White Rabbit Project

Last updated February 23, 2022

White Rabbit is the name of a collaborative project including CERN, GSI Helmholtz Centre for Heavy Ion Research and other partners from universities and industry to develop a fully deterministic Ethernet-based network for general purpose data transfer and sub-nanosecond accuracy time transfer. Its initial use was as a timing distribution network for control and data acquisition timing of the accelerator sites at CERN as well as in GSI's Facility for Antiproton and Ion Research (FAIR) project. The hardware designs as well as the source code are publicly available.^[1] The name of the project is a reference to the White Rabbit appearing in Lewis Carroll's novel Alice's Adventures in Wonderland .

Focus and goals

White Rabbit provides sub-nanosecond synchronization accuracy, which formerly required dedicated hard-wired timing systems, with the flexibility and modularity of real-time Ethernet networks. A White Rabbit network may be used solely to provide timing and synchronization to a distributed electronic system, or be used to provide both timing and real-time data transfer.^[2]^[3]

The White Rabbit Project focuses on:

Sub-nanosecond accuracy: synchronization of more than 1000 nodes via fiber or copper connections of up to 10 km of length.
Flexibility: creates a scalable and modular platform with simple configuration and low maintenance requirements.
Predictability and Reliability: allows the deterministic delivery of highest priority messages by using Class of service.
Robustness: no losses of high priority system device control messages.
Open source hardware and software: to avoid vendor lock-in.

Another characteristic of this project is that it operates completely on open source with both the hardware and software sources available.^[4]

Technologies

To achieve sub-nanosecond synchronization White Rabbit utilizes Synchronous Ethernet (SyncE) to achieve syntonization^[5] and IEEE 1588 (1588) Precision Time Protocol (PTP) to communicate time and a module for precise phase difference measurement between the master reference clock and the local clock based on phase frequency detectors.^[3]^[6]

White Rabbit uses the Precision Time Protocol to achieve sub-nanosecond accuracy. A two-way exchange of the Precision Time Protocol synchronization messages allows precise adjustment of clock phase and offset. The link delay is known precisely via accurate hardware timestamps and the calculation of delay asymmetry.

White Rabbit applications

At CERN White Rabbit was used for the new control system of the injector chain.

At GSI White Rabbit will become the timing system of the FAIR complex.

The KM3NeT neutrino telescope uses White Rabbit for synchronising the detector units.^[7]

The EISCAT 3D radar will utilise White Rabbit for synchronization in the beam forming network.^[8]

About 6000 detector nodes for the LHAASO (Large High Altitude Air Shower Observatory) experiment are synchronized by White Rabbit network.^{[ citation needed ]}

At least two Cosmic Microwave Background research programs (Simons Observatory, and CMB-S4) are considering White Rabbit for the timing of their data acquisition and control systems.^{[ citation needed ]}

Several companies^[9] have begun to commercialise White Rabbit for commercial applications by developing their own White Rabbit hardware and software.

The first white rabbit element on the white rabbit project was the "white rabbit switch", financed by the government of Spain and CERN, and produced by Seven Solutions.

In years 2015-2016 White Rabbit was successfully deployed by Horizon 2020 Project DEMETRA service #3 and tested for distribution Galileo precise UTC using ground fiber service.^[10]

A White Rabbit timing network

A white rabbit timing network consists of three important parts.^[11]

