This read-write attribute selects the timing source for the ComController's synchronization clock, either internalClk or networkClk, and when networkClk is chosen one of the OC3 cards must be designated as the primary timing source with an optional secondary, falling back to internalClk automatically if no OC3 card is present. This decides whether the headend's timing is derived from an external network reference via OC3 or simply free-runs on its own internal oscillator, which matters for any synchronous transport requirements on that plant. For example, a headend equipped with OC3 cards for a synchronous transport network would set hcxSyncClkConfigure to networkClk and designate a primary OC3 card as the timing reference rather than relying on the free-running internal clock.