Lesson 2: Redundancy Matters

Muscle power was aided immeasurably by one feature Verizon built into its network before Sept. 11.

Verizon had installed redundant connections between its central offices so a cable failure on one route wouldn't disrupt communications. Although the redundancy did not allow Verizon to immediately restore service, technicians ran aboveground cables to an undamaged portion of a redundant line that connected 140 West to a central office on Canal Street, several blocks north of Ground Zero.

Without the redundancy, Verizon would have taken weeks to dig up streets and connect 140 West to the Canal Street facility—assuming equipment was available to dig the trenches.

After Sept. 11, Verizon put 18 optical communications rings into place in Lower Manhattan. With these rings, which use Synchronous Optical Network (SONET) technology, a failure between two points can be overcome simply by reversing the direction of traffic.

Even with the SONET rings, Verizon's data network in Lower Manhattan is not fail-safe. A knockout of 140 West will still cause the network to fail. But now Verizon's network will operate if damage or disaster disables part of a ring.