Precision Time Protocol - The IEEE1588 or the Precision Time Protocol is a time protocol designed to provide synchronization accuracy of 1 microsecond or even less, particularly for use in Industrial networks and Research labs where accurate synchronization is necessary. An accuracy of sub nanoseconds is ideally possible in PTP networks but, in practice, the master-slave and the slave-master links may be asymmetric and the resolution of the PTP time stamps is limited. Hence, the obtained synchronization accuracy in PTP networks is limited.
Layer I syntonization using SyncE - Just like the SyncE standard, the mechanism to operate all the nodes at the same frequency works at the physical layer level. Hence, there is no effect on data transfers because of this. The main idea of layer I syntonization is that the clocks in the network are not free running at a frequency, but instead, should be locked to a reference standard and be traceable. So, a network using Layer I syntonization has a hierarchy in the network: there is a master node which sends the frequency information in data streams and all other nodes in the system extract this information from the data stream and have a phase-locked loop which makes them run at exactly this frequency. This removes the jitter and frequency drift in the clocks that is responsible for the offset.
Phase measurement - As explained before, the frequency of the local node is disciplined using the clock signal extracted from the data stream sent by the master node. Then, the local node sends back its local clock signal to the master. As the local and master clock frequencies are locked, this clock signal is just a delayed version of the master clock signal. By calculating the phase offset between these two signals, a very accurate measurement for the particular link delay could be made.

After finding the link delay, this could be used in the conventional PTP algorithm to achieve a very high accuracy.

Components of a White Rabbit network are multi-port White Rabbit Switches and single or dual-port White Rabbit nodes. Both components may be added dynamically to the network. Cable length and other delay factors are automatically compensated by the Precision Time Protocol algorithms. Though conventional Gigabit Ethernet devices may be connected as well, only White Rabbit devices take part in network timing and synchronization.

Related Research Articles

Time and frequency transfer is a scheme where multiple sites share a precise reference time or frequency. The technique is commonly used for creating and distributing standard time scales such as International Atomic Time (TAI). Time transfer solves problems such as astronomical observatories correlating observed flashes or other phenomena with each other, as well as cell phone towers coordinating handoffs as a phone moves from one cell to another.

Clock synchronization is a topic in computer science and engineering that aims to coordinate otherwise independent clocks. Even when initially set accurately, real clocks will differ after some amount of time due to clock drift, caused by clocks counting time at slightly different rates. There are several problems that occur as a result of clock rate differences and several solutions, some being more appropriate than others in certain contexts.

The Precision Time Protocol (PTP) is a protocol used to synchronize clocks throughout a computer network. On a local area network, it achieves clock accuracy in the sub-microsecond range, making it suitable for measurement and control systems. PTP is currently employed to synchronize financial transactions, mobile phone tower transmissions, sub-sea acoustic arrays, and networks that require precise timing but lack access to satellite navigation signals.

Profinet is an industry technical standard for data communication over Industrial Ethernet, designed for collecting data from, and controlling equipment in industrial systems, with a particular strength in delivering data under tight time constraints. The standard is maintained and supported by Profibus and Profinet International, an umbrella organization headquartered in Karlsruhe, Germany.

Ethernet Powerlink is a real-time protocol for standard Ethernet. It is an open protocol managed by the Ethernet POWERLINK Standardization Group (EPSG). It was introduced by Austrian automation company B&R in 2001.

EtherCAT is an Ethernet-based fieldbus system invented by Beckhoff Automation. The protocol is standardized in IEC 61158 and is suitable for both hard and soft real-time computing requirements in automation technology.

Sercos III is the third generation of the Sercos interface, a standardized open digital interface for the communication between industrial controls, motion devices, input/output devices (I/O), and Ethernet nodes, such as PCs. Sercos III applies the hard real-time features of the Sercos interface to Ethernet. It is based upon and conforms to the Ethernet standard. Work began on Sercos III in 2003, with vendors releasing first products supporting it in 2005.

Reference Broadcast Synchronization (RBS) is a synchronization method in which the receiver uses the physical layer broadcasts for comparing the clocks. This is slightly different from traditional methods which synchronize the sender's with the receiver's clock.

Synchronous Ethernet, also referred as SyncE, is an ITU-T standard for computer networking that facilitates the transference of clock signals over the Ethernet physical layer. This signal can then be made traceable to an external clock.

High-availability Seamless Redundancy (HSR) is a network protocol for Ethernet that provides seamless failover against failure of any single network component. PRP and HSR are independent of the application-protocol and can be used by most Industrial Ethernet protocols in the IEC 61784 suite. HSR does not cover the failure of end nodes, but redundant nodes can be connected via HSR.

