The DSU transmit buffer option. An optional elastic transmit buffer is inserted into the data path when a value of external(2) is selected. This elastic buffer maintains network synchronization when an external frequency locked clock source is driven into the external transmit clock input on the DTE interface. Opposing phase relationships between the external transmit clock and network clock are compensated for by this buffer. No buffering is performed when this object is internal(1). If the transmitter timing is set to external, this object must be set to external(2).