Closing the Loop

The copper-loop environment is discussed in detail in Section A.3.1.1. Guidelines, developed in the 1980s for Carrier Serving Areas (CSA), produced excellent results for analog services. Additional study was needed, however, to ascertain the extent to which Basic Rate Access (BRA) ISDN could be deployed over copper loops. It was found that about 25% of all copper loops could not carry the required 160 kb/s because of loading coils installed in the loops. It also was found that about 48% of the sampled loops were compatible with CSA guidelines. Other loops in a CSA extend far beyond the maximum guideline length and are provided with Digital Loop Carrier (DLC) in the feeder portion. A Feeder Distribution Interface (FDI) is connected on the subscriber side of the DLC Remote Terminal (RT) and is designed to serve 400 to 600 subscribers.

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