cmV35TxClockSource is a read-only enumeration reporting whether the transmit clock for a V.35 port is being sourced internally or from the external connected equipment. An administrator checks this to confirm the port's clocking configuration matches expectations, since a mismatched clock source between two ends of a leased line can prevent synchronization. For example, if a V.35 port intended to use external clocking instead shows cmV35TxClockSource as clock-int, the operator would investigate why it fell back to its internal clock source.