

Want to see the 4 NTP messages in action? The animated 5-minute explainer on ntp-tester.eu visualises the request/response flow. And to diagnose a machine that does not synchronise correctly, check-ntp.net runs a live scan showing offset, latency and sync status in real time.

A bit more detail (for the curious)

The NTP protocol is organized into hierarchical levels called "Stratum":

            Stratum 0 — Atomic clocks, GPS, radio signals
            
The ultimate source of time (cesium, GPS, etc.)
        
            Stratum 1 — Servers directly connected to atomic clocks
            
Accuracy: a few microseconds
        
            Stratum 2 — Servers synchronized to Stratum 1
            
What most businesses use
        
            Stratum 3+ — Your devices (PCs, phones, servers...)
            
Synchronized to Stratum 2

👉 Go deeper: read our dedicated guide NTP Stratum Levels Explained: From Stratum 0 to 16 — accuracy per level, Stratum 1 vs Stratum 2 comparison, and how to check a server's stratum.

What is NTS? (the secure version)

NTS stands for Network Time Security. It is an evolution of NTP that adds a cryptographic security layer.

Classic NTP

Like a postcard

Time is sent "in the clear"
No sender verification
Someone could modify the message

NTP with NTS

Like a sealed registered letter

The exchange is authenticated (TLS 1.3)
The server's identity is verified
Impossible to tamper with the message

Learn more about NTS and how to enable it →

NTP Pools: Strength in Numbers

Main pools and public servers

Provider	Address	Specifics
Global NTP Pool	pool.ntp.org	Community-run, 4000+ servers
France NTP Pool	fr.pool.ntp.org	~370 French servers
Google	time.google.com	Leap smearing (smooth leap second handling)
Cloudflare	time.cloudflare.com	Supports NTS
Apple	time.apple.com	Used by iOS/macOS
RDEM Systems	ntp-pool.rdem-systems.com	11 servers, NTS enabled, France

For whom? Why does it matter?

👤 Individuals

You don't have to do anything! Your devices are already configured. NTP ensures that your emails arrive with the correct timestamp, that your 2FA codes work, and that your photos are correctly dated.

🏢 Businesses

Consistent time is crucial for:

Security log correlation
Transactions and billing
Compliance (GDPR, PCI-DSS...)
Proxmox clusters and NTP synchronization on Proxmox VMs
MariaDB replication and Galera cluster — replication lag detection (Seconds_Behind_Master) and Galera certification depend on synchronized clocks between nodes

🏭 Industry

Industrial systems (SCADA, PLCs) require precise synchronization to coordinate manufacturing processes and ensure traceability.

🏦 Finance

Financial markets require microsecond-level timestamping. MiFID II mandates 100-microsecond accuracy for high-frequency trading.

Going further

The Speaking Clock — hear NTP "for real" — a free, phone-accessible audible demo of the Stratum 1 time discussed in this article.
Our NTP infrastructure since 2005 — how these theoretical concepts translate into 20+ years of real-world operation.

Free NTP Tools

Three independent tools to diagnose your time synchronization: