This issues a one-time command to this port's BERT engine: start, stop, clear its accumulated counters, or inject a single error. As the actual control switch for the test, this object on this specific port is what starts and stops the BERT session configured by the other pportBert* pattern and rate settings, distinct from them just defining what the test would do if run. After configuring pportBertPattern and pportBertErrorRate for this port, an admin would write start to pportBertCommand to actually begin the test, then stop when finished.