Paragon-X/Paragon-neo: In BC Test Mode, why do I see very high T1 and T4 time error when connected back-to-back?

Owned by Kevin Godfrey
Last updated: Apr 23, 2021
1 min read

This is what you should expect when in BC test mode and connected back-to-back.

What you are measuring are the internal port 1 ingress and egress delays. The Paragon PTP timestamper is inside the instrument (not aligned to the edge of the instrument). The delays are symmetric so as not to cause 2Way time error.

When testing a BC, the PTP reference time comes from the Paragon master on port 1. The slave of BC being tested will see the port 1 internal delays as if there was a long cable / fibre to the master - it will calculate the delay to the Paragon master timestamper and recover time based on that delay calculation. In other words, the BC slave will take account of the Paragon port 1 internal delay when recovering time.

The ingress and egress delays on Paragon port 2 (the Paragon slave) are included in the time error calculation i.e. these delays are known and the Paragon takes account of them to produce an accurate time error measurement.

So, in summary, when connected back-to-back, the Paragon slave on port 2 is measuring the ingress and egress delays on port 1. These delays have no effect on time error measurements when testing with a real BC.