NTP (Network Time Protocol) hardware refers to dedicated devices that provide accurate, traceable time to a computer network. Unlike software-based NTP clients, which synchronise to internet servers, NTP server appliances usually have their own GPS-based time source. Organisations use them where high accuracy, reliability, or security is critical such as finance, telecommunications, data centres, power, broadcast, and industrial systems.
Key Components
A number of components are critical to providing an accurate and reliable source of time using NTP.
Source Of Time
A reliable source of accurate time is essential to maintain precise and reliable time synchronization.
Global Navigation Satellite System (GNSS)
NTP server hardware often uses GPS or GNSS time sources, to provide precise and reliable time synchronization.
A GNSS receiver module obtains accurate time from orbiting satellites. Additionally, the receiver connects to an NTP server, typically a Linux host or dedicated time appliance. The NTP server uses the GNSS input as its Stratum 0 reference clock. Similarly, other network devices synchronize via NTP to that server and become lower stratum devices.
In short, the GPS (Global Positioning System) is the most common time reference, receiving precise UTC time from satellites. While, higher-end Multi-GNSS (Multi-Constellation) systems often support reception of GPS (US), Galileo (EU), GLONASS (Russia) and BeiDou (China) for redundancy. Importantly, GNSS receivers can receive signals while located anywhere in the world.
Radio Time and Frequency Broadcasts.
Radio time and frequency broadcasts are radio transmissions that carry precise time and frequency information, allowing clocks, navigation systems, and scientific instruments to stay synchronized with national or international time standards (like UTC).
Major time signal stations around the world include: WWV (Colorado, USA), MSF (Anthorne, UK), DCF-77 (Mainflingen, Germany) and JJY (Fukushima, Japan).
National metrology institutes that maintain atomic clocks are often responsible for the transmission of the radio timing signals. However, the radio signals are transmitted within national boundaries and reception can often depend on local geographical topology.
In contrast, most GNSS satellites transmit signals globally and are unaffected by geographical topology.
High Stability Oscillator (Internal Clock)
Computers have crystal oscillators (XO), that generate stable frequencies to keep time. However, they are very sensitive to temperature variation. Therefore, their system time will drift with temperature change.
In contrast, there are a number of much more stable oscillators available to maintain a more accurate time.
TCXO (Temperature Compensated Crystal Oscillator)
A TCXO is a Temperature-Compensated Crystal Oscillator. Engineers design this type of crystal oscillator to maintain a very stable output frequency over a wide range of temperatures.
A TCXO includes a temperature sensor that continuously monitors temperature. An electronic compensation circuit adjusts the oscillator’s control voltage to counteract any temperature-induced frequency drift.
In short, TCXO’s provide a great cost-performance trade-off.
OCXO (Oven Controlled Crystal Oscillator)
An OCXO is an Oven-Controlled Crystal Oscillator. They reduce frequency drift by enclosing a crystal, and often part of the control circuitry, in a temperature-controlled miniature oven. Importantly, the oven keeps the crystal at a constant, elevated temperature, typically around 60–85 °C. As a result, they are less affected by external temperature fluctuations.
In short, OCXO have better stability and drift performance than TCXO’s, but they are much more expensive.
Rubidium Oscillator
A Rubidium oscillator, often called a Rubidium frequency standard or Rubidium atomic clock, is a highly precise time and frequency reference device. It uses the natural resonant frequency of rubidium atoms to maintain an extremely stable output signal.
A basic Rubidium Oscillator Module can cost as much as USD 3,000, while a High-Performance Rubidium Frequency Standard can cost as much as USD 10,000. However, Rubidium oscillators have a rubidium lamp that degrades over time, with a typical lifespan of around 8 to 15 years.
In short, these high-cost oscillators provide amongst the highest accuracy and long-term holdover.
Network Interface
Network Time Protocol is a standard protocol for disseminating time to a network. Therefore, NTP hardware requires a network interface in order to connect to a network to synchronise client computers. Typically, systems use a 10/100 Mbps or gigabit (GbE) interface. Additionally, multiple Ethernet interfaces can be used for network segmentation or redundancy.
