Definity TN420C Tone Detector  Detects and analyzes tones on the Time Division Multiplexing (TDM) bus.  Provides two Network Processing Elements (NPEs) with eight channels that provide four Dual Tone Multi-Frequency (DTMF) receiver ports, two general purpose tone detector ports, and two digital loop-around ports.  TN420C replaced by TN2182B and TN744D.