PDF of this tutorialProviding twisted copper pair, the LEC acts as a wholesaler of copper or spectrum to other carriers or network providers, managing the outside plant on either a pure connectivity or spectrum basis. In furnishing the copper plant, the LEC has closest physical proximity to DSL subscribers but maintains the most remote business/service relationships with them.
The LEC’s infrastructure enables broadband DSL services over copper (see Figure 3). From within the LEC’s facilities, copper loops enter the central office, pass through a main distribution frame (MDF), and link to a voice switch attached to a POTS test system. From a DSL modem, data flows through the customer-premises equipment (CPE), MDF, a test access system, and then into co-location facilities of the DSL provider—the NAP.
Figure 3. The LEC’s Infrastructure Provides the Copper Loop in the DSL Supplier Value Chain
In earlier DSL rollouts, many LECs provided little-to-no service assurance for unbundled copper loops. To address service problems within the loops, a LEC would dispatch a technician with handheld gear to drive to the central office, examine the loop, diagnose the problem, and then dispatch yet another technician for repair. Even worse, many LECs still cannot communicate the status of repairs within their operations or to customers, informing them of a problem’s assessment, repair, test, and resolution.
Only recently have LECs begun to provide service assurance of broadband DSL services through interconnection agreements, which specify their obligations for bandwidth, capacity, and availability. Slow and resource-consuming, the redundant double-dispatch method cannot support today’s and tomorrow’s needs of enterprise customers. With increasing dependence on the Internet for data applications, businesses and governments can’t tolerate e-mail failures, dropped connections to extranets or public Web sites, or lengthy time to repair. To protect business resources, they now negotiate the time and specifics of repair before issuing a release to the LEC to diagnose and fix network problems. In light of these stringent requirements, LECs must keep the testing processes as rapid and nonintrusive as possible.
Current POTS test systems will not support DSL’s wideband testing requirements and cannot measure accurately the broadband spectrum of DSL (see Figure 4). Designed for metallic continuity and narrowband voice measurements, POTS test systems measure only a narrow spectrum of information made available through the no-test trunk of switches, e.g., the voice band. With little overlap between spectrums, copper-dedicated systems lack the span to measure DSL bandwidth accurately.
Figure 4. POTS Test SystemsAll these challenges underscore the need to automate and centralize the management of the LEC’s service assurance processes. Through the ability to detect, isolate, and resolve network faults automatically—from or close to the co-location point—LECs can avoid costly and slow manual dispatches and pass cost savings onto their NAP customers.
