An interface to an integrated service, digital network (ISDN) line for up to two analog dual tone, multifrequency telephones and up to four personal computers or data terminals. A stored program-controlled processor controls access to the ISDN line for the analog and digital interface circuits. The processor...http://www.google.de/patents/US5305312?utm_source=gb-gplus-sharePatent US5305312 - Apparatus for interfacing analog telephones and digital data terminals to an ISDN line