Parallel Redundancy Protocol (PRP) is a network protocol standard for Ethernet that provides seamless failover against failure of any network component. This redundancy is invisible to the application.

RTP-MIDI is a protocol to transport MIDI messages within RTP packets over Ethernet and WiFi networks. It is completely open and free, and is compatible both with LAN and WAN application fields. Compared to MIDI 1.0, RTP-MIDI includes new features like session management, device synchronization and detection of lost packets, with automatic regeneration of lost data. RTP-MIDI is compatible with real-time applications, and supports sample-accurate synchronization for each MIDI message.

Time-Sensitive Networking (TSN) is a set of standards under development by the Time-Sensitive Networking task group of the IEEE 802.1 working group. The TSN task group was formed in November 2012 by renaming the existing Audio Video Bridging Task Group and continuing its work. The name changed as a result of the extension of the working area of the standardization group. The standards define mechanisms for the time-sensitive transmission of data over deterministic Ethernet networks.

ALBEDO Telecom is a company that designs and manufactures products for the telecom industry including testers, synchronization nodes and networking devices. Typical users are R&D laboratories, Mobile and Telecom operators to verify and install the infrastructures that support any kind of applications based on voice, video and data. It is headquartered in Barcelona, Spain in the European Union.

Seven Solutions Spanish technology company

Seven Solutions is a Spanish hardware technology company headquartered in Granada, Spain, that developed the first white rabbit element on The White Rabbit Project which it was the White Rabbit Switch to use the Precision Time Protocol (PTP) in real application as networking. Seven Solutions got involved on it with the design, manufacture, testing and support.

IEC/IEEE 61850-9-3 or PUP is an international standard for precise time distribution and clock synchronization in electrical grids with an accuracy of 1 μs.
It supports precise time stamping of voltage and current measurement for differential protection, wide area monitoring and protection, busbar protection and event recording.
It can be used to ensure deterministic operation of critical functions in the automation system.
It belongs to the IEC 61850 standard suite for communication networks and systems for power utility automation.

Industrial automation systems consisting of several distributed controllers need a precise synchronization for commands, events and process data. For instance, motors for newspaper printing are synchronized within some 5 microseconds to ensure that the color pixels in the different cylinders come within 0.1 mm at a paper speed of some 20 m/s. Similar requirements exist in high-power semiconductors and in drive-by-wire vehicles. This synchronisation is provided by the communication network, in most cases Industrial Ethernet. Many ad-hoc synchronization schemes exist, so IEEE published a standard Precision Time Protocol IEEE 1588 or "PTP", which allows sub-microsecond synchronization of clocks. PTP is formulated generally, so concrete applications need a stricter profile. In particular, PTP does not specify how the clocks should operate when the network is duplicated for better resilience to failures.

Deterministic Networking (DetNet) is an effort by the IETF DetNet Working Group to study implementation of deterministic data paths for real-time applications with extremely low data loss rates, packet delay variation (jitter), and bounded latency, such as audio and video streaming, industrial automation, and vehicle control.

Audio Video Bridging (AVB) is a common name for the set of technical standards which provide improved synchronization, low-latency, and reliability for switched Ethernet networks. AVB embodies the following technologies and standards:

