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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 Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks. In operation since before 1985, NTP is one of the oldest Internet protocols in current use.
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. [ 1 ]
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.
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.
The aim of Synchronous Ethernet is to provide a synchronization signal to those network resources that may eventually require such a type of signal. The Synchronous Ethernet signal transmitted over the Ethernet physical layer should be traceable to an external clock, ideally a master and unique clock for the whole network.
The time reference used by a time server could be another time server on the network or the Internet, a connected radio clock or an atomic clock. The most common true time source is a GPS or GPS master clock. Time servers are sometimes multi-purpose network servers, dedicated network servers, or dedicated devices. All a dedicated time server ...
TDMA frame structure showing a data stream divided into frames and those frames divided into time slots. Time-division multiple access (TDMA) is a channel access method for shared-medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. [1]