Routing system for linear add-drop multiplexer

A routing system for a linear add-drop multiplexer having a first drop switch connected to a first transmission line, a second drop switch connected to a second transmission line, a channel switch for lower levels connected to the first drop switch and the second drop switch and a controller for providing a selection signal, comprising:

• a first selection switch, provided in said first drop switch, for selecting one of a first plurality of channels connected to the first transmission line and outputting a first output signal transmitted through the selected channel;
• a first selector, provided in said first drop switch and coupled to said first selection switch and the controller, for selectively outputting and inhibiting the first output signal transmitted from said first selection switch to produce a first signal based on the selection signal;
• a second selection switch, provided in said second drop switch, for selecting one of a second plurality of channels connected to the second transmission line and outputting a second output signal transmitted through the selected channel;
• a second selector, provided in said second drop switch and coupled to said second selection switch and the controller, for inhibiting the second output signal transmitted form said second selection switch when said first selector outputs the first output signal, and for outputting the second output signal when said first selector inhibits the first output signal to produce a second signal based on the selection signal;
• and
• output means, provided in said channel switch, for selectively outputting the first and second signals transmitted from said first and second selectors to a transmitter/receiver for lower signal levels;
• said first selection switch including means for providing, as the first output signal, a third signal transmitted through said selected channel and a fourth signal having all data bits set to 0;
• said first selector comprising means for selecting and outputting one of said third and fourth signals as the first signal;
• said second selection switch including means for providing, as the second output signal, a fifth signal transmitted through said selected channel and a sixth signal having all data bits set to 0;
• said second selector comprising means for outputting, as the second signal, the sixth signal when said first selector outputs the third signal and the fifth signal when said first selector outputs the fourth signal.