A method and apparatus for handling, maintaining, and controlling network
synchronization information emanating from a plurality of line card
circuits is described. The technique described may be applied to a
redundant pair of line card circuits, where one line card circuit is
active, while the other is inactive. Line card activity latches are
managed by means of hardware logic that may be configured at the time of
line card commissioning. The activity latches are coupled to a logic
element. An incoming clock signal is applied to the logic element. If an
activity latch indicates that a line card circuit is active, the logic
element provides the incoming clock signal as an outgoing clock signal to
a control card circuit. If the activity latch indicates that the line
card circuit is inactive, the logic element blocks the incoming clock
signal from being passed and provides a static output level as the
outgoing clock signal to the control card circuit. The control card
circuit is provided with circuitry to receive the outgoing clock signals
from multiple line card circuits. The circuitry is sensitive to whether
or not the line card circuits are configured for redundant operation. One
or more of these clock signals are then selected and used for network
synchronization.