Source of the transmit and receive clocks.

    external    The modem provides the clock.

    internal    The communications device provides the clock.

    reflected   The DTE transmit clock is a reflection of the
                DCE transmit clock. This minimizes the clock to
                data skew that the DCE encounters when high line
                speeds are used.

    The default value depends on the setting of the characteristic
    communications mode. If communications mode is asynchronous, the
    default value of this characteristic is internal. Otherwise, the
    default value is external.

    The value of this attribute has no effect when the communications
    line is in loopback mode. In this case, the type of loopback
    determines the type of clock. You can modify this characteristic
    only when the entity is disabled.