This is the read-only counterpart to nndsxT3E3IfConfigTransmitClock, reporting whether the interface is actually transmitting using the recovered receive clock from another T3/E3 port (timing-line) or its own local oscillator (timing-internal). Administrators check it to confirm the timing configuration actually took effect, since a misconfigured clocking chain across several back-to-back T3/E3 ports is a classic cause of intermittent slips and errored seconds.