A central office line unit (COLU) for a pulse code modulation (PCM) upstream and downstream system in a universal digital loop carrier (UDLC) includes a hybrid circuit for transmitting/receiving an analog signal to/from a switch. An analog-to-digital converter is provided for receiving the analog signal...http://www.google.ca/patents/US6785340?utm_source=gb-gplus-sharePatent US6785340 - PCM upstream and downstream system for universal digital loop carrier
