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Synchronous Ethernet clocks, based on ITU-T G.813 clocks, are defined in terms of accuracy, noise transfer, holdover performance, noise tolerance and noise generation. These clocks are referred as Ethernet Equipment Slave clocks. While the IEEE 802.3 standard specifies Ethernet clocks to be within ±100 ppm. EECs accuracy must be within ±4.6 ppm.
The Time-Triggered Ethernet (SAE AS6802) (also known as TTEthernet or TTE) standard defines a fault-tolerant synchronization strategy for building and maintaining synchronized time in Ethernet networks, and outlines mechanisms required for synchronous time-triggered packet switching for critical integrated applications and integrated modular avionics (IMA) architectures.
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.
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.
Ideally, clocks in a telecommunications network are synchronous, controlled to run at identical rates, or at the same mean rate with a fixed relative phase displacement, within a specified limited range. However, they may be mesochronous in practice. In common usage, mesochronous networks are often described as synchronous.
The Precision Time Protocol (PTP) is a protocol for clock synchronization throughout a computer network with relatively high precision and therefore potentially high accuracy. . In a local area network (LAN), accuracy can be sub-microsecond – making it suitable for measurement and control systems.
In contrast to standard Ethernet according to IEEE 802.3 and Ethernet bridging according to IEEE 802.1Q, time is very important in TSN networks.For real-time communication with hard, non-negotiable time boundaries for end-to-end transmission latencies, all devices in this network need to have a common time reference and therefore, need to synchronize their clocks among each other.
The master clock in a clock network can receive accurate time in a number of ways: through the United States GPS satellite constellation, a Network Time Protocol server, the CDMA cellular phone network, a modem connection to a time source, or by listening to radio transmissions from WWV or WWVH, or a special signal from an upstream broadcast network.