 and what is dynamic. Generally, carrying PTP over many nodes (using IP) that do not process PTP can introduce an excess of dynamic asymmetry. Dynamic asymmetry, by its very nature, cannot be corrected for, although it can be filtered to reduce its impact. So, the calculation used to determine the offset from master and the one-way delay can include cal- culations that include this extra correction factor. Returning to Figure 7-3, if the transit time from master to slave was known to be 4 ms instead of 2 ms, then an extension to the equations could eas- ily accommodate that knowledge and compensate for the error and allow accurate time to be re- covered. The IEEE 1588-2008 standard does this with the use of the delayAsymmetry attribute. The attribute delayAsymmetry is defined as follows (you can see that the value is defined to be pos- itive when the master-to-slave propagation time is longer than the slave-to-master propagation time): tms=<meanPathDelay> delayAsymmetry <meanPathDelay> - delayAsymmetry This delayAsymmetry is added to the correctionField (covered in the next section) before the calcu- lations of meanPathDelay and offsetFromMaster are done. It is the authors' opinion that outlining these expanded equations to include compensation is not re- quired to understand how PTP time recovery works or how to deploy it. To include these extra cal- culations just makes the mathematics more complex and is an impediment to learning. If you are interested in an example of asymmetry compensation, see the following section "Asymmetry Cor- rection" and the section "Correction and Calibration" in Chapter 9. For now, it is enough to recognize that asymmetry compensation can be done if the operator under- stands the likely error and that PTP implementations include the ability to configure and com- pensate for this error See clauses 11.6 and 7.4.2 of the IEEE 1588-2008 standard for more details. 7.3.1 The Correction Field The earlier section on the mathematics of PTP mentioned the use of the correctionField as a mech- 