A subscriber link to a central office which employs data compression, forward error correction, and advanced modulation techniques and to connect subscribers to multiple communications networks to provide an array of services. A device provides normal telephone service in the event of an equipment failure....http://www.google.com/patents/US7394757?utm_source=gb-gplus-sharePatent US7394757 - Circuit to provide backup telephone service for a multiple service access system using a twisted pair
