Timing, network synchronization, clocking...whatever you want to call it, simply means that your DTE and the carrier have to agree on a common clock in order to pace out the bits that make up the voice calls. Telcos ALWAYS have more reliable clocks than your own gear, so this value is almost always set to "Network".
Look for related programming parms in your DTE and set it for "Network"; this will force the box to derive it's timing from the carrier.
I'm hoping that James will chime in here as I do not know what the Asterisk folks have chosen to rename this parameter. "Zap Omega", perhaps? They call T1 trunks "Zap" trunks, so why not? Those Asterisk people want to change everything
