Netnod’s White Rabbit implementation uses bi-directional transmission to achieve sub-nanosecond accuracy over a high accuracy fibre link between two Netnod time nodes in Stockholm and Sundsvall, a distance of about 440 km.
“This is an important moment for Netnod and part of our ongoing commitment to developing the most accurate and secure time services possible,” said Patrik Fältström, Technical Director and Head of Security, Netnod.
While many time services today rely on the Global Navigation Satellite Systems (GNSS), such as GPS, Glonass, Galileo and Beidou, GNSS can have serious issues. These include signal interference, unpredictable latency and vulnerability to attack using signal jamming and spoofing. Precision Time Protocol (PTP) services connected to atomic clocks were designed to provide an alternative form of high accuracy synchronisation. But when connecting a master atomic clock to the different nodes of a network over long distances, time accuracy can suffer.
White Rabbit was developed to fix this and to enable Ethernet networks to achieve sub-nanosecond accuracy over a large area. Originally developed at CERN to synchronise the measurement and control equipment of particle accelerators and detectors, White Rabbit builds on the PTP / IEEE 1588 and SyncE (Synchronous Ethernet) standards, currently the most advanced standards for high accuracy time synchronisation.
Netnod’s White Rabbit implementation was tested in cooperation with the Swedish National Research and Educational Network, SUNET. The implementation was adapted to work in parallel with the equipment SUNET uses on the same fibre links. Running White Rabbit wavelengths on the side of SUNET’s DWDM network, Netnod saw a far better performance than using a fibre link based on the traditional PTP setup.
Summarising the technical setup Netnod used to implement White Rabbit, Ragnar Sundblad Systems Specialist, said: “Using bi-directional transmission helped us increase accuracy by avoiding time errors due to cable length asymmetries. This meant we couldn’t use the equipment in SUNET’s optical network. We had to run wavelengths on the side of the SUNET DWDM equipment and use separate amplifiers. So we needed to work with suppliers to get custom built wavelength filters and optical interfaces.”
In addition to achieving sub-nanosecond accuracy, Netnod’s implementation also automated many of the processes used for different kinds of calibrations.
“We set up a calibration rig with instruments and cabling, used fibre switches to automate switching between different fibre links, and automated the communication and calculations,” said Sundblad. “With this level of automation, we can calibrate iteratively to achieve even better accuracy.”
The development of White Rabbit opens up many important possibilities. These include a high-accuracy alternative to GNSS, a way to effectively monitor GNSS function, and the possibility of deploying many local time nodes. When fully developed, a White Rabbit implementation enables networks to run tens of thousands of nodes all based on the same master clock. By enabling an Ethernet network to achieve sub-nanosecond accuracy, White Rabbit has significant value for a range of commercial and research sectors.
More information on Netnod’s White Rabbit implementation is available in a recently published blogpost here.
Netnod’s Network Time Protocol (NTP) and PTP services offer a robust, reliable and highly accurate source for time and frequency. Netnod has also played a leading role in developing the new standard and implementations for Network Time Security (NTS).
More information about Netnod’s time and frequency services is available here.
Netnod provides robust and traceable time and frequency services on behalf of the Swedish Post and Telecom Authority to make Sweden more resilient and better equipped for the future.
Netnod provides critical infrastructure support ranging from interconnection services and Internet Exchanges to time services, DNS services and root server operations. With a worldwide reputation for its services and the expertise of its staff, Netnod ensures a stable and secure Internet for the Nordics and beyond. Established in 1996 as a neutral and independent Internet infrastructure organisation, Netnod is fully owned by the non-profit foundation TU-stiftelsen (Stiftelsen för Telematikens utveckling). More information is available at: www.netnod.se