Two-way delay measurement is similar to one-way delay measurement except it measures the round trip delay from the generating MEP. In this case, clock synchronization issues do not influence the round-trip test results because four timestamps are used. This allows the time it takes for the remote node to process the frame to be removed from the calculation, and as a result, clock variances are not included in the results. The same consideration for first test and hardware based time stamping stated for one-way delay measurement are applicable to two-way delay measurement.
Delay can be measured using one-way and two-way on demand functions. The two-way test results are available single-ended, test initiated, calculation and results viewed on the same node. There is no specific configuration under the MEP on the SAP to enable this function. An example of an on demand test and results are below. The latest test result is stored for viewing. Further tests overwrite the previous results. Delay variation is only valid if more than one test has been executed.