BROOMFIELD, Colo., July 20 -- Level 3 Communications Inc. will get more than $100 million to provide CoreExpress, an extranet infrastructure company in St. Louis, with 23,000 miles of dark fiber over a 20-year period. Dark fiber is fiber that has been installed without the required electronics to transmit information, Carriers, ISPs and other Web-centric companies purchase dark fiber from us because it affords them the advantages of network ownership without investing in the capital outlay to construct one, said Pawan Jaggi, vice president of global transport services for Level 3. CoreExpress will light the fiber to assemble its Internet Data Exchange System, the first multi-ISP extranet platform, said CoreExpress. Dark fiber allows CoreExpress to regularly assemble its optical technologies and upgrade those systems throughout the contract period in order to increase the useable bandwidth of its fiber, the company said. The agreement also provides CoreExpress the opportunity to buy a full inter-city network conduit from Level 3 in the future.