A digital bypass unit for a PBX or ACD telephone system having T1 spans provides the capability to place and answer calls on a digital T1 span in the event of a system failure or power failure. The bypass unit permits the bypass of the failed system, connecting T1 channels directly to digital telephone...http://www.google.fr/patents/US5214692?utm_source=gb-gplus-shareBrevet US5214692 - Bypass for telephone switching system
