Network time synchronization is critical for many organizations. A robust source of accurate time is of utmost importance. Here are a few factors to consider when purchasing a commercial NTP server:
- Choice of reference clock, GPS or Multi-GNSS.
- Polling frequency and the number of network time clients that can be synchronized.
- Timing accuracy, how tightly an appliance can synchronize to UTC.
- Holdover, how long a device can maintain accurate time in the event of GNSS signal loss.
- Number of Ethernet ports in order to provide timing to multiple independent networks.
- Redundancy and peering to build a robust source of accurate time.
- Security features, such as SSH, SSL and authentication.
- Automatic leap second insertion.
Network Time Protocol (NTP) is used to synchronize the time of computer networks. It is one of the oldest and most widely used standard Internet Protocols (IP).
NTP coordinates the real-time clocks of servers and workstations to a reference clock with millisecond precision.
The protocol is also used by a wide variety of network devices including routers, switches, telephone systems, CCTV cameras and Digital Video Recorders (DVR).
With implementations available for most operating systems, NTP is widely adopted as the standard protocol for computer time coordination.
Many organizations require a robust and reliable source of accurate time for network timing. When buying a commercial NTP server, it is important to consider a number of factors to implement a robust network time synchronization service.
Synchronized Network Time Is Critical
The coordinated time of computer networks is critical to guarantee the correct sequencing of processes. It is also a vital requirement for correctly logging the time of events.
For many industries, accurate synchronization of computer systems is a legal requirement. For instance, financial trading systems are legally required to very precisely synchronize the real time clocks of their computers.
Many industries also require accurate time stamps to be applied to the occurrence of events. For example, pharmaceutical companies need to log exactly when batches of product are produced.
Security companies have a requirement to coordinate cameras with a legally traceable source of accurate time in order to prove when events took place.
Reference Clocks – GPS, GLONASS and Galileo
The Global Positioning System (GPS) has been the primary source of accurate time for a number of years.
The GPS system is usable from any location on the face of the Earth.
Reception ideally requires the installation of an antenna with a good view of the sky. Though, reception with a window mounted or even indoor mounted antenna can be feasible.
GPS provides consistent timing to nanosecond accuracy.
GLONASS is the Russian Global Navigation Satellite System (GNSS) alternative to GPS. It is less widely used than GPS, but provides a usable source of accurate time.
The new European Union Galileo GNSS system is now coming online. Similar to the GPS system it also provides world-wide signal coverage. Galileo provides timing to 30 nanoseconds.
Some NTP server appliances, such as TimeTools T550, provide multi-GNSS signal reception. They allow multiple satellite systems to be received concurrently. This provides an even more reliable system, since signals from independent satellite systems can be received and compared.
Multi-GNSS systems also provide an enhanced level of redundancy by accessing multiple separate satellite systems.
TimeTools T550 has an added advantage of allowing multiple satellite systems to be received from a single antenna.
The timing accuracy that can be achieved by a NTP server is largely dependent on its reference clock. The processing power of the server is also a factor.
Most satellite based reference clocks are accurate to a few tens of nanoseconds. Radio based reference clocks, such as MSF and DCF-77 are only accurate to tens of milliseconds.
The processing power of a device allows it to synchronize tightly to a reference clock. However, even a relatively low speed processor can synchronize to within a few microseconds, which is more than adequate for most applications.
NTP Polling Rate and Maximum Number of Clients
The maximum number of clients that a NTP appliance can serve is also dependent on the power of the devices processor. Faster processors have a higher potential polling rate, thus increasing the number of clients that it can synchronize.
The standard NTP client polling frequency is once every 64 seconds. So even a relatively low speed processor can server a large number of clients.
TimeTools T-Series NTP servers has a NTP polling rate in excess of 1500 NTP requests per second. This allows it to serve time to over 100,000 network time client computers.
Reducing the client polling rate increases the number of clients that can be served. Newer releases of NTP are utilizing 128 second client polling rates. At this rate a T-Series device can synchronize in excess of 200,000 clients, easily enough for the largest of networks.
Maintaining Time During Signal Loss – Holdover
A Stratum 1 NTP server relies on the availability of a hardware reference clock to maintain accurate time.
Some appliances have extremely stable Temperature Controlled Crystal Oscillators (TCXO) or oven-controlled crystal oscillators (OCXO) oscillators. These devices allow the device to maintain an accurate time for a much longer period in event of reference clock signal loss. This extended time period may be used to repair or replace a faulty antenna or damaged cable.
OCXO’s are very stable, but come at a cost. TCXO’s offer a much better price-performance compromise. TimeTools T550 incorporates a TCXO oscillator, which provides 2 parts per million (PPM) stability over 0C to 40C temperature range.
Additional Ethernet Ports
Many NTP server appliances, such as TimeTools T100 and T300, have a single Ethernet port. This provides synchronization for a single network.
TimeTools T550 has dual-Ethernet ports which allows two independent networks to be synchronized from a single device.
Redundancy and NTP Peering
The installation of a fully redundant time system is vital for many organizations.
Many commercial NTP servers have the ability to be peered together. This allows multiple devices to agree time. In the even that a device loses GPS/GNSS signal lock, it can still maintain accurate time from other peered servers.
NTP clients also have the ability to contact multiple servers. In the event that a server develops a fault, the client can automatically switch to a secondary server.
Network security is critical to most organizations. A NTP appliance can be installed inside a firewall. Therefore, ports do not need to be left open in the firewall for time synchronization communication. Keeping firewall ports closed reduces the potential of network security breaches.
Many NTP appliances can also implement authentication algorithms to prevent spoofing. Authentication is a mechanism that allows a client to verify the authenticity of a server.
Automatic Leap Second Insertion
NTP time servers should have the capability to correctly insert impending leap seconds. However, some devices require a leap second file to be uploaded before the leap second occurs, to ensure it is inserted correctly.
Most servers, including TimeTools T-Series devices, correctly warn of and insert leap seconds completely autonomously. No leap second file is required.
TimeTools T300 GPS NTP Server Appliance Features
- Unit Price from GBP 850.00 \ EUR 995.00 \ USD 1150.00
- GPS Referenced, Stratum-1, Network Time Server utilizing NTPv4 protocol.
- GPS timing accurate to 15nsec when locked.
- NTP timing to 3usec when synchronized to GPS.
- Ability to synchronize up to 100,000 NTP or SNTP clients at standard polling frequencies.
- Single 10/100 Mbit auto-sensing, auto-MDIX Ethernet port.
- Supports both IPv4 and IPv6 Internet Protocols (IP).
- Provided with weather-proof, permanent-mount, high-gain GPS antenna and mount.
- Integrated universal AC mains input for world-wide operation.
- High quality, UK made, with free lifetime support.
TimeTools T550 Multi-GNSS NTP Server Additional Features
- Unit Price from GBP 1150.00 \ EUR 1350.00 \ USD 1570.00
- Multi-GNSS receiver allows concurrent reception of GPS and either GLONASS, BeiDou or Galileo for improved reliability and redundancy.
- High-stability TCXO oscillator provides extended Stratum-1 holdover during loss of GNSS signal lock.
- Dual 10/100 Mbit auto-sensing, auto-MDIX Ethernet ports.
|About Andrew Shinton
Andrew Shinton is the joint founder and Managing Director of TimeTools Limited. He has a BSc (Hons) degree in Computer Science. Andrew has over 20 years experience of GPS systems and Network Time Protocol (NTP) in the Time and Frequency Industry.