Supported Protocols
NTP appliances will need to support the Network Time Protocol in order to synchronize clients.
NTP has complex, advanced algorithms to handle jitter and packet round-trip delay compensation. While SNTP has much simpler algorithms which require far fewer calculations. Most servers will also support SNTP, Simple Network Time Protocol. In short, SNTP is a simplified version of NTP (Network Time Protocol), which synchronizes the clocks of computers and other devices over a network.
Furthermore, NTP has millisecond-level accuracy, ideal for servers, routers and critical systems. In contrast, SNMP accuracy is sufficient for IoT devices and simple embedded systems.
Support for TCP/IP and UDP is also necessary to implement NTP. While, configuration, management and monitoring require HTTPS, Syslog, SSH and SNMP protocols.
Security
NTP Authentication refers to the security mechanisms used in the Network Time Protocol (NTP) to ensure that time synchronization messages exchanged between clients and servers are genuine and unaltered. In contrast, without authentication, anyone could spoof NTP packets, potentially shifting system clocks.
In other words, NTP authentication ensures that the NTP client knows the server is legitimate and that no one has modified the message in transit.
How a Hardware NTP Server Works
A hardware-based NTP server operates in the following manner:
- Receives UTC from GPS or other sources.
- Disciplines the internal oscillator which keeps the device stable even if GNSS signals drop out.
- Distributes time to clients over the LAN using NTP.
- It acts as a Stratum 1 server, meaning it links directly to an authoritative UTC source.
- Clients synchronise typically as Stratum 2 devices from the Stratum-1 server.
Installation and Setup
Briefly, the installation and setup consists of:
- Installing an antenna. Ideally you should install a GPS/GNSS antenna with a clear 360 degree sky view.
- Use low-loss coaxial cable (e.g., LMR195 or LMR400) between NTP server and antenna.
- We recommend a lightning arrestor or surge suppressor for outdoor located antennas.
- Rack-mount device and connect.
- Configure via web or console interface.
- Set IP address, network mask and gateway and any required NTP parameters. Static IP recommended for predictability.
- Enable NTP service, configure authentication keys if needed.
- Connect clients.
- Point NTP clients to the server’s IP.
Best Practices
There are a number of Network Time Protocol (NTP) best practices to ensure accurate, secure, and reliable network time synchronization:
Install multiple NTP servers for redundancy.
Use at least 3 upstream hardware NTP servers to detect and correct anomalies.
Protect with firewalls and authentication.
Use symmetric keys to authenticate trusted servers. Also, allow only NTP UDP port 123 to/from known NTP peers. If possible, disable mode 6/7 control queries unless required.
Regularly check GPS signal strength and antenna condition.
Check GPS signal status information for a strong signal from multiple satellites. Ensure that any outdoor located antenna is in good condition and provides a good unobscured view of the sky.
Monitor via SNMP or Syslog for faults.
Use SNMP or monitor Syslog entries to ensure you consistently maintain synchronization.
Secure Your NTP Traffic.
Use restrict directives in the NTP configuration file to limit queries, control time service access.
Ensure firmware is up to date.
Check that you are utilizing the latest NTP firmware and GNSS reference clock drivers.
Additional Resources
https://www.ntp.org/support/vendorlinks
https://us.metoree.com/categories/2198/
Accurately and reliably synchronise the time on computers and network infrastructure in your organization with TimeTools TA-Series range of GPS and GNSS NTP time server appliances. We design and manufacture the TA-Series in the UK to provide:
- Advanced, GPS and Multi-GNSS Receivers For Reliable Reception Of The GNSS Satellite Systems.
- Security-Hardened, Enterprise-Class, Stratum-1 Operation.
- High-Performance For Precise Client Synchronization.
- High-Stability, Temperature-Compensated Crystal Oscillator (TCXO) For Extended Stratum-1 Operation In The Event Of Any Loss of GPS Signal Lock.
- Network-Optimized Gigabit Ethernet (GbE).
- Powerful, Easy To Use, Web Interface With Command Line Interface For Advanced Users.
- CE and UKCA Compliant With Full EMC and Electrical Safety Test Reports.