D4 Digital Channel Bank Family: Dataport - Channel Units for Digital Data System 56-kb/s Rate

Consider the use of existing T-carrier facilities to extend the Digital Data System (DDS) serving area. "Dataport" channel units are needed for the carrier terminals (such as D4 channel banks) to insert customer data bit streams into the carrier pulse code modulation (PCM) bits tream. Special problems must be addressed with 56-kb/s service; hence, dataports for this speed are treated separately from those for subrate speeds. Field studies of the performance achieved by T-carrier facilities1 indicate that a significant number of them , if used to carry DDS channels, will fail to meet an overall quality objective of 99.5-percent error-free seconds. T-carrier lines are designed and engineered for a 2741 OFFICE CHANNEL UNIT DATAPORT DSO DATAPORT s Fig. 1--Basic dataport application.