This read-only Counter reports the count of transmit underruns detected on the CPE's DSL interface during the hour, tracked hourly on the CPE side of the DSL link. Operationally, underruns on the CPE side point to the customer's own equipment failing to keep the transmit pipeline fed, distinct from a line-card-side problem at the head end. For example, if the CPE's hourly underrun count rises while the head-end's cmDSLIntervalTxUnderruns for the same hour stays flat, the fault likely lies in the customer's own equipment.