Evolution of a systems plan for advanced communications within a rapid transit system

The Chicago Transit Authority (CTA) is embarking on a number of programs to introduce advanced technologies throughout their 100+ year old system. A combination of rehabilitation projects, new construction projects, operational improvements, and public/private partnerships will be the key to achieving the goal of advanced system-wide communications and ultimately may form the basis for a system-wide Intelligent Transportation Systems (ITS). A system-wide fiber optic communications backbone was designed to facilitate all voice, data, and video communications within the CTA. The backbone design was based upon a SONET self-healing ring configuration, with redundant hardware and cabling to prevent a single contingency failure anywhere in the system. Although each transit line would be set up as a unique ring, a common area geographical loop was identified for the primary network ring. This common backbone loop (CBL), routed along various subway, at-grade, and elevated lines, was designed for a dual cable, self-healing SONET OC-12 architecture. The dual OC-12 rings interfaced major nodes with two independent switching points to facilitate disaster recovery. The CBL was designed to allow for ease of expansion as additional lines were implemented. Each line used an OC-3 dual ring self-healing architecture. These rings were routed to two separate OC-12 nodes for network integration on the CBL instead of routing a series of nonnetworked rings back to the control center. This paper describes the original backbone design and the evolution of that design as current and future projects are implemented within the CTA