News from 2005-06-14


Precision Time Protocol (IEEE 1588) Time Server



Higher Accuracy over the Network - with PTP

Network Time - Innovation through Cooperation

Being the first manufacturer of NTP Time Server equipment, Meinberg developed a LANTIME version with PTP support , which will enable the successful LANTIME family to synchronize PTP compatible clients over the network. PTP reaches a very high level of accuracy by his concept of hardware time stamps.


While most end users can live fine with the accuracy offered by other time sync protocols like the well-known Network Time Protocol (NTP) (with NTP a sub-milisecond accuracy is possible, but depends on network architecture and -traffic), especially in the field of process automation and measurement data logging there is often a requirement for higher accuracy.

To satisfy people in need of a very high network-sync accuracy the IEEE 1588 Standard for A Precision Clock Synchronization Protocol for Networked Measurement and Control Systems has been created, the defined protocol is known as "Precision Time Protocol" (PTP) and reaches sub-microsecond accuracy.


LANTIME/PTP

As a first functional prototype a LANTIME with integrated GPS receiver has been modified by adding an additional ethernet network interface with integrated time-stamping-unit (TSU). This TSU is time-stamping incoming and outgoing PTP packets with a high accuracy. The system ("PTP master") can be used as a Grandmaster clock in a PTP network and not only provides a very good relative synchronization between the PTP clients, they also get the UTC based absolute time.

A second unit without GPS receiver ("PTP slave") has been used in a test environment trying to synchronize it with over the network with the PTP master unit. During the tests the PPS signals of both units have been compared constantly and the measurement of the offset between them allows to draw conclusions regarding the accuracy which is can be reached over a network connection.

The image shows the result of a one-hour test run, an offset of nearly 60ns could be measured at this point. After 12 hours the accuracy settled around 100ns.

Actual State of Development

The first prototypes are running fine and are further optimized at the moment. The goal is to offer a PTP option for the LANTIME family to the Meinberg customers. Meinberg is planning to participate in the IEEE 1588 Conference in October 2005 in Winterthur, Switzerland. The plug-fest event which is organized during the conference will be a good chance to test interopability of the prototypes with other PTP products.

If you need further details regarding PTP or Meinberg products, please do not hesitate to contact us: info@meinberg.de.


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