What is Network Time Protocol (NTP)?
Network Time Protocol (NTP) is an essential component of modern networking, ensuring precise synchronisation of clocks across systems, whether over local networks or the internet.
Developed in the 1980s by Dr David Mills at the University of Delaware, NTP is one of the oldest networking protocols still in active use. Its fundamental aim is to align all participating devices to Coordinated Universal Time (UTC), thereby making operations reliable and keeping data integrity across networks. It’s worth noting that Dr Mills, who passed away in January 2024, is fondly remembered as the internet’s “father time” for his work on NTP.
Imagine a logistics company with depots worldwide: accurate time synchronisation is critical to ensure shipments are tracked, scheduled, and delivered without discrepancies. Without an algorithm such as NTP, operations could create costly errors and inefficiencies.
In this article, we briefly explain the fundamental concepts, architecture, and importance of NTP for allowing precise time synchronisation across networks. For more technical information, NTP is fully described in RFC 5905.
NTP architecture helps distribute precise time
At the core of NTP is a hierarchical structure of time sources, known as strata, designed to maintain high accuracy and redundancy. This architecture provides a robust way to distribute precise time even in the face of network issues or server failures.
- NTP servers and clients: NTP is intrinsically a client-server algorithm, where servers provide time data, and clients synchronise themselves to this time reference.
Additionally, it can work in peer-to-peer configurations where devices can serve both roles (server and client). - Stratum levels: NTP's hierarchy consists of strata, with each level representing the distance from a reference clock, typically a very accurate time source.
- Stratum 0: These are high-precision devices such as atomic clocks, GPS receivers, or radio clocks. They act as reference clocks but do not directly connect to the network, instead they link to stratum 1 servers.
- Stratum 1: These servers, known as primary time servers, discuss directly with stratum 0 devices to offer precise time to lower-strata devices.
- Further layers, such as stratum 2 and beyond, synchronise with higher-level servers, ensuring precision even in a node failure appears. This architecture is creating a reliable chain of time distribution.
How does NTP work?
NTP’s operational methodology involves accurate time distribution and complex checks to mitigate errors due to network latency, routing asymmetry, or inconsistent time sources.
- Time synchronisation process: NTP clients periodically communicate with multiple servers to receive timestamps. The protocol applies corrections to account for network delays and variations, ensuring that the client clocks gradually adjust towards a precise time reference. This gradual adjustment avoids time jumps that could disrupt critical operations.
- Server selection and reference clocks: Selecting the most accurate time source is not a trivial task. NTP uses the so-called Marzullo algorithm (named after Keith Marzullo, who invented it during his PhD at Stanford) to evaluate multiple time signals, ensuring the most reliable source is used.
For instance, if several servers provide time data, NTP verifies and averages their timestamps, thus reducing discrepancies and enhancing accuracy. Reference clocks, often external stratum 0 devices like GPS, serve as benchmarks for synchronisation. - Security considerations: Ensuring the authenticity and reliability of NTP servers is of the utmost importance. NTP incorporates built-in checks and safeguards to verify that the time source is legitimate. The goal is to avoid malicious sources that could disrupt synchronisation or compromise network integrity (by chance or intentionally).
NTP plays a key role in networks
NTP’s role in maintaining synchronised networks is critical for data consistency, security, and operational efficiency.
- Data transmission and integrity: Accurate timestamping is the key behind transaction logging, authentication, and data integrity in systems ranging from financial trading to database replication. Consider a high-frequency trading platform where milliseconds can determine profit or loss; NTP ensures that all events occur in the correct sequence, leaving no room for financial or legal disputes.
- Network security and timestamps: Time synchronisation is also pivotal for network security, where discrepancies can undermine protocols and certificate validation. For example, session tokens and digital certificates depend on precise time alignment to function correctly; a skewed clock can lead to rejected connections or security breaches.
- Global internet time synchronisation: NTP connects networks to public servers to maintain time consistency worldwide, ensuring smooth operations and communications.
NTP’s influence extends far beyond synchronising clocks; it also plays a pivotal role for ensuring consistency, accuracy, and security in any technical system made of several devices discussing over a network.
PTP versus NTP: an alternative time protocol
NTP is not the only existing time protocol. When a higher level of time precision is needed, Precision Time Protocol (PTP) is the alternative to NTP.
Introduced under the IEEE 1588 standard, PTP achieves microsecond and even nanosecond accuracy, making it indispensable for industries such as telecommunications, high-frequency trading, and industrial automation. Unlike NTP's stratum-based hierarchy, PTP employs a master-slave architecture with mechanisms like the Best Master Clock Algorithm (BMCA) to dynamically select the best time source.
PTP’s ability to reduce network latency through features like boundary and transparent clocks sets it apart. However, NTP remains more straightforward to deploy and sufficient for most network synchronisation needs. This makes it a reliable choice for many applications.
