Communication unit, control apparatus, field device, communication system and method

A method for providing an output data stream, comprising the steps of:

• receiving, with a communication unit, an input data stream;
• determining clock information based on an input symbol clock of the input data stream and an internal reference clock signal of the communication unit;
• and
• providing, using the clock information, the output data stream with an output symbol clock whose clock rate is equal to the clock rate of the input symbol clock,
• wherein the internal reference clock signal is coupled with an internal clock signal of the communication unit, and wherein an internal clock generator of the communication unit generates the internal clock signal independently of the input symbol clock and/or the output symbol clock.

A communication system comprising a first communication unit and a plurality of second communication units, the second communication units each comprising a first input and a first output and each being configured to receive, via the first input, an input serial data stream having payload data and to output, via the first output, an output serial data stream having payload data, wherein each second communication unit is configured to determine, on the basis of an internal reference clock signal of the respective second communication unit and an input symbol clock of the input data stream, clock information and to provide, using the clock information, the output data stream with an output symbol clock whose clock rate is equal to the clock rate of the input symbol clock, wherein the first communication unit has an output and an input and the second communication units each further have a second input and a second output, wherein the communication units are connected in series, such that a communication path is provided which, starting from the output of the first communication unit, runs in the order prescribed by the series successively through each first input and each second output of the second communication units to the first output of the last second communication unit in the series, and from there runs in reverse order successively through each second input and each second output to the input of the first communication unit, wherein each first and second communication unit has its own internal clock generator and the internal clock generators of the first and second communication units are not synchronized with each other.