References

↑ "White Rabbit Overview" . Retrieved 2013-07-18.
↑ "The White Rabbit Project" (PDF). 2009. Retrieved 2013-07-18.
1 2 Moreira, Pedro; Serrano, Javier; Wlostowski, Tomasz; Loschmidt, Patrick; Gaderer, Georg (October 2009). "White rabbit: Sub-nanosecond timing distribution over Ethernet". 2009 International Symposium on Precision Clock Synchronization for Measurement, Control and Communication. pp. 1–5. doi:10.1109/ISPCS.2009.5340196. ISBN 978-1-4244-4391-8. S2CID 1724581.
↑ Moreira, Pedro; Serrano, Javier; Wlostowski, Tomasz; Loschmidt, Patrick; Gaderer, Georg (2009). "White rabbit: Sub-nanosecond timing distribution over ethernet". 2009 International Symposium on Precision Clock Synchronization for Measurement, Control and Communication. pp. 1–5. doi:10.1109/ispcs.2009.5340196. ISBN 978-1-4244-4391-8. S2CID 1724581.
↑ wikt:syntonization
↑ Monolithic phase-locked loops and clock recovery circuits : theory and design. Razavi, Behzad. New York: IEEE Press. 1996. ISBN 9780470545331. OCLC 557450248.{{cite book}}: CS1 maint: others (link)
↑ "KM3NeT - On-line detector control and Data Acquisition" . Retrieved 2016-01-20.
↑ "Technical Specification for Pulse and Steering Control Unit" (PDF). 2018. Retrieved 2018-11-25.
↑ "Open Hardware Repository Companies" . Retrieved 2013-07-18.
↑ "DEMETRA - Demonstrator of EGNSS Services based on Time Reference Architecture" . Retrieved 2019-02-19.
↑ Dierikx, Erik F.; Wallin, Anders E.; Fordell, Thomas; Myyry, Jani; Koponen, Petri; Merimaa, Mikko; Pinkert, Tjeerd J.; Koelemeij, Jeroen C. J.; Peek, Henk Z. (2016). "White Rabbit Precision Time Protocol on Long-Distance Fiber Links". IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 63 (7): 945–952. doi:10.1109/TUFFC.2016.2518122. ISSN 0885-3010. PMID 26780791. S2CID 11411374.

External links

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.

[White_Rabbit@OHWR-1] "White Rabbit Overview" . Retrieved 2013-07-18.

[The_White_Rabbit_Project-2] "The White Rabbit Project" (PDF). 2009. Retrieved 2013-07-18.

[Sub-nanosecond_timing_distribution_over_Ethernet-3] 1 2 Moreira, Pedro; Serrano, Javier; Wlostowski, Tomasz; Loschmidt, Patrick; Gaderer, Georg (October 2009). "White rabbit: Sub-nanosecond timing distribution over Ethernet". 2009 International Symposium on Precision Clock Synchronization for Measurement, Control and Communication. pp. 1–5. doi:10.1109/ISPCS.2009.5340196. ISBN 978-1-4244-4391-8. S2CID 1724581.

[4] Moreira, Pedro; Serrano, Javier; Wlostowski, Tomasz; Loschmidt, Patrick; Gaderer, Georg (2009). "White rabbit: Sub-nanosecond timing distribution over ethernet". 2009 International Symposium on Precision Clock Synchronization for Measurement, Control and Communication. pp. 1–5. doi:10.1109/ispcs.2009.5340196. ISBN 978-1-4244-4391-8. S2CID 1724581.

[Syntonization-5] wikt:syntonization

[6] Monolithic phase-locked loops and clock recovery circuits : theory and design. Razavi, Behzad. New York: IEEE Press. 1996. ISBN 9780470545331. OCLC 557450248.{{cite book}}: CS1 maint: others (link)

[detector_control@KM3NeT-7] "KM3NeT - On-line detector control and Data Acquisition" . Retrieved 2016-01-20.

[Technical_Specification_for_Pulse_and_Steering_Control_Unit-8] "Technical Specification for Pulse and Steering Control Unit" (PDF). 2018. Retrieved 2018-11-25.

[WR_Companies-9] "Open Hardware Repository Companies" . Retrieved 2013-07-18.

[DEMETRA-10] "DEMETRA - Demonstrator of EGNSS Services based on Time Reference Architecture" . Retrieved 2019-02-19.

[11] Dierikx, Erik F.; Wallin, Anders E.; Fordell, Thomas; Myyry, Jani; Koponen, Petri; Merimaa, Mikko; Pinkert, Tjeerd J.; Koelemeij, Jeroen C. J.; Peek, Henk Z. (2016). "White Rabbit Precision Time Protocol on Long-Distance Fiber Links". IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 63 (7): 945–952. doi:10.1109/TUFFC.2016.2518122. ISSN 0885-3010. PMID 26780791. S2CID 11411374.

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]