Granted Patent
Utility
US 6,301,355 · App. 09/128,485
Method and apparatus for analyzing dual tone multi-frequency (DTMF) signals on a private branch exchange (PBX) switch
Inventor:
Cliff Sui
Patented Case
View Patent ↗
Granted: Oct 9, 2001
Filed: Aug 4, 1998
Inventor
Cliff Sui
Assignee (at issue)
Avaya Technology LLC
This patent predates the USPTO's electronic file wrapper — prosecution documents from this era exist only in the Patent Office's paper records. A certified copy of the file history can be ordered from the USPTO's paper archives.