VIAVI TestCenter : How does VIAVI makes and puts the time stamps when it is acting as a DM responder.

VIAVI TestCenter : How does VIAVI makes and puts the time stamps when it is acting as a DM responder.

In most cases the DUT is supposed to be one injecting TxTimestampb and RxTimestampf and VIAVI TestCenter does the Round Trip time (RTT) calculation. If VIAVI is injecting these timestamps they should not have much significance. These are only indicative of VIAVI’s internal packet processing time which can be ignored. We should only pay attention to the total RTT calculation. Below is a typical EOAM Delay measurement usecase:       If VIAVI TestCenter is sending the Delay Measurement Message(DMM) and DUT responds with Delay Measurement Responder (DMR)   • DUT injects TxTimestampb and RxTimestampf in DMR. • DUT internal processing time = TxTimestampb – RxTimestampf. • VIAVI TestCenter RTT = RxTimeStampb - recorded Tx hardware timestamp If DUT is sending DMM and STC is sending DMR, injecting TxTimestampb and RxTimestampf. • Total RTT on DUT= RxTimestampb –TxTimestampf When VIAVI TestCenter receives DMM and sends DMR, the RxTimeStampf is a hardware timestamp and TxTimeStampb is a CPU timestamp. When VIAVI TestCenter receives DMR, the RxTimeStampb is hardware timestamp, TxTimeStampf is a CPU based timestamp but it is not used for RTT measurement For round trip time calculation on VIAVI TestCenter, it doesn't simply equal to RxTimeStampb - TxTimeStampf. Although we are not able to insert the hardware timestamp in DMM packet,  VIAVI TestCenter will keep a record of the actual Tx hardware timestamp when DMM is transmitted, which is the best we can do. Then when corresponding DMR is received, the round trip time RTT = RxTimeStampb - Recorded Tx hardware timestamp. This is very accurate and no CPU timestamp is involved in the RT time calculation.