An entry in this table contains an available clock source
on the device.
A source of network clock for the device may be an oscillator
local to the device or a Building Integrated Timing Supply (BITS)
port or an interface that supports synchronous clock recovery.
An index is assigned by the device to uniquely identify each of
the source of networking clock on the managed system.
A description is associated with each clock source.
This description gives detail information of this clock source.
The management station should poll this table to obtain
these 'cwnClockSourceIndex' and use these indexes
to configure clock source in
'cwnManualSourceTable' or 'cwnAtmSourceTable'.