This document contains a list of Frequently Asked Questions (FAQ). Entries are not listed in any particular order or priority.
IEEE1588 enables high-accuracy synchronization of clocks over the Ethernet. With it’s close to wire implementation, OnTime can achieve better than 50 ns synchronization between a Grand Master clock and a slave clock.
PTPv2 introduces many features to IEEE1588 that add flexibility and accuracy to the standard. PTPv2 offers higher effective resolution when communicating time stamps and additional flexibility in communication, by introducing unicast messaging and more flexible sync message rates. Version 2 also adds transparent clock functionality, which enables two devices to synchronize accurately when separated by intermediate network devices.
The second version is not back compatible with the first version of the standard. A PTP V1 device cannot be synchronized with a PTP V2 device due to the diffirence generated by the new message format of the PTP V2. In order to permit the retro compatibility, OnTime has implemented a specific feature that allows PTP version configuration per port. And thus make possible network with both PTP implementation.
The concept of PTP is to be able to achieve sub microsecond accuracy through an Ethernet network. Using equipment that has no support for hardware timestampling will deteriorate this precision and the main aspect of the protocol and its purpose will be lost. In order to support the best capability of the PTP the whole network from the masterclock down to the slave clock must have a 1588 implementation, preferably with a close to wire implementation.
The accuracy is directly link to the implementation of the protocol. The closest to the wire the time stamping is done, the better is the accuracy.
The number of steps associated with a clock denotes the steps required for the clock to exchange its time-stamp data. One-step clocks are capable of inserting the time-stamp data of outgoing packets into the packet itself, whereas two-step clocks send the time-stamps of packets separately. This is easily seen in sync packet transmission – one-step clocks insert the egress time stamp of sync packets into the sync packet itself, whereas two-step clocks send the egress time stamp of a sync packet in a separate “follow-up” packet.
The Transparent clock is the mechanism that compensates for the residual latency and corrects the time stamp in the synchronization message whereas the Slave clock is the regulation algorithm that compensate for the clock drift of the network element. Both must coexist to reach the best accuracy.
A grand Master Clock, commonly named GMC, is the network element that is linked to a GPS receiver and gives the time in forms of UDP messages according to the 1588 standard.
The Best Master Clock Algorithm is a software mechanism that determines which Grand Master clock with the same subnet has the best resolution. The comparison is done according to several criteria such as the priority, the clock class, the clock accuracy…
The transparent clock is generaly implemented in the switch. Its purpose is to compensate for the residual latency generated by the switch itself. The Transparent clock will modify the time stamp generated by the Grand Master with its actual time. In the point of view of a slave clock it will appear that it is directly connected to the Grand Master. Together with the Best Master clock algorithm, this implementation avoids that 2 Grand master act as Master in the same network.
The OnTime Networks’ devices are specifically designed to operate in the harsh and climatically demanding environments of the aerospace and defense industry, today the systems are widely used in FTI network. Our rugged systems are at the forefront of technology and provide innovative solutions that address complexity, enable modularity while delivering optimal performance for SWaP-C (Space/Weight/Power/Cost) constrained applications.