A read-only value that reports the MPCP round trip time
in increments of Time Quanta (TQ) 16ns. The value
returned shall be (round trip time in ns)/16. If this
value exceeds (2^16-1) the value (2^16-1) shall be
returned. This attribute is relevant for an OLT and an
ONU. For the OLT there is a value per LLID